L-Jetronic ECU connector pinout

[furgo]

I've been diagnosing and testing the fuel injection again, and I thought it'd be time to finally finish off the diagram I created a while ago, which I have been using as a reference for my '79 bus.

While researching on each input/output/power signal, I've come across a few that are specific to particular model years only (or California variant).

I first put all signals combinations on one master diagram, but I thought it would be easier to use separate diagrams with only the relevant signals for each year. I'm providing the two versions. Pick what you need (or what you like).

I've got a few signals that I could not work out, as I don't have access to the ECU of the relevant years. I've marked these in red as "TBD". In particular:

• '75-'76, '79 CA bus diagram: the full throttle (or WOT), two-pole switch has one side connected to pin 3, which is the actual input to the ECU. I don't know which voltage is applied to the other side on pin 18. It might be open, 0V or +12 V. Judging by the high altitude switch applying +12 V when closed, I guess that it's +12 V, but I don't actually know. Update: looking at the D-Jetronic ECU schematics, the other pole of the switch might actually be GND.
• '79 CA bus diagram: on pin 28, I believe there needs to be GND for the fuel pump to be properly powered, but again, I don't know without having checked the actual connection on a '79 CA ECU.
• Update– All diagrams: I noticed that on my bus the pin 20 connection (Fuel pump running) is actually N.C. on the ECU side, even though the harness has the wire coming into it. This means the ECU does not actually use that signal on a '79 bus (it neither does on a '75). It would be good to confirm if that's the case for all other years. I'll update the '77-'79 diagram with this finding later on.

I'm all set with the diagram for my own bus ('77-'79). If someone happens to want to help others to complete these other years' diagrams and measure what these signals actually are, I'd be happy to update the diagrams with the results.

I've classified each diagram grouping the changes I saw belonging to each year. I'm not sure if separate pinouts were necessary for pre-'79 CA buses, though.

Other than that, as usual, feedback and corrections will be greatly appreciated.

Thanks!

_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[aerosurfer]

Nice graphic indeed. I would add to each of the years the associated ECU part number. It has been discussed, that they are interchangeable, but for anyone searching what they might need or have, we all know that year of the bus means little compared to what’s actually presently in there. Like your discussion about AFM part numbers in the other thread, the differences between ECUs may be nominal for tracking what came with what model year, but it gives clarity to the user.

From Ratwell
http://ratwell.com/technical/FISwap.html

ECU parts numbers:

Model Year
California Manual California Automatic Federal Manual Federal Automatic
1974 n/a 022-906-021K n/a
1975 022-906-021L 022-906-021M 022-906-021H 022-906-021J
1976 022-906-021Q 022-906-021R 022-906-021N 022-906-021P
1977 022-906-021AA 022-906-021AB 022-906-021S 022-906-021T
1978 022-906-021AE 022-906-021AF 022-906-021AG 022-906-021AH
1979 039-906-021D 039-906-021E 039-906-021B 039-906-021C
Vanagon 071-906-021B 039-906-021E 039-906-021C
_________________
Rebuild your own FI Harness..My Harness

77 Westy 2.0L Rockin and Rolling Resto!

72 Sportsmobile (sold)
79 Tran$porter... Parts car money machine (gone)

[furgo]

Good call, thanks. Adding ECU part numbers instead of model year would make the diagrams more useful indeed.

The challenge I've got here is that I don't have access to or info on any ECUs other than my spare one.

I could do an educated guess at assigning ECU part numbers to the diagrams if:

• Someone would know the reason why there are different ECUs for automatic vs manual. It might be an obvious answer to some, but I've got 0 experience with automatic.
• Someone would know why there are pre-79 different ECUs for Federal vs. California (on 1979 it's clearly at least because of the O2 sensor)

In terms of the "TBD" pins, if folks are interested to find out what they are for their ECU, perhaps someone could step up to:

• Remove the ECU connector and check if there is a pin 20 present or not
• Measure the voltage at both ends of the full throttle switch (if there is one), with ignition key on.
• Measure the voltage at the double relay's pin 85, with ignition key on, on a '79 California bus,
_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[aerosurfer]

I think it comes down to the Harness and the associated equipment on the motor.

I swapped my -s ECU with an -AH one when mine had issues with no change in performance even though I was not using the full throttle circuit that the earlier systems had.

If you look at the wiring diagram for the ECU and harness on page 41 of the AFC manual it makes no difference to all the federal models. 79 Cali is on page 42 With discernable differences.

https://www.thesamba.com/vw/archives/manuals/afc_f...Manual.pdf


More very good ECU and AFM info reading from long ago..... Particularly what Karl says!

https://www.thesamba.com/vw/forum/viewtopic.php?t=301261&highlight=ecu
_________________
Rebuild your own FI Harness..My Harness

77 Westy 2.0L Rockin and Rolling Resto!

72 Sportsmobile (sold)
79 Tran$porter... Parts car money machine (gone)

[furgo]

[Randy in Maine]

I am not sure if the 79CA actually had a rev limiter in the ECU. I had a PM discussion with both Karl, Boston Bob, and Ratwell and I sort of remember that
no conclusion was actually drawn and I am not sure it even matters.

I do know that the 79CA set up (as well as the vanagons CA models) did not use a series resister as that was done inside the ECU.

[SGKent]

for a fact the 1977 - 78 CA does have a rev limiter. Have hit it a couple times when testing the engine. It basically cuts the fuel off to the injectors so that the catalytic doesn't suffer from lean misfires. The injectors can only flow a certain amount of fuel so at some RPM they flat line, and any additional RPM goes lean. I would suspect that the 1979 and later California models do too.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[Wildthings]

Great idea, thanks for the effort you have put into this.


I would suggest using standard VW wire colors where possible:.

Brown for grounds

Black (or dark gray) for the switched ignition circuit (#15) (Not sure this is actually ever used on a Bus ECU)

Red for the B+ constant 12V circuit (#30) and for power coming to the ECU via the double relay.

[furgo]

[furgo]

I've correlated the VW part numbers with the Bosch part numbers to get some more information from the Bosch ECU parts list. I translated the part descriptions and then added them to the original table.

Some things to notice:

• The Bosch documentation is not very consistent in describing which functions an ECU part # had. Also some key capabilities such as injector current control of the '79 CA ECUs were never listed.
• There were separate part numbers for ECUs going to the Swedish market too.
• From the descriptions, some degree of interchangeability can already be inferred.
• The first ever Type 2 ECU (1975, CA Manual) seemed to have all available functions except for Lambda control (which had not yet been on the market). Subsequent ECU parts removed or added functions as necessary. This lead to an explosion of part numbers, but it must have been cost-effective enough to justify it. There are even more ECU part numbers in the Bosch parts list, but I've focused only on the known ones from the original Karl table.
• I've translated the different ECU functions from some other Bosch document. They're described below.
• Being quite honest, I don't quite understand what the anti-bucking (Anti-Ruckeln in German) circuitry does, but it seems to have been an internal circuit in the ECU that acted upon particular changes of air flow and engine speed.
• A couple of ECUs have acceleration enrichment capability. I don't know how acceleration was sensed, unless a throttle position sensor (instead of the WOT switch) such as the D-Jetronic one was used. The ECU could have sensed the rate of speed change, but there were limits to what a bunch of discrete components could do, this was not a microcontroller-based ECU.

Full load enrichment – when a full load event is detected via the Wide Open Throttle (WOT) switch, the injector time is extended to enrich the mixture (WOT switch, ECU).

RPM limiter – fuel injector pulses are stopped at engine speed values higher than 5400 RPM (ECU).

Intake air correction – In order to compensate for the physically induced measuring error of the air flow meter, the injection time is corrected as a function of the intake air (Air flow, TS1, ECU)

Acceleration enrichment – Upon acceleration with the gas pedal, a temperature- and time-controlled fuel enrichment takes place (TS2, ECU)

Post-start enrichment – After the motor has started, an additional quantity of fuel will be injected as means of enrichment, that will be dependent on time and engine temperature (TS2, ECU).

Anti-bucking – When bucking occurs, it is assumed that the load changes are smaller than in an intended acceleration. If a load change occurs below a certain threshold value, the control variable will not be the newly calculated value of the slightly changed load, but instead it will be an approximation of this new value (Air flow, engine RPM, ECU).
_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[SGKent]

the ECU is analog. It is not a computer with software programming. It takes the square/sawtooth wave generated the coil primary, shapes and amplifies it then uses that to open and close the injectors. All other sensors add time to the period the injectors are open depending on what the sensor sends to the ECU. The only smart logic it has in a sense is to know which way the AFM door is swinging and how fast. That is how later models know to add extra fuel for acceleration.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[airkooledchris]

[ve7kilohertz]

Hi Furgo et al,

Are you still working on this project? I may be able to contribute to your research as I am piecing together a L-Jet system for a 1.6 or 1.7L engine. I have 2 ECUs from buses, both I have apart to see what differences there are, 022 906 021AG and 022 906 021S. I also am working on figuring out differences in AFM's over the '76-'83 years. I have a couple of each of 6 pin and 7 pin, '76, '78 and '83. 006 012 and 030.

Cheers

[furgo]

Hey,

thanks for the offer. While I'm currently not actively working on this, having some pictures of other ECUs would definitely be interesting.

Other than that, the same unanswered questions of the first post remain. To recap:

• Pin 18: is it +12V? Need either '75, '76 or '79 CA ECU (or bus) with WOT switch to confirm.
• Pin 20: is the "fuel pump running" signal unused (i.e. open pin or no pin present on the ECU connector) only on '79 Federal ECUs or on all years?
• Pin 28: is it permanent GND? Need '79 CA ECU/bus to confirm.

If someone with that configuration could contribute, then the pinout diagrams would be complete.

Looking them up on the table your ECUs seem to be:

022 906 021 AG - Federal manual '78
Model 78 Sweden, same as 022 906 021 A (Model 77 California, with RPM limiter), but with acceleration enrichment

022 906 021 S - Federal manual '77
Model 77 USA, without full throttle correction
_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[Tcash]

[ve7kilohertz]

Tcash,

Excellent info and drawings, explains a lot and is very helpful. Thanks! Where did you find this info? I have been looking on line for a while now and have not seen some of these drawings.

Cheers

[ve7kilohertz]

Here are the 2 ECUs I have. Let me know if there is anything else you want pictures of. Cheers

[furgo]

[Tcash]

[ve7kilohertz]

Thanks for the picture, looks completely different with more modern ICs.

TO-3 power transistor is ON503, 7637 is the date code. The IC's in mine are TO-5 package, I suppose I could pull the heat sinks to get the part numbers but as they are proprietary, probably no point. Hopefully these ECUs work, one was marked NFG, but after close examination of the traces on the bottom, I found a couple of solder bridges between wires passed thru from the top side, and pads. Not sure if that was an intentional connection or not. ?? Pretty poor QC in my opinion if they are not supposed to be joined. Would be good to find another similar ECU type to compare. Here is a picture of what I am referring to. In the top side photo, you can see the wires soldered and passed thru to the bottom layer, 2 of them were "joined" to pads on the bottom, which looked like solder bridging, the others were all just bent over but not soldered, maybe test points? Maybe different connections for vehicle or sensor variations? I used to work in a SMT contract mfr and that's all we did, stuff thru hole and SMT circuit boards for various mfrs and I have a fair bit of experience in QCing this type of circuit board.

Thanks Tcash, that is an impressive collection of data! Hadn't seen that post before.

Cheers