Remedy for a hyper-sensitive Tach on an 1800ES: Two Ignition capacitors (short: Caps) added near and to Ign Coil+ (15). "The double capacitor fix worked great until the sale and I've not heard about any troubles from new owner". Craig K.
Electronic Upsets on Powerbuss cause Functional Dropouts on D-Jet Equipped Cars!
Apr 2024 R. Kwas [Comments Added]
[I did not intend for this investigation to become a major engineering project, but the further I went down the "understanding the root cause rabbit-hole", the more it became apparent that multiple things were happening and needed to be considered...so in the interest of thoroughness, the investigation and presentation of the multi-part solution, has taken on a bit of a life of its own...]
This Tech article is published without reference and supporting material in the July-August edition of Rolling Magazine, and I will continue updating the on-line version as more info develops.
--------------------------------
In working with owners to troubleshoot, locate and address unusual functional symptoms on their D-Jet equipped cars, I have noticed the trend which suggests that in three of these cases, the root cause is related to electrical buss upsets, and that functional issues are at least in-part, caused by decreased immunity to electrical noise and powerbuss upsets...
...so until a root-cause is fully understood, the roundabout explanation is that on these vehicles exhibiting certain functional issues, the original filtering of electrical noise is no longer sufficient or effective in keeping noise or power upsets from affecting the normal function of some sensitive systems. Either the electrical noise or upsets have gotten bigger (unlikely, since the components generating them have not changed), OR the immunity to powerbuss upsets has gotten less (more likely, since there is a well known age related phenomenon at work, and we will explore this)...or both!
What are these "Sensitive Systems"? In two cases the D-Jet injection Sys was affected, in another, the Tachometer was. The Tach is obviously not critical to the operation of these cars, but it does contain sensitive electronics in order to detect and display RPMs by monitoring primary circuit Ignition System pulses. The Tach can also act as an indicator of electronic noise issues, so for the purpose of this consideration, falls under the definition of "Sensitive System".
Before undertaking a detailed root cause analysis, these "issues" could be categorized as age-related, (the suspected cause being: dried electrolytic capacitors) because they all exhibit the symptoms of being triggered by electrical noise, and they were all cured by decreasing the generation of this noise at the source, and adding new (and electrically effective) filtering to the Ignition powerbuss.
Maybe what these owners are experiencing on their cars is that they are coming out of the bottom of the Reliability Bathtub Curve...this term is not a joke!
Occurrence 1:
1800ES "Hyper-sensitive" Tachometer.
Occurrence 2:
1800E Reverse Relay affects D-Jet
Occurrence 3:
1800ES Horn Relay affects D-Jet
Solutions and Mitigations
Parts 1 & 2
Solution Part 1
Implementation of Solution
Part 1
Solution Part 2
Solution
Part 2a
Solution Part 2b
Solution Part 2c
Wiring Diagram Excerpt with
Solutions Part 1&2 added
Overall Conclusions and Summary
Making an Appropriate Kit Available
Reference Information:
General Maintenance
Dried Electrolytic
Capacitors
Notes on Suppression
of Inductive Spike
Inexpensive
Handheld Oscilloscope
Free-Wheeling
Diodes and Relays
Volvo Service Bulletin - Functional Disturbances
Acknowledgment of
Susceptibility to Power Buss/EMI Disturbances
Examples of
Bosch Relays with Internal Suppression Diodes
Clamping Diode Polarity
Paralleling Terminals
Ceramic Capacitor Technology
Reliability Bathtub Curve
Volvo and ElectroMagnetic Testing
-------------------
Occurrence 1: 1800ES. Adding Ignition Style Capacitors at Ign Coil + terminal (15) cures a "Hyper-sensitive" Tachometer.
Links:
https://www.sw-em.com/Smith's%20Tachometer.htm#Age_Related_Problems
https://www.sw-em.com/electical_circuit_interaction.htm#Headlight-Tachometer_Interaction_on_1800ES_Solved!
Symptoms and Explanation of Conditions: Tach exhibited hyper-sensitivity (bouncy Needle!) when activating Headlights Hi/Lo Beam Control. [or was it really DEactivating? This is a big hint!] This is consistent with increased sensitivity to ignition pulses being registered on the Tachometer, as its sensitivity to electrical noise has increase due to its internal filtering being no longer adequate (Suspected Cause: dried electrolytic caps!), and the electrical spike upset of the Ign Pwr Buss resulted in an affect on the Tach circuit. Symptoms were cured by adding two Ignition style capacitors (formerly also known as: "Condensers") to the Ign Pwr Buss near the Ign Coil. Owner advises the car was subsequently sold (which he "regrets, starting the day he put the funds into the bank", instead of having the car!) but the new owner has not reported any new issues similar to those addressed by the noise mitigation solution.
Unfortunately, and in terms of this investigation, this means I cannot get further data or a long-term report from him (unless of course the new owner becomes known, or makes himself known, to me)!
Craig Keller picture shown with his kind permission.
Remedy for a hyper-sensitive Tach on an 1800ES: Two Ignition capacitors
(short: Caps) added near and to Ign
Coil+ (15). "The double capacitor fix worked great until the sale and I've not heard
about any troubles from new owner". Craig K.
Note: Ignition caps are typically in the 0.2 - 0.4uF in value. See Reference Information: Ignition and Other Capacitors
-------------------
Occurrence 2: 1800E DEactivating the Reverse Light Relay causes a stumble at idle.
See also: https://www.sw-em.com/Reverse_Gear_Affects_Ignition.htm
Symptoms and Explanation of Conditions: See also link. Troubleshooting of this issue is still in progress and not yet finally resolved [It's pretty much resolved at this point, see Update below!], but pulling the fuse which powers Reverse Light Relay, eliminated a notable stumble at Idle symptom, as it removed the stimulus causing it (electrical upset of the Ign Pwr Buss). Presumptive cause is the electrical upset at instant of relay current cessation, combined with a possible decreased immunity to upsets in the D-Jet ECU. The electrical upset has either increased (unlikely, since it is still being generated by the same relay!) or it is not able to be adequately filtered out by the internal filtering of the D-Jet ECU, because this has become less effective with age (much more likely!).
Owner has subsequently also confirmed the symptom of "When the engine is not running (ignition on) the fuel pump cycles when toggling in and [specifically] out of reverse." This is precisely the same symptom as was experienced in Occurrence 3, so I expect the same cause, and solution to address this!
Update to Occurrence 2 - 5 Mar: "The [suppression] diode works! No more power cycling of the the fuel pump when switching thru reverse and horn!" Elliot L.
-------------------
Occurrence 3: '73 1800ES DEactivating Horn Relay OR Hi/Lo Beam Relay causes Fuel Pump to cycle and time out.
This symptom was noted during prestart checkout of a newly rewired chassis...with a new (used) harness. [Owner hadn't even gotten to starting it yet for the first time after major work, but I expect if he had, the symptoms would clearly be similar to Occurrence 2! ...it sure sounds like both owners are really dealing with similar issues!]
Symptoms and Explanation of Conditions: Electrical upset of Ign Pwr Buss causes ECU power to be cycled, and Fuel Pump Relay is dutifully following control by the ECU (pin 19). Note: Fuel Pump is not the source of the problem, only the symptom!
Paul Denno material shown with his kind permission.
Paul actually found a radio
interference suppression capacitor already installed next to his Ign
Coil, (these are typically installed on the Generator or Alternator output when
an on-board Radio was installed).
Researching this Bosch PN shows it is a high capacitance (2.2uf), low voltage (100V *) type. This is good and a step in the right direction, but alone doesn't alone prevent symptoms, since the relay release spike is still present to some extent...
* "Low" Voltage in that it is not subjected to the extreme high voltage spikes occurring across the points in a points based ignition...the capacitor voltage capability for those applications must have V ratings of >6-800V to be able to endure the huge spike occurring when the contact opens, so it should be apparent that these suppression components are rated very differently because they are performing very different jobs. The typical C value for these is also about one tenth of the radio interference suppression Caps.
Close-up of the Suppressor Cap, showing ratings and Bosch PN:
Close-up from the picture above: 2.2uf 100VDC Bosch PN 0 290 800 007
(Noise Suppressor Capacitor).
[Update to Occurrence 3 - 13 Feb: [Adding free-wheeling diodes to Horn and Hi/Lo Beam Relays] "...entirely eliminated the symptom of the FPR cycling/being cycled by the ECU." Paul D. ]
This is certainly a good and expected result (removing the trigger of the symptom), but the symptom is merely a resultant, and not the root cause! It is questionable how long this will prevent the symptoms from returning, since these seem to be a result of continued diminishing immunity to the triggers. Will the sensitivity continue to increase...and symptoms return? As an engineer, who is always looking ahead to anticipate (and be ready for) the future...a reliable solution must therefore be two tiered...removing the trigger AND bringing the level of immunity to power upsets back to what it was originally...
General Conclusions, and process used to confirm the nature and trigger of the symptoms:
Since the moment of occurrence of the symptoms is concurrent with release of a inductive current, this gives the qualified and experienced electronic troubleshooter a huge hint! It is well-known, that turn-off spikes are generated when stopping current in inductive circuits...this is in fact the exact manner in which ignition system high voltages are generated, but these spikes of transient energy can also cause problems in sensitive circuits (even damage in some cases)!
We also know that there was no such thing as Coil Suppression components in place on Relays of the D-Jet equipped 1800E and ES models. Such a measure was probably cost prohibitive at the time, and not found to be technically necessary as the internal filtering of the ECU was adequate, effective, and the unit was not susceptible to malfunction as a result of the relay spikes. I my research, I did find that the factory did Acknowledge Susceptibility to Power Buss/EMI Disturbances with a Service Bulletin.
To verify the resulting spike was the cause of problems, a fast capture device was needed, and an inexpensive oscilloscope did the trick. Once set up with a negative triggered single sweep. the spike upset was seen in all its glory...
The "Toy 'scope" was also used to verify that mitigation efforts of Filtering and spike suppression were successful in calming the Ign Pwr Buss, and restoring normal uninterrupted operation. See also: Inexpensive Handheld Oscilloscope
Inexpensive oscilloscope captures and displays the demon powerbuss upset
(negative spike on left).
It is the author's considered position after extensive theoretical and practical research, and peer review, that a two step process must be used to address this issue and vulnerability. First, the Relay Turn-Off Spike will be mitigated...this is a relatively simple task as it is a well-known characteristic of inductive loads as the relays are, and proven mitigation techniques have long existed and are well understood. Diode clamps can be retrofit as Solution Part 1.
To see the extent to which the relay turnoff spike(s) upset the power going into the D-Jet ECU, the ECU power line was monitored. This is more difficult to understand because it is not simply quantifiable, but decreasing the sensitivity to upsets must be an important second part of a lasting solution...otherwise, if sensitivity to upsets returns as filtering continues to become less effective with time, the symptoms could easily return! A long-term solution cannot be limited only to Solution Part 1. Solution Part 2 must also be implemented to restore a level of immunity to electrical upsets!
Solutions and Mitigations Parts 1 & 2 (...sometimes also known as: Belt & Suspenders):
Solution Part 1. Coil Arc Suppression:
Free-Wheeling Diodes are a well known and common technique for quenching the turn-off spike which occurs in Relays or other inductive loads.
Relays are available nowadays with suppression diodes built-in at time of manufacture, but that does not mean D-Jet powered Volvo owners cannot benefit from them also (and that we actually need them and will benefit from them has been clearly established)! Thankfully, suppression diodes can simply be externally retrofitted to Relays and inductive loads, and that is Part 1 of the two-pronged solution presented here, since it has been shown in both cases, that this addresses the trigger of the functional issues.
Bosch actually designed in a Free-Wheeling Diode into the D-Jet ECU in one circuit location. See: Diode Snubber in D-Jet ECU
Adding an external Free-Wheeling Diode: The common solid state silicon diodes (1N4007) we will be using are packaged with axial solid leads, which makes them somewhat mechanically vulnerable and it means that when retrofitting them, special considerations must be observed to assure the diodes remain functional, and are not damaged due to being subjected to mechanical or other insult during installation or subsequently.
Retrofittable Suppression Diode:
An assembly is made up as seen below.
With a couple of strain-relieving bends and insulating sleeving, the entire assembly protected by a final PVC Oversleeve (with a drip-hole), it can be simply added to terminals 85 and 86 with paralleling crimps, and observing polarity at time of installation! Polarity is important! BLU to Neg (85), ORN to Pos (86)!
Retrofittable Snubber Diode Assembly with Paralleling crimps, final Oversleeve
removed. Horn and Headlight Relays, and Reverse Light Relay (present in
earlier models) need to have one installed,
[possibly even the Wiper Motor!] to
keep these relays from generating the upset, because these relays[/inductive
loads] might be activated any time during engine operation to result in
FI stumbles or worse. Fuel Injection Relays (located on inner fender aft
of Manifold Pressure Sensor,
see below: FI Associated Relays) can have a snubber
diode retrofitted optionally, because since these Relays are only activated at initial Ign ON,
and remain ON for the entire running session, so they are not in a position to cause
random disruptive turn-off spikes
during engine running. Since they are however in the power supply path
for the FI ECU, there will be a power filter located here, see below:
Solution Part 2b.
Location of Relays which trigger the symptoms:
Part of 1800ES Electrical panel with rectangular
Headlight Control
Relay
and Horn Relays. Located on inner fender on Distributor side of engine, partially obscuring the electrical terminals of
the Horn Relay, are Air Conditioning lines, so below, shown in the clear, is
what installing the snubber would look like.
Implementation of Solution Part 1. Adding Diode snubbers at the noise sources.
Refer to: Wiring Diagram Excerpt with Solutions 1&2 added
Diode Snubber Installation Notes:
1. Clean wires of Horn Relay with
carb cleaner or similar so
colors can be verified (terminal numbers should be double-checked with a light
and small mirror...this is no place for taking chances!), remove Brown wire from term 86 (30/51) of Horn Relay, and
install Orn Wire of Diode Snubber
onto same terminal, and replace Brown wire onto open terminal on paralleling
crimp on Orn Wire which was just
added. All push-on terminals should get a dab of
ACZP.
2. Remove Black wire from Term 85 and repeat process, for the
Blue wire of Snubber, replace
Black wire onto open terminal of Snubber.
3. Repeat the snubber installation process for the Headlight Control Relay
(terminals 15, Orn and
31b, Blue), present on all
injected 1800s, and Reverse Light
Relay (terminals 30/51, Orn
and 85, Blue) (present on earlier 1800E models).
Note: If symptoms are also
triggered by the Windshield Wiper Motor, and possibly even Windshield
Washer Pump, a snubbing provision may have to
be installed on each of these significant inductive loads! The first D-Jet owner
with such symptoms should make themselves known to the author, and I will work
out details for such a retrofit!
Snubber Diode installed on Relay (on the bench!).
BLU to Neg (85),
ORN to Pos (86) Observe polarity!
In the vehicle, wires originally connected to the terminals involved, will of course be on the open
terminals of the paralleling connectors, so when the modification is complete,
these wires will electrically be on the same terminals they came from.
From the Wiring Diagram, 85 will have a Black wire, and 86 (or 30/51) will have a Brown
wire. Assure correct installation by verifying color codes, and/or Relay
terminal number designation, with good lighting and small mirror.
[It's important not to get this wrong!]
Solution Part 2. Add back Filtering,
which has diminished over time, with a contributing factor possibly being the age-related decreased effectiveness of
electrolytic capacitor phenomenon, contributing to the increased sensitivity to
electrical upsets. This is an on-going and developing investigation
in conjunction with Dave Farrington's documentation of the D-Jet System.
With the well known, age related reduction of filter effectiveness, we can also add new power buss filtering external to the sensitive circuits to restore their ability to "ride-out" disturbances, and decrease their increased susceptibility to being affected by transient upsets. Checking the internal Wiring Diagram of the D-Jet ECU as part of a collaboration with Dave F, we find the following capacitors in the D-Jet ECU, their capacitance value, and circuit function of each of these capacitors, and, as well as evaluating their construction technology. The value of the retrofitted capacitor(s) which we will be fitting has been determined theoretically and verified experimentally, and found to cure the symptoms.
Adding powerbuss filtering external to the D-Jet ECU is clearly preferred to adding filtering internal to the ECU, as needing to add it internally would increase complexity and cost exponentially! Three external locations are used: 2a. close to the noise source, and 2b. close to the noise sensitive ECU. Part 2c. Filters the Alt Output, as well.
The Capacitor we will be adding are standard Bosch 0 290 800 052 Suppression Capacitors detailed below.
Implementation of Solution Part 2. Adding Power Filtering to a D-Jet vehicle:
Solution Part 2a (Adding filtering at noise source):
Noise Suppression Cap, modified with a paralleling crimp, shown installed
at
the Ignition Coil, with mounting tab tucked under the Coil Clamp, and connected
to Coil positive with the paralleling terminal.
Solution Part 2b (Adding filtering at power input to D-Jet ECU):
Noise Suppression Cap, again modified with a paralleling
crimp, mounted on a custom bracket (no new holes!) next to D-Jet associated Fuel
Pump Relay and Main Relay Fuel Injection
on inner fender, aft of Manifold Pressure Sensor.
Solution Part 2c (Adding filtering at power output of Alternator):
A third Noise Suppression Capacitor is added directly at the Alternator output, and from the B+ terminal to housing of the Alt as shown. Forward-looking Bosch engineers were once again sharp enough to include a mounting provision with Anti-Rotation Feature into the housing. An M6 by .7 thread (coarse) X 10mm bolt is used to secure the Cap, clocking the Suppressor against the ARF, and adding the wire under the nut on the nearby B+ terminal.
CAUTION: Since the wiring on this terminal is connected directly to the Battery and so (very!) live, Battery must be disconnected before this operation, lest you want to perform some unplanned welding! In-fact, it's probably good practice to disconnect the Battery before making any of the wiring changes of Solution Part 2, since there are Battery live wires closeby!
Note on the OE Alternator...both terminals on the diode mounting plate (at 7 and 11 o'clock in the pic below) are in fact B+ terminals, and are interconnected by way of the diode mounting plate!. On this 55A unit (sourced from the SWedish-EMbassy Component Collection and Spare Parts Horde, SW-EMCCaSPH) an insulated, protective threaded-on protective cap needed to be first removed from the upper B+ terminal so that it could be used as the connection point for the Noise Suppression Capacitor (protective plastic cap is visible next to terminal) .
Note also: If this upper terminal is not installed and available, for instance on a 35A Alt [need to confirm! It is not shown in the picture in Factory Manual, see below!], the NSC wire is not long enough and would need to be lengthened to reach the other terminal. Since this wire is powered, adding a secondary layer of protection (including thermal) in the form of fiberglass or PTFE (PolyTetraFluoroEthylene, aka Teflon) sleeving is good practice, and recommended!
Noise Suppression Capacitor in place on an OE 55A Bosch
Alt, securely mounted at the spot provided, and connected to one of the two B+
terms on diode plate. The "Hot Wire" to NSC is double insulated with a
PTFE sleeve. Terminal designators shown are lettered in their respective
harness colors.
Back of OE Alt from '71 1800E Factory Manual. Only one B+ terminal
is shown.
Wiring Diagram Excerpt with Solutions Part 1&2 added:
Chassis Wiring Diagram Excerpt with
Solutions Parts 1&2 added. (WDs for
1800E and ES are
substantially similar, but no Reverse Light Relay is shown fitted on the
1800ES WD!).
Violet is FI System Power routing,
and important FI System Power Return is
shown highlighted in Green.
The reader will notice that the Reverse Light, Horn, Headlight Control Relays, and even the Fuel Pump Relays are all configured as Low Side Switched circuits, and the Main Relay for Fuel Injection is configured as a Slave Relay to the Ignition Powerbuss.
Overall Conclusions and Summary:
As a result of the investigation into the multiple occurrences of momentary functional dropouts of sensitive systems by electrical upsets caused by breaking of inductive currents, it is my considered opinion that a two step correction is the way to address these issues, including preventatively, before they occur! A substantiated and peer reviewed explanation of the electrically induced upsets occurring in the D-Jet Fuel Injection System has been presented, and I will further modify and expand on my explanation as new info develops. An effective Two-Part Solution has been presented to address this issue with the goal of eliminating the trigger upsets of the electrical buss, and reestablishing the immunity of the D-Jet ECU to them, in order to continuing keeping these vehicles on the road and the fuel injection reliable. Both parts of the two-part solution must be installed for it to remain effective and vehicle reliable. If only Part 1 were installed, it is not reasonably assured with certainty, that the symptoms will not return, with a possible continued decrease in filtering...! I will be installing both Part 1 snubber diodes on the inductive loads and installing Part 2 powerbuss filtering preventatively as presented here on my own D-Jet equipped 1800 (because I have not personally experienced the above issues).
If the reader is experiencing D-Jet symptom which are not able to be cleared up by normal troubleshooting, service and maintenance of the FI System, and this MUST be the first avenue pursued, but which are concurrent with turning OFF inductive loads on the vehicle, and they wish to install the countermeasures shown here, contact the author. Symptoms must be reviewed on a case-by-case basis, and kits would be engineered for each specific chassis.
Making an Appropriate Kit Available:
I can provide a customized kit with the appropriate components to other D-Jet owners to "quiet down" power buss noise generated by inductive loads. This must be done on a one-vehicle-at-a-time consideration, and only after all other D-Jet troubleshooting options have been performed and it has been confirmed that this solution is called for! Please contact the author!
--------------------------------
General Maintenance (and prerequisites to neato scientific and complicated engineering solutions presented here!):
While we're on the subject of FI Sys Power quality...of course, the fuel injection system must get "good power" to start with! In addition to not including electrical upsets, this means minimum in-line Resistances...so if the Green wire on your super-groovy, and expensive, unnecessary(!), AGM Battery, which supplies power to the Main Relay for Fuel Injection*,and the D-Jet downstream, looks like the one here, you may not have the correct disposition to own and operate a vintage car! I recommend fixing your attitude, and that wire immediately, or consider selling the car as soon as possible to someone who does have the correct disposition and attitude!
[* actually, it's just a tiepoint...the Charging System supplies FI power, but FI current still needs to flow through that horrific connection with maybe half the strands intact!]
It looks like someone added a power connection for their cell-phone charger in
the K-Mart parking lot using only their pocket knife!...but no!...it's the main D-Jet
System Power routing cable termination, unacceptable and in need of immediate correction!
The negative return current side is no less important! There is no reason for FI System Power Return to be anything less than perfect! It is highly recommended that the securing bolt, and stack of connectors, be inspected for any deficiencies, cleaned to shiny metal, and reassembled with a generous anointation of ACZP, to keep these important connections at their best forevermore!
See also: Chassis Connections for D-Jet
Important
chassis return connections for the D-Jet Injection System.
To go along with the theme of making the D-Jet ECU incoming power as clean and electrically perfect as possible, both Negative Battery Cable, and Chassis to Engine Braid should also be preventatively checked, cleaned and made their best!
George Minassian picture of a Chassis to Engine Braid used with his kind permission. The car is in the process of restoration, and has likely not seen a single road-mile yet, so makes a very good example to show!
View from below, looking along exhaust pipe and forward.
Chassis to Engine Braid end
connections. Clean and tight (and anointed with ACZP),
should be the target for these important high current connections, which are subject to
vibration in service! [Very nice
work George!]
Reviewing the D-Jet Wiring Diagram (Sheet 2), the observant and qualified reader may notice that the Bosch designers actually included a Diode Snubber network for the Fuel Pump Control line (19), in the form of D554 and R557. Seen in this excerpt of the D-Jet circuit below, the reason for this snubber network is not so much intended to prevent the ECU disruptions we are concerned with in this investigation, but it is included to protect the internal T551, T552 Fuel Pump Relay control transistors from being subjected to the turn-off spike (transistors don't like these high-voltage spikes so much either! ...and Bosch engineers certainly did know they had to address that at the time of designing the system!).
Excerpt of D-Jet Circuit showing Fuel Pump Relay Control, and a relay turn-off
suppression network is included,
courtesy of the original, very capable Bosch designers. The D554 and R557
network is effectively across the FPRel Coil. D554 clamps the spike, and
R557 (68 Ohms) limits the peak snubbing current to a safe level for the diode.
(Reference Sheet 2 and the full
D-Jet circuit)
Dried Electrolytic Capacitors Notes and links from research:
Dried electrolytics are nothing new...they are a well known age related issue in the Smith's Tach! Link to: Age Related Problems in Smith's Tachometer
https://www.physicsforums.com/threads/older-electrolytic-capacitor-testing.966712/
https://en.wikipedia.org/wiki/Electrolytic_capacitor#Operational_characteristics
https://ac-blog.panasonic.com/relay/protecting-a-relay-coil-from-a-surge
Ignition and Other Capacitors...all the details one would ever need to know explained by some very capable and engaged individuals from the world of vintage boat motors! These enthusiasts are in much the same boat (no pun intended!) as vintage automotive guys who want to keep their point/condenser style ignition system:
From: https://wrcoutboards.org/magazine-articles/
https://wrcoutboards.org/wp-content/uploads/2020/04/Part1_Condenser_Construction_Failure_Modes.pdf
https://wrcoutboards.org/wp-content/uploads/2020/04/Part3_Sizing_Condensers_Correctly.pdf
Notes on Suppression of Inductive Spike (when interrupting the Current in an inductive circuit, like a relay coil):
https://en.wikipedia.org/wiki/Flyback_diode
Inexpensive Handheld Oscilloscope (used to capture and confirm the transient upset on the Ign Pwr Buss):
An inexpensive little instrument (Type: FNIRSI DSO152, at a modest ~$35!), but with portability and triggering features, and plenty fast enough to capture and hold the Ign Pwr Buss upset Before, and to show the success of our mitigation efforts, After minimizing it to the point that it no longer causes the D-Jet ECU to be affected by it.
Before screenshot from Paul D video capturing the upset of the Power Buss concurrent with release of the Horn Relay:
Toy 'scope (but actually perfectly adequate!) in use, confirming the nature of
the powerbuss upset,
and effectiveness of solution presented here.
Results of bench tests with toy 'scope:
Before capture, showing the huge negative spike concurrent with relay release...predictable as there are no suppression diodes in place originally!
Representative test setup on the bench, using a 9V Bat, SWF relay, and toy
'scope.
After capture, with snubber diode connected..."all's quiet on the western front!"
Diode Snubber effectively quiets down the back EMF spike!
Free-Wheeling Diodes and Relays:
Note that the terms Free-Wheeling, Quenching, Flyback, Suppression, Back EMF, Clamping, or
Snubbing Diode, can and may all be used interchangeably by the author, referring to
this component and its function.
Coil quenching diodes are nothing new!...good info on Digi-Key's Tech Forum: https://forum.digikey.ce om/t/component-options-for-relay-coil-surge-suppression/7789
Classic DC relay waveforms and a quick background:
Notice the waveforms shown are representative, and not necessarily to scale...depending on
circuit, and relay
inductance characteristics, back EMF generated according to the theoretical (v
= L (di/dt) can vary widely, but practically, and for the automotive relays
we're dealing with, 10-20 times the circuit V is not uncommon and unheard of.
That would mean originally the D-Jet ECUs of vehicles in Occurrences 2 & 3,
were able to deal with, and "ride out" turn-off spikes in excess of 100V!...but
no longer after 50 years!
Note also that a slight vestigial negative excursion remains of the spike with a Quenching Diode in place. This is due to the inherent forward voltage characteristic (Vf) of the diode, which is 0.5 - 1.0V, and must first be overcome before it can start conducting the spike energy and do its clamping thing...but when it does, the former mega-spike is clamped to all but nothing with the diode present...that's good, and most circuits are unaffected by what's left! Clamping diodes are a very effective way of quieting down inductive turn-OFF spikes!
Diode Type: Free-Wheeling Diodes used in relay coil suppression are typically 1N4007 (1000V PIV, 1A forward current rated, silicon). Other diodes (faster, higher power, lower Vf, groovier) have been considered, but diodes with those improved characteristics are more expensive, and just not necessary here! There is no need for a clamping diode to have better characteristics than the garden-variety 1N400X Series, and since we will be clamping a high voltage spike, it is good and common practice to use the 1000V version.
Link to component info: https://en.wikipedia.org/wiki/1N400x_rectifier_diode
Acknowledgment of Susceptibility to Power Buss/EMI Disturbances:
Volvo Service Bulletin - FUNCTIONAL DISTURBANCES E-engines from 1972:
Apparently, the factory had some encounters and experience with disturbances of the injection system caused by the breaking of inductive current of a relay...recall that a buzzer is simply a relay connected such that its own normally closed (NC) contact is wired into the relay's own coil current path, such that when power is applied, the relay picks, which opens the contact and current path, so the relay drops, which again closes the current path and the relay picks...lather, rinse, repeat, and you have a buzzer! ..but on the negative side, this arrangement is also a very effective electronic noise generator! ...and BTW, if you connect the moving relay armature to a diaphragm and move some air, you have a Horn!
"Functional Disturbances" is pretty vague description of the actual symptoms,
but the author proposes that momentary drop-outs of the D-Jet are right up there
with possible results...
Volvo internal Suppression Diode retrofit.
In the Fault tracing booklet, the "engine disturbances" causing rough running are also mentioned, and beyond being caused by the Seatbelt Buzzer, they also suggest it can be caused by external ElectroMagnetic Interference (EMI) such as generated by a transmitter, and everybody has one of those in their pocket now in the form of a cell phone! This ties back into the area of system filtering mentioned, and addressed above...
Discussion on (Antique Radio) Forum: Subject: Spike protection diodes used with Bosch automotive relays https://www.antiqueradios.com/forums/viewtopic.php?f=2&t=323850
Everything you always wanted to know about Relay Snubbing Diodes: Diode Turn-on/off Time and Relay Snubbing
Examples of Bosch Relays with Internal Suppression Diodes:
These pix and graphics where harvested from suppliers offering "Bosch" style relays...notice, that for those relays which have internal Suppression Diodes, some show the polarity [that's nice of them, because getting it right is pretty important!], others leave it up to the designer's/installer's awareness and smarts!
Diode is present internally, but no polarity is shown, although getting it wrong would
present a short circuit to the supplying circuit! Notice typical 10 digit
Bosch PN.
It's quite important when connecting Relays with internal clamping Diodes to get the polarity correct: Diode is connected in "reverse polarity", that is, with Cathode on the positive energizing voltage such that it will normally be non-conducting and "just at the ready" when the normal circuit energizing voltage is applied, and only conduct when the energizing current stops, as the reverse-spike is generated by the magnetic storage and discharge effect of the inductance. Cathode of Diode MUST therefore be connected to Positive voltage, and Diode Anode MUST be connected to Negative side.
Getting this wrong would mean that when voltage is applied the first time, for the purpose of intentionally energizing the relay, an inadvertent short circuit would allow unlimited current to flow through the diode, instantly sending it into electronic component heaven, but very probably not even blowing the fuse for the circuit(!), since the fuse is typically sized ≥8A in such a car circuit, and the diode is a small 1A forward current rated device easily killed by a fraction of the current allowed by the fuse!
The end result would be that the relay would subsequently even function as normal(!), but the spike-snubbing-function of the diode would be forever lost, and this would not be obvious or apparent without tests which check for this function! [...unless of course as in our case, the unsuppressed spike causes/triggers unwanted symptoms elsewhere...like the fuel injection system!]
Relays with suppressors:
Diode is present internally, in the Modern Relay, and the polarity is specified
and marked on the housing. A clamping diode is retrofitted externally to the
vintage Volvo Relay (actually manufactured by Bosch, Ströbel or SWF), and It
does the job splendidly, and every bit as well as one that was installed
internally by the manufacturer!
[...but just between me and the
reader, that is not a typical modern Bosch looking 10 digit PN so I expect this
part may be a
counterfeit!]
"Two-Diode Relays"
In the author's travels and research, I have also run across a relays with TWO diodes...what's up with that...? Answer: This is where apparently they have incorporated BOTH, but very different functions of spike clamping AND the reverse polarity protection...note the two diode version on these two BMW relays...and on one, the series diode is in the low side (85) and on the other, its in the high side (86)...this gives the engineers more design options...but makes following and understanding it bafflingly complicated for the electronic layman! Note also the price variations...it's enough to drive the non-engineer to drink! [...and we engineers drink Jägermeister (strictly medicinally it is understood) without needing such reasons!]
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"Two diode Relay" examples harvested from the internut!
These handy little marvels are well known to installers who simply need to add a connection to an existing push-on terminal (like on the relays), and they allow this without substantially changing the existing wiring. Simply pull the existing push-on terminal from the tab of your desire, add the wire, onto which one of these useful terminals has been crimped, and replace the original terminal onto the free tab of the paralleling crimp. Viola!
Paralleling Crimp
Scotchlock "insulation displacement aberration" terminal, used to add wire to
existing wiring (and add future intermittent connections into an electrical
system!)...these are used only by weenies!
See also: Notes on Making In-Line Connections
There's a lot of engineering in ceramic capacitors! See: https://en.wikipedia.org/wiki/Ceramic_capacitor#Class_2_ceramic_capacitors
Link to capacitor manufacturer Kemet's Data page on the X7R dielectric [there's that word again!]: ttps://content.kemet.com/datasheets/KEM_C1075_X7R_HT_SMD.pdf
[I'm no capacitor specialist, but apparently, this X7R dielectric is some groovy stuff!] See also: https://www.samaterials.com/multilayer-ceramic-capacitor-x7r.html
Reliability Bathtub Curve ("...not a joke!" J. Brandon):
Coming from Reliability Engineering circles, the RBC is a Failure vs Time graph with three zones, and named for its shape.
These zones are: Increased Early or Infant Mortality Failures / a low number of Random Failures during Service Life / and again an increasing number of Wear-out Failures at the End of Service Life.
Note: Thankfully, when Bosch was supplying the D-Jet Electronic Control Units, before delivery to customers like Volvo, Mercedes and the many other auto manufacturers who fitted this first FI system in widespread use, they would first subject ECUs to, and require them to pass, a "Burn-In" (this is a powered test for a specified required amount of time, with input and output stimuli to effectively simulate in-service conditions, and this test is run at elevated temperatures, even in some cases under vibration, to make it an accelerated, worst-case test). The Burn-In is intended to "weed out" early failures, so that when actually delivered for installation into cars, the ECUs were beyond their "Early Failure Period", and would give a long and trouble-free service life.
Indeed, even after 50 years, Bosch D-Jet was, and continues to be, a highly reliable engine control system, where the ECU is typically the LAST thing to be suspected of failure! But...age-related weaknesses are showing themselves with more and more frequency. Typical age-related problems of damaged or corroded connections notwithstanding, I believe this may in part be due to the well-known age-related wear-out mechanism of electrolytic capacitors, some of which may be reaching their EoSL, so the ECUs now need a bit of outside help to keep on giving reliable service!
This SW-EM Root-Cause Investigation is
ongoing and in progress, and the author will stay on top of this! ...D-Jet Operators: Stay tuned!
Source: https://en.wikipedia.org/wiki/Electrolytic_capacitor#Operational_characteristics
The Reliability Bathtub Curve...and a
rhetorical question!
List of Capacitors in the D-Jet ECU (034), and susceptibility (Electrolytic) disposition:
[DETAILS ARE IN DEVELOPMENT]
Color coding of capacitors used in the D-Jet ECU (by the author's evaluation, by C value - anything over 1.0 uF): Not subject to age-related degradation, Possibly subject to age-related degradation. This test is performed in collaboration with Dave Farrington's investigation and documentation of the D-Jet ECU.
Most capacitors are metalized polycarbonate, which is quite stable not particularly susceptible to age-related, but an ESR test performed on each was performed to see if any age related issues were revealed.
In-Circuit Tests of D-Jet ECU Capacitors. The instrument energizes the Cap under Test with a very low voltage, high frequency test signal, designed not to allow an evaluation of the CuT to be influenced by other components in the associated circuit.
Reference, C Value, Location, Function in circuit, Result of ESR test
| Reference Designation | C Value (uF) | Location (Farrington Dwg; Sheet, X,Y) | Function in circuit | Notes (ESR Test Result, Note 1. ) |
| C100 | 0.1 | Speed Compensation Ckt | Coupling | |
| "C102,C105" | 0.47 | |||
| "C101,C103" | 15 | |||
| C104 | 0.33 | |||
| C106 | 33 | |||
| "C200,C201" | 6800 | |||
| "C209,C212" | 1000 | |||
| "C301,C302" | 2200 | |||
| C400 | 2.2 | |||
| "C500,C501" | 6.8 | |||
| "C503,C602" | 1.5 | |||
| C700 | 3300 | Trigger Ckt Flip-Flop, | Coupling, Speed-up | |
| C900 | 10 | Mixture Enrichment Ckt, | ||
| "C901,TS2-Coolant?" | 2000 | |||
| C902 | 0.068 | Pulse Shaping Ckt, | Coupling | |
| "C903,C904", | 0.047 | Edge Detector Ckt, | Coupling | |
| C905 | 3000 | TPS Flip-Flop Ckt, | Cross-Coupling, Speed-up | |
| C906 | 2.2 | Pulse Shaping Ckt, | Filtering | |
| C907 | 100 | Pulse Shaping Ckt, | Hysterisis T902 |
Note 1. DCR/ESR test made with GME 236
Tester shown below.
Intermediate Conclusion on ESR test:
PLACEHOLDER
Bosch 0 290 800 052 Suppression Capacitors:
Several of these 2.2uF / 100V rated components were obtained for evaluation (equivalent components to the 0 290 800 007), and use in Solution Part 2. The 2.2uF value is a significant "Goldilocks Value", as it is high enough to filter effectively, but not so high as needing to be an electrolytic construction, therefore susceptible to aging issues, and to present a high in-rush charging current on first power-up on the output terminal (Term 87, FI wire 28) of the Main Relay Fuel Injection (MRFI) as to need current limiting or risk damaging the MRFI contact.
The suppressors are also packaged nicely as they can be mounted to nearby grounded hardware, with the pigtail getting connected to a push-on tab wherever necessary...the single female term they are manufactured with, can optionally simply be changed to a paralleling terminal for our application.
Bosch 0 290 800 052. The right angle spade connector has a nice clip-on
insulator for a high safety factor on what will typically be a live power
connection.
One suppressor had to be sacrificed in the SWedish-EMbassy Component Dissection and Invasive Evaluation Department, (SW-EMCDIED) to determine the technology of construction (...you know what they say about making a soufflé...). The capacitor inside was found to be (dry) wrapped aluminum construction type, not highly susceptible to age-related degradation...that's good!
Internal evaluation in progress!
DC Resistance/Equivalent Series Resistance Test of Bosch 0 290 800 052 Suppressor:
These are important parameters when it comes to our filtering requirements...DCR/ESR show minimum and well in the green region! A high ESR is one, if not THE, predominant mode, of age-related failures of the electrolytics...the other is decrease in Capacitance.
DCR/ESR test using the GME 236 Tester.
Adding a 5Ohm test Resistance in series to verify function and accuracy of the test equipment. The instrument reads 6Ohms and shows that IF a 2.2uF cap truly exhibited such an ESR, that would put it into the yellow "Suspect" region of the evaluation graph. Such a reading when testing a component would clue in the operator that the cap was possibly weak and ineffective in the circuit.
Successful calibration check of the GME 236 Tester.
-------------------------------
Volvo and ElectroMagnetic Testing:
Volvo, being a conscientious, engineering-driven company, has been aware of possible Electro-Magnetic Interference (EMI) on their cars for a while now...I specifically recall a picture of a 240(?) under a power transmission tower in association with both Emission and Susceptibility testing they were touting...I have been trying to locate that picture to add it here [have not yet been successful, so if a reader can help with this, TIA!], but simply searching for "Volvo EMI test under transmitting tower " I did find their more recent Specification Standard STD 515-0003 Electromagnetic compatibility, EMC Volvo Group for such testing, and requirements for compliance: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwip18PulbCEAxX4vokEHcsXBhMQFnoECBkQAQ&url=https%3A%2F%2Fwebstd.volvo.com%2Fwebstd%2Fdocs%2FSTD%2520515-0003&usg=AOvVaw0-8dnvU4cDTzzPNA8iQa_0&opi=89978449 ...so they are very aware that their cars need to function reliably in today's electromagnetically rich environment.
In particular, in this document, see:
Section 11. Immunity to conducted transients on supply lines
Section 15. Conducted transient emission requirements
--------------------------------
External material sources are attributed. Otherwise, this article is Copyright © 2024 Ronald Kwas. The term Volvo and names of other commercial suppliers possibly occurring here are used for reference only. I have no affiliation with any of these companies other than to keep their products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of their products here. The information presented comes from my own experience, research and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, or worshipped, at the readers discretion! [The Reliability Bathtub Curve is real, and not some sort of humorous SW-EM metaphor!] As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles, and future!
You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, 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 Harvard wants you! As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the unique metaphor and possibly (likely) wise-a** comment.
