Bosch D-Jetronic Fuel Injection Notes Compilation
10/2015 R. Kwas  changes/additions ongoing
Most recent updates and changes:  Jul 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!  See also:  CAUTION AND VERY IMPORTANT SAFETY TIP !

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

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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?" ...it 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:   http://members.rennlist.com/pbanders/ecu.htm  ...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, https://jetronic.org/en/D-jetronic ) 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

PLACEHOLDER FOR MORE ON DISTRIB CONTACT ASSY. 

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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:  http://members.rennlist.com/pbanders/ecu.htm#D1-D2  

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:  https://members.rennlist.com/pbanders/ecu.htm#IL ]

My posting to thread:  https://www.brickboard.com/RWD/volvo/1667230/1800/p1800_es.html 
“....Injectors are NOT designed or intended for a full 12V...in 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!...no 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 longer...like a week!]...best practice is to NEVER apply a full 12V or continuous power...it'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):  https://learn.sparkfun.com/tutorials/measuring-internal-resistance-of-batteries/internal-resistance

Placeholder for Notes on Snubber Circuits: 

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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:  http://www.sw-em.com/D-Jet_Manifold_Pressure_Sensor.htm 

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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(!)...an 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 for...it 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:  http://www.sw-em.com/Deoxit_D5_Additional.htm#TPS_Maintenance 

TPS Conjecture:

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

https://www.swedespeed.com/threads/my-volvo-throttle-position-sensor-woes.640202/#post-7983654

"There is no bridging which occurs between the Comb Contacts...it 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! "

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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

From:  https://vcoa.org/index.php/forum/9-P1800-1800S-1800EES/98-setting-idle-on-a-b20f-d-jetronic-fi-system?start=0

Idle Adjustment Screw and Locking Nut in Throttle Body. 

Fuel Pump Control:

FuPu control is by way of a timer circuit, which is powered whenever ECU is powered up, but will "time-out" after approximately 1 second or so dropping the external Fuel Pump Relay, if it does not receive pulses from the Basic Injector Pulse processing circuit (which in turn gets triggers from the Distributor Contacts located on Sheet 1.). 

This results in the audible operation of the FuPu and then, if the Starter is not engaged, the pump also stopping after about 1 second.  Some refer to this as "priming" the Fuel Rail, but 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, this action is absolutely normal and intended by design. 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.   

Refer to:  Marked up Wiring Diagram for D-Jet Troubleshooting  It should be noted that the FuPuRelay is powered by the Main Fuel Injection Relay, but this does not in-turn power the FuPu directly!  Actual FuPu power is by way of the separate Fuse5, so when troubleshooting a No-Start condition, simply hearing the FuPuRel click and not hearing the FuPu running, the next step should be having a look at Fuse5.  It is not unknown for the conical ends of the fuse to be contaminated and develop a poor connection disabling the FuPu.  All Euro-fuses and their associated Fuseblock contact should be cleaned and reinstalled with ACZP to prevent this nuisance failure.  See:  ACZP 

See also:  http://www.sw-em.com/Fuel_Delivery_Components_and_Considerations.htm#Electrical_Fuel_Pumps

PLACEHOLDER FOR additional material.

Cylinder/Coolant Temperature Sensor:

From Dr-Djet's page:  https://jetronic.org/index.php/en/d-jetronic/72-troubleshooting

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.

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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)

PLACEHOLDER FOR INCREDIBLY INSIGHTFUL INFO AND GROOVY COMMENTS ON SHEET 3 CIRCUITS!

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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:  https://www.sw-em.com/1800E%20Wiring%20Diagram.jpg

'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:  https://www.sw-em.com/1800ES%20Wiring%20Diagram.jpg

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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:   http://www.turbobricks.com/forums/showthread.php?t=335193 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 ( https://www.swedespeed.com/threads/unknown-ports-b20f.680791/?post_id=8241611#post-8241611  ).  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):  https://www.v1800.org/index.php/en/bosch-dj-en/dj-units-en/dj-cold-start-en/dj-thermal-time-en.html

Thermo-Time Switch (TTS) in Situ. 

PLACEHOLDER FOR Cold Start Injector/Valve material.

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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.  

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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

PLACEHOLDER

Copy of my comments to a Brickboard thread:  https://www.brickboard.com/RWD/volvo/1678715/140-160/1971_142e_will_run_life_140_start.html 

"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):  https://www.brickboard.com/RWD/volvo/1669422/1800/fuel_pump_questions.html

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

Copy of my clarification to thread:  1972 pv1800es [Although there is no such vehicle!] https://www.volvoforums.org.uk/showthread.php?p=2741164#post2741164

(FuPu Time-Out)  FuPu is under control of the D-Jet ECU, by way of (ECU Pin 19) and FuPuRel...but to answer the question...it 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:  http://www.sw-em.com/Fuel_Delivery_Components_and_Considerations.htm#Electrical_Fuel_Pumps

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

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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 engine...no problemo! See: https://www.sw-em.com/Product%20Reviews.htm#Tri_Flow 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 there...as 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..."

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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 gauge...it 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!  See also:  Fuel Safety Caution from Jay Leno!

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 ).  

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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 starvation...as I posted in the linked VOC Forum [https://www.volvoforums.org.uk/showthread.php?t=46969 ], 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 away...best to be done with a near-empty Tank (less fuel to deal with)!

See also: https://www.sw-em.com/Fuel_Tank_Notes.htm#1800ES_Tank 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 GCP.se 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 

PLACEHOLDER FOR MODEL AND PN INFO

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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! 
 Observe fire prevention practices! ]

Chris writes in this thread:  https://www.brickboard.com/RWD/volvo/1678760/140-160/1971_142e_will_run_life_check_fuel_delivery_140_start.html  ):  "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:  https://www.swedespeed.com/threads/fuel-injector-spray-test-questions.662193/page-2

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...).

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Injector Cleaning:  

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

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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 tubing...so 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 FuPu...it 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!"

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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:  https://www.facebook.com/100002260028678/videos/1211992159646481/

(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."

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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 on-line...in 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 department...here 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!

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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:  https://www.sw-em.com/electical_circuit_interaction.htm   ) 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.  ...so 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:  https://www.sw-em.com/feedback_and_testimonials.htm#Swemming  ), 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!  ...it 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! 

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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

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Link to very good troubleshooting guide:  http://volvo1800pictures.com/document/fuel_injection_fault_tracer/fuel_injection_fault_tracing.pdf

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. 

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Phil Singher's excellent general write-up on Bosch D-Jet:  http://www.vclassics.com/archive/efi.htm?fbclid=IwAR3GvofBXLjkH_QFc1_SFo6E6fxqALmxz02Wt0_7fMlv_GEbe0ABGCV8CHA 

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Part Numbers:  Source?

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Throttle Position Switch (TPS) Additional: 

Source:  http://members.rennlist.com/pbanders/Scholl_2.pdf

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

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More Links at the Volvoniacs on the TPS:  http://www.networksvolvoniacs.org/index.php/Spezial:AWCforum/st/id1928/limit:0,15/#last

D-Jetronic DKS Drosseklappenschalter:  http://www.networksvolvoniacs.org/index.php/Spezial:AWCforum/st/id4878/drosselklappenschalter.html

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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 repro-parts.de

Nachproduzierte Platine Drosselklappenschalter . bei office bei v 1800.org

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Source:   http://members.rennlist.com/pbanders/djetparts.htm

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Replacement PCBs for TPS from:  http://www.914world.com/bbs2/index.php?act=Attach&type=post&id=453057 
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:  http://members.rennlist.com/pbanders/TPS%20Contacts%2003.jpg

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.

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Link to D. Farrington pictures:  https://drive.google.com/folderview?id=0BwOnJ74Oi_8xY2dKV1FVYnBBMXc&usp=sharing

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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!         

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TPS related Excerpts from the Anders circuit analysis ( http://members.rennlist.com/pbanders/ecu.htm )  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.

From

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