Bosch D-Jetronic Fuel Injection Notes Compilation
10/2015 R. Kwas  changes/additions ongoing
Most recent changes:  Mar 2024  [Notes/Comments added.]  

Update:  I have recently rearranged this page, with the goal of improving the organization of this complex system, which has so much interaction between electronic and fuel-contact components. It is now organized by control circuit ECU Sheets (based on the Kerfoot drawings), including those sensors which interface associated with those sheets, allowing a better holistic electronic understanding by those able to follow the electronic interaction.  It is my position that this can help with the general understanding of function, and troubleshooting which may need to occur. 

Caution:  When working with the pressurized D-Jet (or any other) FI System, use EXTREME CARE to be ready for, protect yourself from, and catch possible/likely squirting or fuel in the open, and observe fire prevention practices!  ...and having a fire blanket and extinguisher at hand when working with fuel in the open can't hurt! 


General Information and Acknowledgements

Bosch D-Jetronic Circuit.  Sheet 1
    Distributor Contacts
    Dynamic and Static Injector Test Notes

    Manifold Pressure Sensor

Bosch D-Jetronic Circuit.  Sheet 2
    Throttle Position Sensor (TPS)
    TPS Update
    TPS Conjecture
    Setting the Idle on a D-Jet
    Fuel Pump Control
    Cylinder/Coolant Temperature Sensor 

Bosch D-Jetronic Circuit.  Sheet 3

D-Jet Wiring Interconnection Diagrams
    71 1800E Fuel Injection Wiring Diagram
    73 1800ES Fuel Injection Wiring Diagram 
    Thermo-Time Switch

    Cold Start Injector

D-Jet Fuel Handling Components
Measuring Fuel Rail Pressure

    Relieving Fuel Rail Pressure
    Fuel Pump
    Fuel Pump Function
        Rattling noise at Fuel Pump
    Fuel Pressure Regulator
    Fuel Rail Pressure Drop due to Feed Restriction
    Fuel Injectors
    Injector Cleaning
    Fuel Line

D-Jetronic Service Tips and Techniques
    Vacuum Leaks

    Aux Air Valve
    Aux Air Valve Alternative

    Chassis Connections for D-Jet
Reference Information
    Service and Troubleshooting Documentation
    Marked up Wiring Diagram for D-Jet Troubleshooting
    Throttle Position Switch (TPS) Additional
    Volvo Fuel Injection Fault Tracing
    Reproduction Parts for D-Jetronic 
    Working Diagram tying all TPS info together
    The Edge Triggered Flip-Flop
    Distributor Contacts of the Bosch D-Jet

    Links and Troubleshooting Thread Excerpts

        non-running 1800ES

Fact-checking wikipedia!

Links to related SW-EM Pages: 
    D-Jet Idle Adjustment

    In Progress, and not yet on-line:  Bosch D-Jetronic TPS and Miss at Cruise (MaC) Investigation


General Information and Acknowledgements: 

The Bosch D-Jetronic is an analog Electronic Control Unit (ECU) developed in the sixties, when micro-processors were not jet available for general use, but this is not to say that the complex calculations crunched digitally by screaming fast Arithmetic Logic Units (ALU) of today's Injection ECUs, were not perfectly capable of being processed by analog transistors back in that period (recall that we DID get to the moon and back using analog control circuits...OK, they did have a computer along, but it had less smarts than your new espresso maker!).  See also:  Fact-checking wikipedia!

Unfortunately, the lack of a processor and memory also means that the D-Jet ECU does not continuously monitor that the sensors and actuators are operating within a "normal" operating range, and remembers when they go out of range, to help with subsequent troubleshooting.  Failure locating on the D-Jet requires an understanding and insight into the system's operation...and a bit of experience can't hurt either.  Point is that troubleshooting the D-Jet is not as simple as asking the computer "what hurts?" does take more smarts and interpretation of symptoms on the part of the troubleshooter.  Fortunately, after such a long time, there are few difficulties which have not been encountered and previously documented.  

The material compiled here is in addition to the comprehensive documentation and troubleshooting information in the green Volvo factory manual as well as the Volvo Fuel Injection Fault Tracing booklet.  I have also included bits of what I recognized as being particularly valuable in info, or practical technique.  

All Volvo and D-Jetronic owners everywhere, particularly those of us who are electronically qualified and know what we're looking at, at the circuit level, owe a huge debt of gratitude to Frank Kerfoot, for the (enormous) time and effort that he undoubtedly expended, reverse engineering the circuit of the Bosch ECU.  It is published by Porsche 914 specialist Paul B. Anders who presents it, along with theory of operation and scope waveforms on his most excellent page:  ...and in checking the ECU connector pin numbers, they are the same as was used the Volvo application, so for a very large part, the info is similar and absolutely applicable.  However, some variations in the system exist, including by model year. 

It's dedicated enthusiasts and privateers (like also Dr. D-Jet in Germany, ) who help us all with their efforts and who prevent the big companies from having a monopoly on the information of what is inside their boxes.  It's not that we're about to take the information and make competition for them, but sometimes we need to know details for service and troubleshooting purposes! 


Bosch D-Jetronic (Model 039.906.021A) Circuit.  Sheet 1 (Credit:  F. Kerfoot): 

Sheet 1.  Timing Logic (TL, consisting of Distributor Contact triggered Flip-Flop, Edge Detector and NoOR Gates), Pressure-Sensing Loop (PL), Over-Run Shutoff (OS), Injection Logic (IL), Switching Logic (SL), and Output Drivers (D1 & D2).  Note:  I have added Mark-ups and Corrections based on actual component values observed during inspection of multiple ECUs. 

Distributor Contacts:

My answer to a question about adjusting the the Distrib Trigger Contacts:

"...D-Jet Distributor Trigger Contacts are not like Ignition Points in that they need a specific gap, being acted upon by a shaftlobe at a specific time and rotational position, because they simply trigger a Flip-Flip, similar to the TPS, and timing of this is not as critical as with Ign...but they can stand a periodic inspection, cleaning and lube to minimize wear of the rubbing block. There is nothing to adjust!"

A glance at the circuit diagram above shows that the Distrib Contacts connect into a Flip-Flop circuit which establishes the base injection frequency as a function of engine RPM.  The duration of power applied to the Injector pairs is then further modified as a function of Manifold vacuum, and sensed temperatures. 

See also:  Distributor Contacts of the Bosch D-Jet



Dynamic and Static Injector Test Notes:  

Note that output to Injectors at pins 3, 4, and 5, 6 run through 6Ohm 5Watt Resistors.  These serve to limit the current applied to Injectors (See also:  Dropping Resistors) and effectively drop the voltage actually applied Injectors to 3V.  They are then tied together internally to the transistor switches, therefore, Injectors fire in pairs!  1, 3 together, and 2, 4 together.  By deduction (and a careful application of Ohms Law), I therefore calculate the actual DC resistance of the Injectors to be:  1.3Ohms.  [The calculation which arrived at the 1.3Ohms uses values which are "rounded off"...the actual static Resistance measured with with a DVM, is ~2Ohms.  See also:  Evaluation of Test Setup shown in Video  ...not to overcomplicate the issue, the point it, Resistance of Injectors is quite low, and without current limiting provided by the Dropping Resistors, would result in a very high current if they simply had 12V applied directly.  See further considerations below!] 

Note:  These values are good enough for most service and troubleshooting work.  For those doing more detailed work, or just interested, the Injectors are really solenoids with moving armatures and complex impedance characteristics.  Mr. Anders has modeled these in pSpice and presents this on his site:  


Excerpt of Kerfoot drawing excerpt showing ECU output stage voltages, including on Injectors 1, 3 when associated transistor TX switch is ON. Note that Injector operating voltage is 3V (NOT 12V!), and this is a transient condition which can only be captured with a DVM with catch-and-hold feature, or an oscilloscope.  Snubber Circuit Values added.   [Note:  Voltages shown here are also nominal values for the purpose of discussion...they do not take into account precise details like actual bus voltage when Charging System is pulling it up, impedance change as solenoid moves, transistor voltage drops, etc.  The excellent B. Anders page on D-Jet has waveform captures which show these details and subtleties.  Ref: ]

My posting to thread: 
“....Injectors are NOT designed or intended for a full fact, applying this voltage directly would overheat and kill an Injector in short order (and guys who have applied a full 12V, even if only for test purposes, have lunched Lord knows how many like that)...DON'T DO IT!...

Elsewhere in that thread:  "Applying full 12V to an injector is a mighty hard (and risky!) hit electrically, but it might just be what it takes to mechanically free up a stuck Pintle...but do this NOT many times, judiciously (very briefly ONLY!), and at your own risk!! A [much, much] better [and way less risky!] technique for freeing up a stuck Pintle would be a solvent soak (I suggest carb cleaner, Marvel Mystery Oil mix), then applying 12V through a Dropping Res and momentarily, just like in normal operation! risk of hurting the Injector then! ...but if this does not free Pintle, I'd say OK to applying double voltage momentarily (by reducing DR to 2.5Ohms, and monitor Injector temp during tests!)[or returning to the solvent soak for a week!] practice is to NEVER apply a full 12V or continuous's just too risky!" 

Some quick Ohms Law power calculations to drive home how very stressful and BAAAAAD, applying an uncurrent-limited 12V is: 
P = V2 / R

Calculated for (normal 3V operation):  (3x3) / 1.3 = 6.9W

Calculated for (very abnormal!! 12Voperation):  (12x12) / 1.3 = (a whopping 110.7W!) ...repeating:...DON'T DO IT!...

See also separate SW-EM page:  D-Jet Injector Maintenance and Service Notes

See additional info on Injectors below:  Fuel Injectors, Injector Cleaning 

See also (reference info about Voltage Collapse of a source due to internal Resistance):

Placeholder for Notes on Snubber Circuits: 


Manifold Pressure Sensor (MPS): 

This is a Variable Transformer sensing the pressure in the Intake Manifold, thus relating the engine Load to the ECU.  There is a lot happening in this precision sensor which is covered on a separate page.

See also: 


Bosch D-Jetronic Circuit.  Sheet 2

Sheet 2.  Throttle Position Switch (TPS), Acceleration Enrichment (AE), Fuel Pump Control (FPC), and Cylinder Temperature Compensation (CTC)

TPS:  (Additional info in Reference Information, TPS below!) (See also:  TPS Additional)

The TPS is misnamed!  It actually does NOT give Throttle position information back to the ECU!  What it does give, is Idle, and Throttle opening (only, not closing!) info, which is then interpreted as a demand for acceleration, so ECU generates and adds "Enrichment Pulses".  There is a lot happening in this component(!) Idle switch, a "Drag Switch", plus sliding contacts which are fed back to the ECU.  The sliding contacts on the Printed Circuit Board (PCB) conductors can eventually wear the PCB contacts, particularly if not periodically cleaned and lubed.  Eventually, this wear results in symptoms of an occasional misfire during otherwise steady RPMs (like at highway cruise).  ...or maybe not!  See TPS Update below!  

The TPS tells the ECU what driver throttle inputs are! 

More modern TPSs eliminate the inherent wear weakness of a contact technology with non-contact (magnetically or otherwise coupled), technology, but we D-Jet owners are kind of stuck with them...and they are No Longer Available (NLA) from Volvo/Bosch.  Luckily, and since there are a significant number of vehicles out there which were fitted with the D-Jetronic System, some sharp, enterprising individuals are producing quality reproduction PCBs, allowing TPSs to be rebuilt.  See below  Reference Information, TPS Additional below!!

TPS Update:  A separate detailed study of the TPS, and how it can cause the Miss at Cruise  MaC symptom, particularly including interaction with the ECU Enrichment circuit, is in progress.  Besides being misnamed Throttle Position Switch (it doesn't even sense Position(!)...only Idle and when Acceleration is called should therefore more correctly be named:  Idle and Acceleration Sensor) it is already clear from preliminary findings, that wear of the PCB conductors is much less of an issue (and may not even be the cause of MaCs) than everybody (including the author) has previously thought!  [In progress and not yet on-line:  Bosch D-Jetronic TPS and Miss at Cruise (MaC) Investigation

What is unquestionably a good idea, is periodic maintenance of the TPS!

Throttle Position Switch Suggested Maintenance using Deoxit D5: 

TPS Conjecture:

My posting to a Swedespeed Thread:  My Volvo/ Throttle Position Sensor woes.

"There is no bridging which occurs between the Comb is just not possible, as the sliding contact is not anywhere near wide enough (including with wear), and it would require a ridiculous amount of "redepositisation of plating" (possible I suppose, but only with ZERO switch cleaning and lube maintenance, [and massive wear and resultant arrant conductive particulates], and then I still strongly question and doubt any negative effect on inputs of the R/S Flop)...the sliding contact strictly provides Reset/Set inputs to the R/S Enrichment Flip-Flop, which is HIGHLY bounce resistant (including of contact bounce if that were to occur, as the Flop would be locked out by the first input and COMPLETELY ignoring ANY subsequent triggers), [Reference: The Edge Triggered Flip-Flop]. ...and explanations of "arcing" of the comp contacts circuit, limited to a mere 18mA, resistive, not inductive(!) has me laughing out-loud!  I consider both of these explanations as good ideas by guys who know just enough electronics to come up with non-substantiated conjecture! "


Setting the Idle on a D-Jet:  ...the Throttle Stop is NOT the Idle Adjustment, because of the way it interacts with TPS. 

More details at Link to separate Sw-Em Tech Notes:  D-Jet Idle Adjustment


Idle Adjustment Screw and Locking Nut in Throttle Body. 

Fuel Pump Control:

FuPu control is a timer circuit, which is powered whenever ECU is powered up, but will "time-out" after two seconds or so, if it does not receive pulses from the Speed Compensation Circuit (which in turn gets triggers from the Distributor Contacts located on Sheet 1.).  I've heard this action be referred to a "priming" the Fuel Rail with pressure, but I don't like this description so much...I prefer to call the action "timing-out" if the Ignition is turned ON, but the starter is not engaged, and one hears the FuPu come ON, then go OFF again!  In this way the Fuel Pump is disabled in case of an accident or engine OFF, so that it does not pump fuel, possibly into the open.   

See also:

PLACEHOLDER FOR additional material.

Cylinder/Coolant Temperature Sensor:

From Dr-Djet's page:

From a posting by Fran Krause:  [Unconfirmed by the author, but it looks like Mr. Krause has done good research to substantiate equivalency!]

"I noticed that the coolant temperature sensor is hard to find for the B20E & B20F. I also noticed that the Bosch 0 280 130 014 temperature sensor (fifteen bucks) has the same resistance curve. If you file the threads off and then re-thread it with a M10x1 die, it actually fits. The terminals are .25mm off, so the old d-jet connector is a bit tight. Surprised this actually works. "

Fran Kraus pic, permission requested.

OE Cylinder/Coolant Temperature Sensor (NLA) and functionally equivalent Bosch 0 280 130 014 sensor solution.



Bosch D-Jetronic Circuit.  Sheet 3

Sheet 3.  Engine Speed Sensor (ES), Engine Speed Compensation (SC), Pulse Width Multiplier (PWM), Idle Mixture Adjustment (IMA, including  Idle CO adjustment Potentiometer, after '71), and Idle-Cold Mixture Compensation (ICM)





D-Jet Wiring Interconnection Diagrams as integrated into the Volvo vehicles.  The big difference is between early and late implementation is the manner of control of the Cold Start Injector/Valve, so two circuit excerpts from the remaining vehicle wiring diagrams are both shown here: 

'71 1800E Fuel Injection Wiring Diagram:  Early system, with Cold Start Relay for mixture enrichment, controlled by ECU pin 2 ('69 -'71), in-turn, controlling Cold Start Injector/Valve: 

Excerpt from '71 1800E wiring diagram with Fuel Injection system connections and components. 

Complete '71 1800E wiring diagram here:


'73 1800ES Fuel Injection Wiring Diagram:  Late system, not with a "Cold Start Relay", but a completely independent Thermo-Time Switch for control of the Cold Start Injector/Valve and mixture enrichment  ('72 -'73):

Complete '73 1800ES wiring diagram here:


Thermo-Time Switch  (TTS)

In the late version of the D-Jet, the Cold Start Injector was controlled not by the ECU by way of the Cold Start Relay, but by a completely separate and independent Thermo-Timer Switch.  As can be seen in the '73 1800ES Fuel Injection Wiring Diagram above, this component as well as the Cold Start Injector (also:  Cold Start Valve) are powered during Starter cranking, which also powers an internal heating element on the bimetallic element for a combination of Time and Sensor (engine block) temperature dependent operation, to enrichen the mixture.  Note that in this way, the Cold Start Injector only enrichens during cold AND cranking!

If the engine is already warm, this function is disabled during anything warmer than 35 Deg C (95 Deg F).  The TTS also self-heats to prevent excessive enriching (aka:  flooding!) with repeated Starting attempts in rapid succession.  

A Thermo-Time Switch has been cut open to allow inspection of its internal construction. 
Picture source: Corrections made Jun 2024! 
[Apparently, this component was also used in the K-Jetronic Continuous Injection Systems, which is what the linked thread is about.]

Notice the G and W terminals on this component are of a different size...this is for good reason...they may not be interchanged!
I have also made corrections to the above picture, after it was pointed out that the G and W terminals and the descriptions were swapped, in a Swedespeed thread (  ).  The connection shown in the wiring diagram above is correct.  Any observant reader finding errors is invited and welcome to point them out (accompanied by appropriate substantiating material!).   

Further good info on the TTS (also source of this picture, showing mounting location at rear of engine, above Oil Filter):

Thermo-Time Switch (TTS) in Situ. 


PLACEHOLDER FOR Cold Start Injector/Valve material.


D-Jet Fuel Handling Components:  The observant will notice the D-Jet fuel system is a continuously circulating system.  Fuel Pump charges Fuel Rail with pressure, and this is precisely regulated to the 28-30PSI required by the D-Jet System.  The Fuel Pressure Regulator keeps Fuel Rail Pressure constant even with the highly variable demand of all driving conditions, and routes any supply amount beyond what is needed, back to the Fuel Tank via the Fuel Return Line.  This system strategy also keeps the (wet) FuPu cooled by the continuous flow of fuel, and all of this flow is through the generously sized Fuel Filter.  Notice there are differences in Tank and related plumbing by year of manufacture.  


Fuel Rail Pressure and Troubleshooting D-Jetronic issues:  One of the most important parameters of the D-Jet (and any other Fuel Injection System for that matter!), is the system Fuel Pressure.  When pressure is constant, as well as the (injector) orifice it is being metered through, the duration Injector is open is the remaining variable by which fuel amount can be very accurately controlled.  Pressure is set and regulated by the Fuel Pressure Regulator.  This component keeps the pressure in the supply rail (Fuel Rail in graphic) to all Injectors at a constant 28-30PSI even with varying fuel demand.  The FPR does this with a spring controlled diaphragm routing unused fuel back to the Tank.  This type of FPR is sometimes referred to as a "Dump Type Regulator"...this is in contrast to a more typical Regulator which dead-heads the supply stream (low flow) during low demand.  Bosch engineers preferred to use the dump type Reg so they could have continuous flow through the fuel supply system.  This allows continuous filtering as well as cooling of the "wet" FuPu. 

Fuel Pump


Copy of my comments to a Brickboard thread: 

"Of course, the first thing I would suggest Mike check for is to listen for Fuel Pump charging the Fuel Rail when turning ON the Ign Key...his no-start could be as simple as FuPu Fuse being open from a poor contact at the Fuseholder (a known common issue for owners which haven't treated all of their fuse-ends with ACZP)...I like to start by checking the simple things first..."

Link to Brickboard Thread detailing Fuel Pump variation (by model year of production) of plumbing fittings (two port vs. three port):

Fuel Pump Function, including Time-Out, and Loud-Function: 

Copy of my clarification to thread:  1972 pv1800es [Although there is no such vehicle!]

(FuPu Time-Out)  FuPu is under control of the D-Jet ECU, by way of (ECU Pin 19) and FuPuRel...but to answer the runs on initial Ign ON (which charges Fuel Rail to allow Starting), but if Starting process does not immediately follow (which results in "engine running pulses" from Distrib contacts to ECU), it times out and shuts OFF FuPuRel and consequentially FuPu (this is a crash safety requirement).  See also:

Once Engine is running, FuPu is powered continuously, charging Fuel Rail, with FPReg keeping rail pressure at a constant 28-30PSI (independent of demand, with no thermal or Manifold Vacuum/Boost input or bias like in some later FI systems), dumping whatever in not being needed/used as a function of engine demand, back to the Tank, but is typically quiet enough not to be heard over engine noise...

(Loud FuPu)  If FuPu is noticeably loud, it can be due to a FPReg operational failure in that the Tank Return is not functioning normally (including blocked), such that the (positive displacement) FuPu is "dead-headed" or pumping into a blocked tube or system where no fuel is allowed to flow, the overpressure Bypass Valve integral to FuPu [which is normally and maybe its entire life(!) inactive, and not called upon!] opens and bypasses the blocked path, and this results in an unusually noisy FuPu. As the FPReg normally does all the regulating and fuel circulating, this Bypass Valve is normally not functioning...its' noise typically indicates something is amiss.

Rattling noise at Fuel Pump:  

My response to a posting asking about a "rattling noise that is not drivetrain related" on an 1800E:   

"Rattling noise at Fuel Pump can also be due to its internal bypass operating (cycling, with chattering sound!) to relieve over-pressure because FPReg is not working right, OR Fuel Return Line is blocked...ANY blockage or failure in circulating fuel system can cause this! Remember, fuel MUST circulate, and NOT by FuPu Over-pressure Valve (that only operates as a secondary pressure relief, when something else is NOT right!).

I'd recommend you check Fuel Rail Pressure...also open Fuel Return line to Tank to assure it is flowing when FuPu is powered. Observe open fuel/fire safety!  "


Non-functioning Fuel Pump?  See also:  Marked up Wiring Diagram for D-Jet Troubleshooting


Fuel Pressure Regulator

Because the Fuel Rail Pressure is so important, it should be verified to be correct as one of the first items to be checked after Fuel Pump is verified to be functioning, and this is also how it is presented in the referenced Fault Tracing Manual


Source of original info:  Factory Manual for 1971 1800E, amended by the author.


Framecapture from an Andy Somogyi video, and used with his kind permission: 

My responses to a post about testing and trusting function of the Fuel Pressure Regulator. 

"I can't agree that the diaphragm is rubber sorry.[...suggestion from other poster.]

I'd also be careful about blowing shop air (pressure of which can be in excess of 100PSI!) into that FPReg. Max pressure from the Fuel Pump is 60PSI...[..he later advised that he had indeed decreased air pressure to 60!]

[Related anecdote, paraphrased.] There was a directive in the jet engine service industry (Pratt& Whitney) NOT to use WD (which sucks anyway IMO!), and get it off the factory floor, because it was found to have "negative affects" with dissimilar metals (sorry I have no further details, I got this second hand from Al V. in the industry), who also runs a vintage dragster...he says that in the industry, they were instructed to use Aero-Croil for penetrating jobs, and Tri-Flow for lubing and storage jobs...and that is what he started doing on the dragster...on ALL fuel contact components from Fuel Pump to (mech) injectors...he said he has done this for 15 years without any white corrosion products growing on surfaces, and no reportable negative effects. That's good enough for me! I love Tri-Flow anyway and recommend it for light lube jobs, but I haven't until now recommended it for fuel contact areas...I guess it just gets flushed away next time fuel comes along, and consumed in the problemo! See: Cheers!

Additional: I've been thinking about this (the possible failure mechanism) a bit more...FPRegs are known for failing stuck so they don't return fuel to the tank...this causes the FuPu to effectively pump into a blockage (deadhead) and its internal overpressure bypass valve must open to relieve the overpressure [and this results in unusual noises]...I haven't heard of any "leaks" failure mechs, but the case is swaged closed...I suppose leakage could occur an idea, the case could be cut open on a retired FPReg and a detailed inspection could be preformed...and a resourceful machinist/fabricator could certainly come up with an external clamp to hold one back together and sealed after an internal inspection/cleanup...I believe FPRegs are NLA..."



Measuring Fuel Rail (Fuel Pressure Regulator output) Pressure:  Since it is such a critical parameter for a properly functioning D-Jet system, it  must be one of the first things checked for proper operation!  I have used an Oil pressure is a bit "rustic", and not particularly accurate and I would certainly not use it to adjust FPR output pressure, but it was plenty accurate enough to show fuel pressure was dropping into the cellar under demand (for instance as later confirmed to be the result of a rust-blocked In-Tank Pre-Filter, but that's a story for another day...). 

Caution:  The Fuel Rail will hold pressure even after the Ign is turned OFF and Fuel Pump stops charging it (the pressure will then only slowly discharge back to zero)...the point is...when troubleshooting injection issues which require opening up the Fuel Rail to insert the Pressure Gauge/Manometer or for any other reason, use EXTREME CARE to be ready for, protect yourself from, and catch possible/likely squirting fuel, and observe fire prevention practices!  ...and having a fire blanket and extinguisher at hand when working with fuel in the open can't hurt! 

Relieving Fuel Rail Pressure:   Typically, Fuel Rail pressure will bleed down on its own after ignition is OFF, but the time it takes for this can vary widely.  It is best and safe practice, in preparation for opening the fuel plumbing and working on fuel handling components, to simply pull the Fuel Pump (Fuse5 on E and ES cars) while the engine is idling, and let the engine die of fuel starvation (...then shut OFF Ign!), before opening the supply lines.  This assures that there is no residual pressurized fuel present. 

Early configuration (no Prefilter internal to Tank), so FuFi (2 Port, internal Bypass) is located before FuPu!

Since the Cold Start Valve is out of the picture and unused in a warmed up engine, the Fuel Rail Pressure can be measured by disconnecting the CSV supply line from the CSV, and plumbing it to a pressure gauge (Manometer) capable of 60PSI minimum.  While the normal operating pressure for the Fuel Rail is 28-30PSI, with a FPReg failure it can soar to the maximum output of the Fuel Pump (around 60PSI, which is when FuPu internal Bypass Valve opens to prevent deadheading the pump.  This is typically accompanied by a noisy/rattling FuPu.  See above!  Fuel Pump...Loud-Function ).  



Fuel Rail Pressure Drop due to Feed Restriction

If a drop in the Fuel Rail Pressure is observed at any time when engine is supposed to be running normally, the reason must be located and corrected before there is any chance of expecting the D-Jet Injection System to function correctly!  Any number of electrical things which interfere with proper action of the Fuel Pump and delivery can cause this, (for example, any electrical issues with the FuPu power supply), but they are the subject of discussions elsewhere.  

What is considered here is restriction in the fuel supply plumbing will cause a Rail Pressure drop (the electrical analogy being the restriction acts as a Dropping Resistor in the fluid flow, which decreases Voltage/(Pressure) downstream. 

A not totally uncommon and condition which unusual symptoms...!  I have heard of it several times, and have actually experienced first-hand [no fun!]...a rust particle clogged Fuel Prefilter causing this on an 1800ES (apparently the Fuel Tanks are susceptible to internal rusting, depending on weather conditions and moisture presence in Tank)...and not just the external FuFi...but also a clogged Prefilter inside the Tank.  Since this Prefilter is in-line with the fuel feed to the Fuel Pump.  When enough rust particles collect on it, it can/will act as enough of a restriction in the flow path, to at the worst-case, completely choke off the fuel demand (not even sufficient for idle!)...symptoms are engine being able to start, and (maybe) idle, but not being able to throttle up or make power. 

If we happen to already be troubleshooting and monitoring Fuel Rail Pressure (as we know this is THE critical parameter for the D-Jet), Fuel Rail will be observed to be dropping into the cellar (but FuPu is getting electrical power and running), and no amount of changing the external FuFi helps, BUT simply turning OFF Ignition and engine, and restarting, seems to cure it...for a while, when the whole somewhat baffling process repeats...engine wont throttle up or totally dies because fuel-rail pressure has dropped, but pressure is fine at restart attempts, engine runs OK, but after a certain amount of normal running, the issue repeats!  This can be mighty frustrating until properly sorted! 

Looking up at the ES Tank Prefilter.  Access requires draining the Tank, then removing the Tank Sumpplug,
which it is located right above.  When removing the Sumpplug, any debris which has at one time or another
been sucked onto the Prefilter, will have dropped into the Sumpplug (which is cup-shaped), and can be inspected.  

Excerpt from a posting of mine, in response to D-Jet failure with the aforementioned symptoms: 

"Fuel Rail pressure is one of the (if not THE) most important parameters for a properly functioning D-Jet...and monitoring when the symptoms occur will quickly tell you if the issue is due to I posted in the linked VOC Forum [ ], I had a hellova time with it also due to Prefilter clogging with rust particles...

To monitor Fuel Rail pressure, I plumbed an oil pressure gauge in, inplace of the Cold Start Injector, and duct taped it next to the fresh air vent so I could monitor it while driving and with high demand [higher anyway than idle, where the issue might not occur or be slow to manifest itself!]...and sure 'nuf...the pressure was slowly dropping until engine couldn't run anything above idle...but turning it OFF and waiting a minute or so (for particulates to fall off Prefilter, and it was alright for a while again...Lather Rinse Repeat!).

If you also confirm low Fuel Rail pressure, first change [external] Fuel Filter, and inspect what it has captured...

Prefilter (aka Sock, maybe from a manual, or Volvo Partsbook) is located above 3/8" square[drive] Sumpplug, where the particulate falls and can be cleaned to be done with a near-empty Tank (less fuel to deal with)!

See also: Good Hunting! "

I have added the Pre-Filter, which protects the precision Fuel Pump, to this diagram of the Fuel Handling Components! 
In this later configuration with Internal Prefilter, the Replaceable FuFi is located behind the FuPu!  The observant viewer
will also notice the ("three-port") FuPu Bypass connection to Fuel Return line to Tank. 

Note: The Prefilter is not present in all D-Jet equipped models!  A good place to refer to, to confirm presence would be the exploded assembly diagrams and Parts Listing for a given model, on the site.  [...unfortunately, I was not able to find it there, and I do recall having seen a factory diagram at some point!...need to research this further!...if you can help, please contact the author!]

On late models '72, '73, where the Prefilter is present (also on factory replacement Fuel Tanks), it is my understanding that the replaceable FuFi external to Tank should be plumbed AFTER the FuPu, since the Pump is protected by the Prefilter.  See also:  Injected Fuel Tank Plumbing, 3 Port Fuel Pump 



Fuel Injectors

Chris Mullet pic, repost permission requested.

Here is a basic Injector Test, presented by Chris M, rather brilliant in its simplicity and safety! 
It does allow observing 8 of the 10 important D-Jet functions...from fuel supply, to Injector spray
pattern, to comparing relative amounts delivered to each cylinder, and much safer in that fuel is not
sprayed into the open.  [There is little more dangerous than atomized fuel, just looking for a source of ignition! 
bserve fire prevention practices! ]


Chris writes in this thread:  ):  "I mainly used clear tubing so that I could easily compare the volume of fuel flowing through each injector. This was after running them through a DYI back flush process.  [See also:  Injector Cleaning below!] Whether the flow rate was to spec or not I had no idea, but I figured if all four were equal, or "close" to equal, then there was a good chance the flow rates were close to spec. Being able to witness the spray patterns turned out to be a bonus I hadn't thought about.

Setting up for the test, I pulled the distributor out of the engine, removed the cap, and re-connected the trigger points connector. Turning the ignition on activated the fuel pump and D-jet system. Then I spun the distributor rotor as fast as I could with my finger - spin, spin, spin, - and watched the injectors spray into the clear tubes. With no vacuum being applied to the MAPS sensor the system calls for a high fuel flow rate through the injectors. I sucked on the MAPS hose to simulate different engine loads along with propping the throttle plate open or closed while spinning the distributor resulted in varying amounts of injector flow. As I recall, quickly opening the throttle alone resulted in an "acceleration shot" of fuel from the injectors. It was somewhat interesting. So now I was, in effect, performing a poor man's test of the entire D-jet system."

[Note:  Abbreviation for Manifold Absolute Pressure (MAP) sensor has been corrected to Manifold Pressure Sensor (MPS). 

See also:  D-Jet Manifold Pressure Sensor]

See a detailed report of the use of Chris Mullet Fuel Injection Test Method (CMFITM) in conjunction with a Remote Start Switch.   He disabled the Ignition, and used a Remote Starter Switch, to turn engine and provide Trigger pulses to ECU from the FI Trigger Points in the Distributor base, and since the FI sys was normally powered, it could generate the necessary pulses to fire the Injectors:

Remote Start Switch or "Starter Switch" from Battery to Term 50 on Solenoid, is simply a high current momentary switch, which can be activated while under the hood and observing the Injector action (I install such switches permanently under the hood and call them a "Service Switch").  Such a switch can also be useful when performing other service tasks (like priming the oil system, or compression checks...).


Injector Cleaning:  

See separate page:  D-Jet Injector Maintenance and Service Notes


Fuel Line: 

Friendly Safety and Reliability Tip:  Inspect your fuel lines, both hard and flexible, and if you find any evidence of leakage or surface discontinuities, replace the offending lines with the correct lines.  Flex lines must be high pressure and ethanol qualified!

Tom Neal Pix used with his kind permission:

Fuel-Line at the Fuel Filter, clearly weeping and with cracks in the line apparent is in IMMEDIATE NEED of replacement!  Don't leave this condition!  Remember, there is pressurized fuel in many of them!  Inspect Fuel Lines periodically and fit ONLY first quality high pressure rated line! 

Excerpt from my response to pic of fuel leak and question as to which hose to use: 

"I don't like the unprotected copper tubing so much. [Tom subsequently reported it was in-fact CuNiFer that's OK!]  I would expect to get 5-10 years out of new ethanol compatible hose, but a periodic inspection can never hurt!

If downstream from Fuel Pump, make CERTAIN it is high pressure qualified!!  Cheers

Edit to posting:  If it doesn't specifically say high pressure qualified (like that shown in picture!!) [or "Suitable for Fuel Injection" or equivalent], it is NOT, and NOT SUITABLE for high pressure downstream of could however be used for (nonpressurized) fuel return to tank, or venting!  Remember, on D-Jet cars, Pressure can be as high as 60PSI downstream of FuPu, and upstream of FuPressReg under certain conditions!"



D-Jetronic Service Tips and Techniques (which deserved to be captured, but didn't fit under the individual FI Component categories):

Vacuum Leaks: 

See also separate Tech Article:  Vacuum Leak at FI Intake Manifold Plug


The typical and simple way and first test for vac leaks is with an engine in a normal operational state and at idle, to spray Carb Cleaner in all of the hose and component joints and possible gaps, and note any changes in RPM.  If any air is being sucked in at compromises in joints, it will also suck in the combustible carb cleaner raising the RPMs, thereby giving itself away. 

The alternative test a service place might perform, (engine OFF, Smoke Generator required!) is with the filtered air intake blocked off, and a smoke generator charging the entire intake tract, so that smoke would be pushed out any unexpected intake tract discontinuities, leaks again giving themselves away! 

This is not a Grinch Stole the Intake Manifold Joke!

Pic of smoke test with glove over Fresh Air Intake to seal the fresh air orifice.
Dave Morrell pic, permission requested.

Vacuum Leaks can cause Idle Cycling from 1500 to 700:  Thread:

(False Air [not really, because the MPS would still sense the additional air and cause the system to deliver the correct fuel amount, but the RPMs would not be under control of the driver!] or Vacuum Leak)

A fine explanation by Dave Morrell: 

"The cycling from 700 to 1500 is definitely a vacuum leak. The computer is looking at input from the throttle position sensor and finding it at idle and cutting off the injectors at 1500 rpm. When it drops down the computer starts the injectors up again. You can test this by unplugging the throttle position sensor and starting the car. Without input from the TPS, the engine will rev to whatever level the vacuum leak allows. I had this same problem on my 70e when I bought it. Skip all the cheap ways of detecting a vacuum leak and just buy the $160 smoke machine on Amazon. It’s well worth it and you’ll see every leak in your system. My main leak turned out to be injector seals. You’ll need a rubber/latex/nitrile glove to stretch over the intake opening to hold the smoke in. The adapter that comes with the smoke machine doesn’t fit the B20 intake very well. You cover the intake with a glove and attach the smoke machine to one of the other vacuum line ports on the intake."

Additional Explanation by James Maddison:  

"I think Dave Morrell provided the best explanation but it's good to understand exactly what's going on and dividing the problem into 2 parts. the reason for the cycling is that the way d-jet works is if the throttle is fully closed a switch turns the computer to idle mode and above about 1700rpm [AND with Idle contact of TPS closed] it cuts out the injectors as normally this would be achieved when driving the car and releasing the throttle and as the revs drop it brings the injectors back in again at around 1100 rpm for a smooth transition to idle but with no load it can dip quite low and then start revving up again hence the cycle. What's causing the high idle could be an air leak as many people have mentioned or even just an incorrectly adjusted idle. start by adjusting the throttle stop as per instructions then see how it behaves. long story short, i do also think there's a leak somewhere but it's worth knowing what's going on to understand why the car is doing what it's doing and thus how to fix it."


Auxiliary Air Valve:  

The Auxiliary Air Valve (Bosch PN for valve fitted to Volvos:  280 140 013 ) is a thermal element powered valve which senses the temperature of engine Cooling System by means of a wax-filled sensing bulb not unlike a Cooling System Thermostat, and when cold, allows a small amount of air to bypass the throttle, thereby raising the idle during warmup.  A common failure mode of this valve is the movable element binds up (I suspect Galvanic Corrosion of the alu valve assembly bolted to the iron block(!), not unlike what happens with an alu Radiator, see:  Galvanic Corrosion in the Cooling System  ).  Depending on the position they bind up in, this can lead to a perpetually high idle (when open and allowing bypass), or poor warmup idle (needing the driver to feather the throttle to "keep engine alive"), both tough to ignore.

AAV disassembled to show construction.  The Air Bypass Orifice shape varies with engine manufacturer the AAV was intended for. 

A separate Tech Article is in progress, but again, there is a lot of engineering which has gone into this component, so it is not yet the meantime, I just had to show this manual but nonetheless brilliant alternative: 

Aux Air Valve Alternative: 

[I saved this in my notes when I first saw it, but hadn't added it here (yet), wanting to first add some part numbers, sources and further details...but since the AAV is NLA, and an owner might need a solution NOW, I figure it's time...]

For those that value function over a stock engine compartment, or wish to keep a working fast-idle which does not require arranging for a mortgage to buy a replacement valve, here is a good working manual replacement using a Heater Control Valve [Yes, you read right!  There is nothing that says this valve can't control the flow of air instead of Coolant!]

From the let's-just-get-it-done is a modestly priced generic Heater Control Valve, mounted in the general original location and manually controlled from the dashboard with a Bowden Cable...a brilliantly simple solution! 

Pic by Paul Cassell in the UK, of his 1800ES, and used with his kind permission. 

Manual Aux Air Valve solution which earns high points for creativity and effectiveness of solution!


Chassis Connections for D-Jet: 

Without a good chassis connections for the D-Jet, where one should normally be, noise and voltages can be added/subtracted from Sensors and Injectors, (see:   ) this can wreck havoc with the otherwise highly-reliable Bosch D-Jet system, giving erroneous inputs to the ECU, and messing both directly and indirectly with outputs as well, resulting in the strangest symptoms to frustrate even the best troubleshooter!

That's why an experienced troubleshooter will often start his observations of D-Jet equipped vehicle (ANY FI vehicle for that matter!), with an inspection of chassis connections. rather than have them clean up and make right any questionable connections (at $100/hr...yipee!), might it not be a better idea to take care of these things yourself?...hell, he might not even be a reader of the SW-EM site, and be aware of the benefits of long-term protections and corrosion invulnerability provided by ACZP!

Tip:  BEFORE taking your misbehaving D-Jet equipped car to an expensive service provider (hopefully not one whose first question is:  Where's the OBDII port?), inspect and SW-EMnify (...another verb variation of rootword SW-EM, Ref:  ), all the chassis connection from the Batt, to the chassis to engine, V-Reg, (2) FI Control Relays, to all obvious D-Jet wiring, then move on to not-so-obvious D-Jet wiring!  You might just reward yourself with a well-behaving D-Jet!  ...but if symptoms persist, you can send the car to the $100/hr guy! [...but he still won't be able to talk to the computer by way of OBDII!  With D-Jet, YOU are the on-board diagnostic...YOU need to remember under which operating conditions symptoms occur, and consider that during troubleshooting!]  


(One of the) crucially important chassis connections for the D-Jet Injection System! doesn't take a $100 an hour mechanic to clean and reconnect these connections (with ACZP) bringing them to a Condition A1, and eliminating them as suspects when a D-Jet car is misbehaving! 



Reference Information: 

Service and Troubleshooting Documentation: 

Marked up Wiring Diagram for D-Jet Troubleshooting:

The Green labeled power nodes are rudimentary electrical checks, but critical for function of the D-Jet!  

Fuel Pump is powered by FuPuRel which is in turn under control of the ECU...but don't forget Fuse5! 

My response to a posting asking reporting a non-working Fuel Pump after FuPuRel replacement: 

"Why was Fuel Pump Relay replaced? Did FuPuRel not pick before?

If it clicks now, that's a good beginning...FuPuRel is under control of the ECU...but if FuPu is still not getting power, check (and rotate) Fuse5! If this corrects issue, clean to shiny metal, ALL FUSES and their holders, and reinstall with ACZP. This is a not uncommon problem after 50 years, but would not and NEVER occur if owners just followed my advice and made a gas-tight and virtually corrosion-proof connections at their fuses...yes, I said "would not and NEVER occur"!

When will they learn...?

...and don't toss your old FuPuRel, because it's fine, but send it to me, and I'll send you the ACZP! Good Hunting"


See also:  Fuel Pump Function


Link to very good troubleshooting guide:

Another excellent source of general info on the Bosch Injection System from the early D-Jetronic (electronic) to K-Jetronic (mechanical - constant Injection) all the way to the later variations of the Motronic engine management with Lambda exhaust sensing to allow the system to function closed-loop, is the book:  Bosch Fuel Injection & Engine Management by Charles Probst,  published by Robert Bentley Publishers  SB  ISBN 0-8376-0300-5.  The book contains theory of operation, development, and practical troubleshooting information.  An excellent reference for D-Jetronic, K-Jetronic equipped and also vehicles with later injections systems by Bosch. 



Phil Singher's excellent general write-up on Bosch D-Jet: 


Part Numbers:  Source?


Throttle Position Switch (TPS) Additional: 


Early type TPS easily recognized by the radial angle of comb contacts, and separate drag and Idle (a) switches.  If this was a picture of an actual switch, discrete wires between I/O connector and innards would be evident.  There are no discrete wires in the later switches...this makes them simple to differentiate.  

Translation (Credit?...looks like one of those on-line translators...lots of gobbledygook, and tough to understand...I should rework this sometime to improve understandability): 

3.4 Throttle Valve Switch

Fig. 7 shows the throttle valve switch in the plan view with cut cover. The throttle idle micro-switch of forming contacts a by the lever c connected rigidly with the throttle valve wave with closed throttle valve are operated. The disk b is concentrically arranged to the hub of the lever c. One wave feather/spring between the disk and the housing bottom provides for a defined friction opposite the housing. When opening the throttle valve (in the picture against the clockwise direction) the disk b is held by the friction first, the lever c moves against the contact record d drags switch and closes this. After a small overflow route for the contact record dashed a drawn driver of the lever c carries the disk forward b. Thus the two slide with the disk b firmly connected pickup shoe on the contact plate e. With closed contact record d the teeth of the two edge contacts in the change are connected electrically with the continuous pickup shoe path. Switching a comb on the other hand has the advantage in relation to easy switching on and off that during uncertain contacting or bouncing the contact no additional enrichment impulses in the controller are released. 


Adjustment of the TPS

The following good info is copied from Volvoniacs, and still needs translation:  [My highlighted comments and clarifications added.]

Er sitzt an der Drosselklappe und gibt ein Leerlaufsignal (für Schubabschaltung) und Drosselklappenstellungssignale (nicht absolute Stellung, sondern nur Änderung der Stellung, und das bei weiterer Oeffnung des Drossel,  bei Schliessung des Drossel sind die Kontakte des Schleppschalter geoeffnet) in über ein Potentiometer (falsch! kein Poti!) an das Steuergerät.gleichzeitig auch Drosselklappenstellungsgeber .ZV kontakt 1 (9 1/2 Impulse) .ZV kontakt 2 (10 Impulse)

Einstellung Drosselklappenschalter

Das Ohmmeter zwischen die Klemmen 14 und 17 anschließen. Der Wert soll 0 Ohm (Durchgang) betragen.

Bei "unendlich" den Drosselklappenschalter neu einstellen, sonst gibt es kein Leerlaufsignal und damit keine Schubabschaltung. Wenn trotz korrekter Einstellung kein Leerlaufsignal kommt, muss der Drosselklappenschalter erneuert werden. Bei etwas Gasgeben muss das Leerlaufsignal weg (anzeige unendlich) sein.

Achtung! CO im Leerlauf kann nur eingestellt werden, wenn das Leerlaufsignal durchgeschaltet wird.

Beim Fehlen des Leerlaufsignals kommt es auch zu erhöhtem Kraftstoffverbrauch, da die Schubabschaltung nur mit Leerlaufsignal und über 1800 U/min arbeitet.

Drosselklappenschaltersignal 1 (9 1/2 Impulse) und Drosselklappenschaltersignal 2 (10 Impulse) können nur mit der "Blauen Bosch Kiste" geprüft werden.

Der Schließwinkel der Auslösekontakte unten im Verteiler ebenfalls.

Als letztes CO einstellen.

Sollwert: 2% CO

Eingestellt wird ab Baujahr 1971 am Poti am Steuergerät, vorher (1800 E mj 1970)ist das Poti nicht vorhanden.

Das Poti ganz nach rechts und dann zwei Klicks nach links drehen, die Kontrollmessung muss jetzt 2% CO ergeben. Wenn nicht: Nach rechts = fett, nach links = mager.

Leerlaufdrehzahl einstellen

B20: Die Kontermutter der konischen Schraube unter dem Lufteinlass vorne am Ansaugkrümmer unten aufkontern.

Schraube reindrehen = niedrigere Drehzahl

Schraube rausdrehen = höhere Drehzahl


Wenn die Einstellschraube bis zum Anschlag reingedreht ist und die Drehzahl trotzdem zu hoch ist, kann es folgende Ursachen haben:


Den Drosselklappenschalter lösen, die Anschlagschraube entlasten und die Drosselklappe schließen. Dann die Anschlagschraube beidrehen, bis die Drosselklappe anfängt,sich zu öffnen. Dann die Anschlagschraube eine HALBE Umdrehung reindrehen Dann den Drosselklappenschalter einstellen.


Ruckeln bei Konstantfahrt Konstantfahrruckeln liegt normalerweise am Drosselklappenschalter, alte Ausführung mit geschraubtem Deckel. Diesen dann erneuern.  Es kann aber auch mit der neueren Ausführung (Deckel nur geclipst ) auftreten.  In diesem Fall sind die Widerstandsbahnen [...this is poor use of terminology and could lead to misunderstanding...Widerstand means Resistance, and there is no variable Resistance here like a Potentiometer, only Contact/No-Contact areas.  Ron] durch den Läufer und durch Spiel der Drosselklappenwelle verschlissen.  Vor der Erneuerung des Drosselklappenschalters die Buchsen und Drosselklappenlagerung erneuern.


More Links at the Volvoniacs on the TPS:,15/#last

D-Jetronic DKS Drosseklappenschalter:


Reproduction Parts for D-Jetronic:  (links/availability not checked as of 10/2015)

Neue Stecker und Gummitüllen für D jetronic B 20 E/F Robert Bissler bei

Nachproduzierte Platine Drosselklappenschalter . bei office bei v



Throttle Switch 039 906 111 A 0 280 120 032 2.0L 1973 - 1976 No Longer Available new. If you go to , and look up user "davesprinkle", he's been fabricating a kit to replace worn TPS circuit boards, so that you can rebuild your TPS.


Replacement PCBs for TPS from: 
I have not had one of these in my little hands for a critical inspection, but they look good from where I'm sitting. 

Lube with Deoxit D5 at installation to prolong life and reduce wear like this (this is a representative picture showing what happens when a PCB conductor gets worn/scratched...but looking at the ratio of conductor to insulator width, it doesn't look like it's from an actual TPS):

Picture Source:

Here, although not perfectly clear, at Red, damaged gold plating and metal displaced by continuous wiping of the moving contact is evident.  Lubrication would delay/reduce such displacement!  I'll try to get an even better picture: 


Comb contact, showing evidence of wiping contact, but practically no wear. 
De-Oxit D5 would go a long way to lubing and protecting this area to delay wear.



Link to D. Farrington pictures:


Baaad Info:

Throttle Position Sensing Switch

In exercising the search function, detailed info on the TPS is sparse, and in the case of this publication, even highly imaginative...and incorrect, and not elementary my dear Watson!  It is simply not possible for the sliding contact or alternate comb contacts to "begin to arc as the throttle is held at a steady position"...resistive voltage divider networks for T904, T905 (Throttle Flip-Flop, see sheet 2 above) limit current and voltage to a miniscule level which would never be able to produce an arc!  Lack of lubrication between the board conductors and never-ending motion of the sliding contact can cause wear (this is where the correct lubrication comes in), but no arcing or carbonization ever takes place!         


TPS related Excerpts from the Anders circuit analysis ( my highlights  :

Acceleration Enrichment (AE) - Sheet 2 

The AE circuit provides immediate and delayed enrichment when the throttle is opened for acceleration. Throttle opening is signaled by the TPS through alternating ground signals from two inter-digitated traces that are each connected to the inputs of a flip-flop (see sheet 2 of the schematic for a drawing of the switch details). A drag switch in the TPS prevents these signals from being sent when the throttle is closing. The outputs of the flip-flop are sent to two edge detectors, whose outputs are combined and sent to pulse shaping and narrowing circuits. The pulse shaper provides immediate injection pulses to the IL (Injection Logic). The width of these pulses is independent of engine speed and load, and from Kerfoot's schematic, they are about 1.5 ms in duration. 

Idle Mixture Adjustment (IM) - Sheet 3

The IM sets the mixture (adjustable with IA) during idle operation. The output of the IM is combined with the output of the SC to control the voltage threshold in the PL for turn-off of T201. When the throttle is open, the IM appears as an open circuit and the SC controls the PL threshold. Note that the IM is effective ONLY when the IS on the TPS is closed!! Adjustment of the IA has no effect on mixture when the throttle is open.


EFAW 228 (Bosch p/n 0 681 500 001) D-Jet tester

  • Throttle valve switch I and II (accelerator circuit, 10 alternating contacts while opening throttle, 0 ohms on closing of throttle)
  • Throttle valve switch III (idle switch, 0 ohms when throttle is closed, infinity when opened more than 2 degrees)

    Throttle valve switch full-load contact (only for VW T3's from 1972)

    EFI Associates Model 9100 MPC System Analyze

    Car not running

    d: TPS Idle switch, full-load switch (if present), and immediate accelerator track switches (3-way switch to accommodate all TPS types)


    Adjustment procedure for TPS:


    Numbers from Ebay, Dutch seller:  peuver 

    Early Type:  PCB Type-17 for Bosch:  0 280 120 018  /  0 280 120 021 / 0 280 120 039 this is probably an error...039 is for the late version.

    Later Type:  Type-03  for Bosch: 0 280 120 007 /0 280 120 011 /  0 280 120 012 / 0 280 120 026


    Questions for Anders:  

    What is difference between 9,20,14,17 connector on Volvo and 9,20,12/47,17,2/14 of VW and -,17,12,-,9 of Porsche when PCB is identical?   Answered:  2/14 is WOT output Terminal, not used in Volvo application. 5 Terminal TPS (PN 028 120 047) can be used in Volvo application if 4 Term connector of vehicle is placed not to connect to 2/14 Term of switch.  Ref:  Rolling VCOA Magazine Jul-Aug 2016, Solutions for a faulty Throttle Position Switch by Bill Arey 

    TPS adjustment procedure calls for Throttle to be fully closed, but it would seem that Idle switch closes any time shafts turns CW.  Answered:  This is not the case due to TPS PCB layout, and interaction of Wiper Contacts!  See detailed dwg of TPS internals. 

    Does he have drawing which shows the connections of WOT switch of VW versions?  Answered: Terminal 2/14 OF 5 Term TPS Info added to TPS detailed drawing.  How does WOT switch interface to early ECU, or does it not?



    During deceleration, above 1500 RPM, throttle switch cuts fuel supply off and below 900 RPM, fuel supply is turned on.


    E-mail to Anders:


    Mr. Anders;

    I have seen your excellent work on the D-Jetronic (for years now) and have to compliment you on your dedication and work, and efforts to present it on your site!

    I am involved with the Volvo clubs, and as you are undoubtedly aware, the D-Jet was used in several models from this manufacturer.  I am also an EE (with heavy hands-on factor as yourself) and am currently very interested in understanding the TPS and really getting to the root-cause of its' well known "cough at cruise" symptom.  I have some thoughts on this I would like to discuss with someone who I can really "talk turkey" with, and who knows the difference between a negative edge triggered Flip-Flop and a hole in the I took a chance and googled your name for Phoenix, and came up with a number which I left a message on this past Sunday...I don't know if you got the message, but out of the blue like that, I might not respond to a message from a non-Porsche guy either, but I ask again if you might be so kind to allocate a few minutes of your precious time to discuss the finer points of the TPS with me, a fellow vintage car guy and D-Jet friend, I would very much appreciate it...and you might just get something out of it yourself...with the Cough at cruise symptom being pervasive, I'm surprise at the lack of info and root-cause and corrective action info out there... 

    ...and just plain BAD information doesn't help...I had a real laugh when I ran across this:

    Having studied the switch at length (including the VW version with WOT contact), I actually don't think the comb contacts have much to do with the cough at cruise at all, because according to my initial inspection, the sliding contact which supplies the comb conductors with ground and thereby a Neg edge to trigger the Flop is smaller in OD than the insulated space between combs (comb-wear and conductor smearing notwithstanding)...and even IF an extra trigger occurred, the resulting mixture enriching is unlikely to cause a misfire...I believe it is instead the hysterisis (or lack thereof) of the drag-switch which causes the cough (I've seen "2degrees" shaft rotation) because of a momentary switching to Idle (which would result in a lean stumble).  I think this is rather the root-cause (not "arcing" or "comb-conductor wear"), but again, this is what I would dearly like to discuss in depth with you.  My goal is to generate the complete and definitive documentation on this issue, including tests, adjustment and maintenance recommendations.  I think ALL D-Jet users, Volvo, Porsche, and VW alike could greatly benefit from such a documentation, and you are clearly the expert I would like to talk to...       
    Greets from Connecticut and Regards,


    Working Diagram tying all TPS info together

    My detailed consideration of the function of TPS in support of an explanation of the "cough at steady speed/throttle" also referred to as a MaC symptom: 

    1.  Diameter of the slider contact which sweeps comb conductors is smaller than the spacing between comb conductive teeth...this means that slider can never make contact across the two combs, or even that it makes contact with either comb at any one time.  Sliding contact can actually be between the two combs also, not making contact with either!  This is also consistent with the negative edge triggered Flip-Flop inputs the two combs are connected to at the ECU, where the two inputs would be triggered alternately in operation (Note 1).  Therefore, three contact conditions can exist:  Contact with one comb (term 9), OR contact with the other comb(term 20), OR between the two, and not making contact with either comb(open).  Resulting circuit function:  Flip-Flop T904,T905 remains un-triggered, and in a stable condition, holding last state. 

    Note 1.  As the Flip-Flop is an edge triggered circuit, it changes state at the first valid comb contact input, locking out ANY subsequent contacts (and in this manner exhibits high immunity to repeated or false triggers) , also, the only time Flip-Flop changes state is during CCW (throttle opening) rotation because Comb Selector Contact of Drag Switch is only closed during CCW rotation!  In this way TPS is direction sensitive.   

    2.  Drag Switch (internal to TPS), provides ground connection to Comb Slider when shaft is turned CCW (only). 

    3.  Idle Switch (grounds terminal 17, when Throttle shaft is closed turned CW). 

    Note 2.  Since Dragswitch powering comb slider is in essentially a SPDT configuration with Idle Switch, providing ground to either is exclusive of the other.  In other words, only one of the two circuits is enabled, at any time, as a function of Throttle Shaft direction.  Also there is a deadzone or Hysterisis between the connection of the two directions. When a direction change occurs, the contacts of the SPDT do not change instantaneously, because in the first place it is not a snap-action mechanism, and secondly the shaft moving them is turning slowly. 

    I therefore hypothesize that it is not the wearing of the PC board in the comb area which is responsible for the "cough" symptom, but normal ECU action in the deadzone during a (slow) switchover which is responsible.  It might be as simple as the idle contact being engaged at cruise through failed mechanical hysterisis (cutting off fuel) then the idle contact opened again (Update:  This is not possible!), the engine reaction might be a momentary lean stumble.   My research will concentrate on trying to substantiating this, as well as supporting the use of Deoxit D5 as a lubricant and preserver of the internal contacts. 


    The Edge Triggered Flip-Flop in the Enrichment Circuit.  Using this circuit configuration is brilliant engineering by Bosch, and why it is therefore not possible for the comb contact to be causing the "Miss at Cruise"  issue! 

    Bosch was indeed clever in their system design!...their use of an Edge Triggered Flip Flop (T904,T905 of the Kerfoot drawings) has complete and total immunity to false triggers from the Comb Contact!  Looking at the Comb Contact specifically, and the fact that each side triggers one input of an edge triggered Flip-Flop, it is clear that a worn, and intermittent (or a bouncing multiple contact), CANNOT be the cause false inputs ...the author can say this with a high degree, no...absolute(!) certainty, because of the nature of an edge triggered Flop.   

    Since it has the ability to latch, it’s also used as a bounce eliminator or in circuits where electromechanical switches are used as inputs to logic circuits. If the contacts bounce when the switch is closed, the logic device will only see the first contact closure. - See more at:
    Since it has the ability to latch, it’s also used as a bounce eliminator or in circuits where electromechanical switches are used as inputs to logic circuits. If the contacts bounce when the switch is closed, the logic device will only see the first contact closure. - See more at:
    Since it has the ability to latch, it’s also used as a bounce eliminator or in circuits where electromechanical switches are used as inputs to logic circuits. If the contacts bounce when the switch is closed, the logic device will only see the first contact closure. - See more at:
    Since it has the ability to latch, it’s also used as a bounce eliminator or in circuits where electromechanical switches are used as inputs to logic circuits. If the contacts bounce when the switch is closed, the logic device will only see the first contact closure - See more at:

    A Flip-Flop, also called a Latch, is a circuit configuration often used in control circuits as a bounce eliminator where electromechanical switches are used as inputs.

    When electro-mechanical contacts are closed, they typically bounce microscopically, giving multiple inputs to the circuit, which, if fast enough to respond to these (electronics certainly are!), can cause errors, if not allowed for, and accommodated...and the Flip-Flop does this perfectly!  By using this circuit configuration at the input, the downstream control circuit will see only the first contact closure, ignoring any and all subsequent closures, contact bounces or intermittents caused by PCB wear, because these are effectively "locked-out" and ignored, thus control errors are prevented. 

    Generic Flip-Flop circuit

    Detail of Flip-Flop Operation as it applies to the TPS:  Notice on circuit of Flip-Flop, because of the cross-coupling of the two transistors, once the FF has changed state as a result of the first valid low going edge to occur, presume closing switch at A (caused for instance in the Bosch D-Jet, by the first continuous connection through Comb Slider Contact, Comb Contact, Continuous Slider, and finally Continuous Pressure Contact), it doesn't care (or react therefore totally insensitive and immune to!) additional triggers on the same input...because as soon as this first trigger causes QA to turn off and to assume that stable state (and results in one single enrichment pulse due to the function of the downstream circuit in the ECU), it effectively locks out that input and renders any and all further negative edges on it as ignored (called a "Don't Care" operating condition).  [Once the door is closed, it cannot be closed again!]

    Therefore, the only, and next trigger which can result in a Flop state change must occur on the other Flop input (B, since even if it were to occur again at A, it would not be valid due to the ignored input condition)...and to get a valid input to the B Flop input would take a large physical shaft rotation to the next and alternate comb connection, compared to the small wear area that the moving contact is in at the time.  Again...a brilliant design with superior tolerance to wear!  Once the next valid triggering Edge comes at the B input, the FF changes to the other stable state, and this results in the next enrichment pulse due to the function of subsequent parts of the circuit...and so on and so forth up the 20 possible edges of the Comb Contact area.  

    Link to further Flip-Flip information on a popular reference site:

    Interesting to note is that the Distributor Contacts of the Bosch D-Jet, Trigger connect to an identical edge triggered Flip-Flop (T251,T252) as the Enrichment Flip-Flop, so this ECU input is therefore equally robust in its immunity to false triggers.  This circuit understandably has no provision for a Reset as Distributor contacts are constantly pulsing when engine is running...they do not have a resting or Idle or Reset position.   

    Extract from the Kerfoot ECU Wiring Diagram Sheet 1, showing a Flip-Flop input circuit for the Distributor Contacts. 



    Link to FI troubleshooting manual:


    Links and Troubleshooting Thread Excerpts [Yellows are addition Comments/Corrections which were not part of the original posting]:

    [From]... in response to:   "'73 p1800 es throttle position switch 1800" posted by posted by  "flaps" on  Wed Feb 25 18:18 UTC 2004


    On the earlier TPSs, the plastic cap just snapped on, and just as easily snaps off to reveal the innards...and IF you have on of those, go ahead and remove it from the throttle housing (make witness marks to help getting it back in the same place on reassembly), then carefully pop the top off, blast clean with spray solvent, and inspect:

    1. PC board foils (especially the area where the slider sits almost forever at cruise throttle openings) if edges of conductors show excessive wear at the edeges, that's the classic cause of hiccups at cruise. If worn away, there's not much to repair for even the most ambitious Brickboarder...replacement is about the only option...that's why I've considered making an optical (ZERO contact) replacement for those damned switches... (cost?...but it's got to be better than those damned things... who's interested? If it doesn't look too bad, lubricate liberally with Deoxid D5 *, pop cap back on and reassemble, using witness marks as a guide (lubing the shaft couldn't hurt).

    * see also:

    2. Mechanical switch contacts of idle sensing switch.

    I have no experience with late, replacement TPS, which I understand it is not possible to open (maintenance free?...BS!...more like unmaintainable!...just like the car batteries)...somebody needs to be slapped for that!).


    [From]... posted by John Mc on  Fri Nov 28 20:30 UTC 2003 [used with permission, because I couldn't have explained it better myself!].  Link to Thread throttle 1800 [E]:

    PS - those contacts in the throttle switch. The computer doesn't really need to know the actual position of the throttle - it gets all the info it needs to know about the air going into the engine through the air temp sensor and the manifold air pressure sensor. That switch does two functions.

    1) Idle circuit: To squeek by early emissions laws the computers had a special idle circuit which was individually tuned on the line with an adjuster on the box. This fine tune adjustment is ignored when the throttle is anywhere but closed. So there are a couple of contacts in the switch to indicate this.

    2) 'Accelerator pump': When you suddenly open the throttle on any car the engine needs just a bit of extra gas or it will stumble slightly. To do this they have the throttle switch send some pulses to the computer - which just adds an extra injector firings for each pulse (typically injectors are fired only when the trigger contacts in the base of the distributor pulse). There are two independent injector circuits (they fire in pairs) and if you look in the switch a single contact slides up between a sort of interlocking zipper sort pattern of contacts, so as the contact slides up it first hits one side, then the other. Of course you only want this to happen when the throttle is opening, so that portion of the switch is sort of friction loaded, and when the throttle opens it rotates slightly on the shaft and closes a couple of contacts to complete the circuit, when closing those contacts are pulled open so you don't get the extra injector fires as the throttle closes. This 'electronic accelerator pump' action works even if the engine isn't running, turn the key on and if you listen very carefully you should hear the injectors clicking as you open the throttle, not when you close it. If it isn't working the engine will run just about as well as with it working, in fact you can totally unplug the throttle switch plug and barely tell the difference. I think the engine is a little slower to respond to quick throttle openings, but it's not something you'd particularly notice unless you were looking for it.


    Good day everyone,
    I hope someone can assist here. My 71 1800 has been having a problem. She has the original engine B20E. What is going on is, there is a HARD hesitation while driving at a steady speed/rpm. We have not been able to recreate in the shop. Seems it is only while under load (driving). It feels like a flapper or whatever in the air intake is closing off all airflow for a split second. The hole car then "bucks" hard. Has any one had this condition, and knows what to do? She runs good, and is at 248K miles. P.S. The condition goes away with a slight increase or decrease in RPMs. Only happens at steady rpm under load. We have replaced the Throttle Control Switch with a new unit. I have preformed the adjust check. I count 15 clicks than a large gap (around half to 3/4 throttle) then almost full open, I get a few more clicks. This gap makes me think it would be in the area of 50-65 mph on the road, and that's the area where the bucking is hardest. Am I doing doing something wrong in the adjustment of the switch? Could it be elsewhere? This was slightly happening before I added items like the fireball elec ignition, and replaced the injectors. So I don't think that's it, but on these system, I just don't know. I was even thinking timing chain slop?

    Help please.



    turn the car [Ignition] on, don't start. as you SLOWLY move the linkage, the injectors should click once every time a new spot on the TPS is found. there are supposed to be 20 separate spots, but 17 or 18 will do. if you don't get a click, move the engine slightly, the trigger points may not be open. good luck, chuck.


    [From]... in response to a long thread of 1800ES with No-Start:  

    [First, an attitude-check...]...very good info and recommendations already in this in thread, particularly from Eric and 142G! Also, there is much info out there on the D-Jet Inj Sys (the granddaddy of all modern FI Sys!) with which you should familiarize yourself with (unless you want to send the car to a specialist like Eric and put down your money...your choice!) previously mentioned, and don't take this wrong, but if you don't take the time to become at least very familiar with this system, and expect us to spoonfeed every bit of info which you SHOULD have going in, then get frustrated when sorting this out takes time (sorry, likely no instant gratification to be had here!), I question if we can help someone with such an attitude...we don't expect you to become an expert, but you must understand function of D-Jet Sensors and Actuators in order to troubleshoot! ...that said, suggested reading: My notes:

    I'd like to add some things and reiterate some others for emphasis...

    [...then, down to technical business...!]...when Ign is ON, Supply pressure in Fuel Rail to Injectors, supplied by Fuel Pump and regulated by Fuel Pres Reg, MUST be 28PSI ...that constant, and the (unchanging) orifice size of Injectors is what the entire D-Jet is based on...Injector energization (opening) time is only variable which ECU controls to vary injection amount...dump FPR must have a clear return line to function as intended, and you already have learned about the 3V energization voltage of Injectors...! Also, a VERY common issue on these cars is a fuel feed restriction due to rust particles from the Tank clogging filters (I fought with this for a while on my '73 ES, as it can lead to strange symptoms!), but unless fuel restriction is complete, this is not a cause of a No-Start...(just watch for it as it is quite common!)

    Fuelrail pressure will tend to leakdown after shut-down...that's to be expected with non-new equipment!...only if this is virtually instantaneous is this an indication of a possible leak (or bypass), but if leakdown takes more than 30Sec, it's not a crisis, and certainly not the cause of a No-Start! Presuming elec and plumbing connections to Temp and Manif Sensors, and ECU (of course) are intact, you must have enrichment by Cold Start Valve to enable starting (note that '73 ES had the later, ECU INdependent, Thermo Time Switch controlling CSI. Here, the ECU is NOT in charge of enrichment! See: )...and I must accept you stating that Ign Sys is working and timed correctly...

    Have you pulled Spark Plugs after No-Start...are they wet or dry?

    Absolutely correct info on Dielectric grease by 142g (Kudos, and thanks for getting it right and spreading the word!) Electrical connections of sensors and everything having to do with the D-Jet (and the rest of Elec Sys for that matter!) should be Clean (meaning shiny metal!) and tight (whether push-on or bolted connection!). Loose the Dielectric grease(!) and apply Anti-Corrosive Zinc Paste on all connections (except Hi-V ign) AFTER cleanup and during reassembly/reconnection. See: The only place I don't recommend it for is the Throttle Posit Sensor. See:

    Eric; Caution! (I respect your input and experience greatly, but must raise an objection here): ...the high pressure fuel-line which is supposed to be used with the D-Jet system has internal reinforcement which if crushed (even if only temporarily, to stop fuel flow for test purposes) will damage it!...I recommend against this...yes, it is a pain to disconnect and plug fuel lines (and GREAT care must be taken, and Fire Precautions exercised, with the possible squirt of fuel from a line which is holding those 28PSI. BEWARE ROB!!!), but internally damaged Fuel Line is not a good thing as they can leak without warning!...then there is a fuel leak fed by high pressure...that's double badness!

    Eric and 142g; I've heard that the source of raw fuel getting into crankcase can be a leaking CSI...have you heard of any other sources? sounds like this should be one of the first things to concentrate on...if not, scored cyl walls due to lack of lube will surely increase the scope of the project...

    That's it for now Rob...please keep us informed of your progress and findings, and we'll try to keep you from getting distracted by non-critical things, and pointed in the right direction!

    Good Hunting


    Another 1800ES No-Start:  Link to Faceplant thread:

    My response to symptoms of "Feels like engine is willing to start but as soon as starter is released it will stall."

    ""willing to start but as soon as starter is released it will stall." ...typical symptom of fuel delivery by ONLY the Cold Start Injector...once Starter is disengaged no fuel is coming from cylinder Injectors...these are either not being powered with injection pulses (listen for these!) OR bound up with fuel gum (also not uncommon!)...[Comment:  Pintle orifice on CSI is also much bigger than normal cylinder Injectors, because of much higher fuel delivery rate(!) so it it less susceptible to binding up due to fuel gum.] to check, remove Fuel Rail and check for fuel and spray pattern (into a catch container) from Injector. OBSERVE SAFE OPEN FUEL AND FIRE PREVENTION PRACTICES!! See also: Work Safely and Good Hunting!" 


    Excerpt of my answer to a poster (CD) who got a non-running 1800ES, and was asking about how to proceed

    "...First of all, without declaring to whom you sent your ECU and who declared it "bad and unrepairable.", and without giving further DETAILED INFO, I must highly question this finding! Based on what recommendation did you send it where, and what are their qualifications for working on D-Jet ECUs?? (It is crucially important only to deal with known qualified and recommended expert on the half century old, completely analog D-Jet at this point! So-called "FI experts" whose first question is where to plug in the OBDII port NEED NOT APPLY!)

    As BH, stated [ permission to publish name, so initials only, but you know who you are!], D-Jet ECUs are HIGHLY reliable and typically the LAST thing which comes under suspicion! If the car came to you non-running, that doesn't make it any simpler for an inexperienced new owner, but all is not lost! The VERY FIRST thing I would recommend is that you reassemble everything to a known factory unmolested state based on the Service Manual...and some preventative electrical maintenance to assure good connections all around couldn't hurt at this point!  [This includes power by way of FUEL INJECTION POWER RELAY, and also FUEL PUMP RELAY, and Fuse 5 supplying this relay, and also common chassis return connection at rear of Intake Manifold.]  Harnesses can get brittle from heat and age, but that can be found by visual inspection and repaired...important is to check FI connectors for damage and good connector function...FI Trigger Contacts in Distributor can be removed cleaned and checked...GENTLY! ...Manifold Pressure Sensor MUST be able to pass the vacuum leak-down test, before engine can be expected to run properly and reliably, see:

    Then, you need to check there is fuel pressure in the Fuelrail of the system on Ign ON...this verifies ECU is getting powered, is controlling Fuel Pump, which is in turn charging Fuel Rail. After that, function of Injectors can be checked, and this can be simply done as a function of TPS. See:

    The D-Jet is a simple FI control system [which does, when everything is in nominal condition, work very well!], but it does require connections to Sensors and Actuators to be clean and in good electrical condition.

    Tell us how you make out, and always give as complete a starting condition, and symptoms description as possible. See if you can locate an experienced D-Jet owner in your area who might be persuaded to stop by... Good Hunting!


    An easy one...seen on "Jeopardy" 8 Oct 2021!



    Fact-checking wikipedia!  

    I realize that wiki contents can be posted anonymously by anyone, so with such a high potential for incorrect and factually creative contents, it should always be double-checked against other reliable sources...and that is surely needed in the description of the Bosch D-Jetronic! 

    I on the other hand, stand behind what I post on the SW-EM site and fora with my name, so when I see "info" as the excerpt below, the reader will allow me some comments, (which are my own, and I also stand behind!)

    My comments to Dave F. after he forwarded the above wiki extract:  

    "Electrojector System" ...what's an Electrojector System?  ...first time I've heard that term applied to Bosch D-Jet...(re)search shows it is apparently a super-groovy term the Marketing Department of Bendix came up with when they developed their first injection systems...I've never heard it applied to the Bosch System before, hope never to EVER hear it applied to it again, and hope it dies a peaceful death in the annals of automotive history books...

    "ultimate failure" not how I would describe a system, thousands of examples of which still work just dandy a half century later, and whose descendents and license built copies and further developments power just about all cars of today!  Sure it has been surpassed by ever developing and evolving technology, just like your Sony Walkman, but was (superbly) well designed and executed, and performing(!) given the technology and state of the art of the day!  Reminder:  True Quality always stands the test of time!

    ...what "paper-wrapped capacitors"? this wiki writer suggesting C500 and 501 or any other Caps in the ECU are paper wrapped Caps?  I believe the writer is once again under/uninformed!!...because all other caps I see are superior quality caps, again, NO different from the components we specified and built, and CONTINUE TO BUILD, into high reliability military avionics...a branch I have some familiarity with! ...and btw, any deterioration of C500, 501 (decrease in C) which look to me like they are strictly in a switch snubber function on the Injector control transistors, would only result in working those transistors harder (perhaps causing them to run a bit warmer) than when these caps were at their starting value (certainly not causing an FI failure).  These caps are located WELL behind the critical sensor processing circuits of the system, and would likely not affect the accuracy of the injection function.  

    "amplitude modulate (AM radio) signals to control the injectors" ...WHAT???  ...what creative wiki contributor came up with this twaddle???  Processing of sensor inputs is by means of (superbly) designed (and constructed) linear electronics, (state of the art of the day, and incidentally state of technology which also got us to the moon and back, so it can't be too terrible!!) and final control of the injectors is strictly digitally ON or OFF, and absolutely no different than how they are controlled in 2023 by the latest and most advanced Bosch Motronic btw!  Calling precision linear signal processing "lack of processing power" suggests this was again written by a completely under-informed youngster who believes that if the D-Jet ECU doesn't have an Intel or Motorola micro-processor crunching millions of lines of code at light speed, "it simply can't be expected to be able to process the necessary inputs"...THIS IS ABSOLUTELY WRONG!!...again I refer the writer back to linear processing which was successfully employed for all sorts of precision control loooong before digital processors ever came along...

    I presume with "the unavailability of solid-state sensors" the writer is referring to the Manifold Pressure Sensor, with its diaphragm cells and bellows (with a long but limited service-life expectancy) because the Temperature Sensors of the D-Jet certainly ARE most certainly solid state!

    "unsuited for heat-cycling"...this statement and assertion is out and out more unsubstantiated hogwash!! far as I'm concerned, as the D-Jet ECUs were burned-in at the factory as a reliability assurance step, shows that they WERE in-fact "suited for heat-cycling", and this is no different from the highest quality/reliability avionics, produced at the time, (and continues to be a part of reliability assurance to this day!), and you Dave and I know something of this area...!  I'm quite certain (and physical inspection and track record absolutely proves!) that Bosch did not design their ECUs with inappropriate or inadequately rated components in the first place(!), in the second place, ECUs were in-fact NOT located in the "heat-cycling" engine compartment, but in the relatively cozy passenger compartment, so as an engineer very familiar with reliability burn-in of control systems, I expect the worst case thermal cycling they EVER saw was during production burn-in at the factory, and not in service!   

    Rant complete!  That wikipedia entry needs a SERIOUS update and rewrite!!


    Sources of external materials are attributed.  Otherwise, this page is Copyright © 2015-2024,  Ronald Kwas.  The terms Volvo, Porsche (a family name, and A TWO SYLLABLE WORD!) and Bosch are used for reference only.  I have no affiliation with any of these companies, other than to try to keep their products working for me and reliably, and to help other owners do the same.  The results and highly opinionated thoughts presented here are from my own experience, and should be used in conjunction with normal, careful shop practice (ESPECIALLY THE PART WITH FLAMMABLE GASOLINE IN THE OPEN!), or can be ridiculed and laughed at, or worshipped, at your discretion.  Remember, you alone are in control of your future, and your knuckles! 

    As always, if you can supply related additional objective info or experience, I’d appreciate hearing it, and will consider working it, along with the odd wise*** comment, into the next revision of this article.  You are welcome to use the information presented here in good health, and for your own noncommercial purposes, but if you reprint or otherwise republish it, you must give credit to the author or link back to the SwEm site as the source.  If you don’t, you’re just a lazy, scum sucking plagiarist...and the Boston Globe wants you! 


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