L-Jetronic ECU connector pinout

[furgo]

Thanks for the transistor part numbers. Same ones as on my other ECU.

I'm not sure which ones you mean. I only can see this solder bridge I marked on the picture, and it's for two pads joined by copper, which should be connected anyway:

Or do you mean the wire bridges? Those were usually there to be able to have different functional variants with only one PCB design, which would reduce the extra initial costs of producing a totally different PCB for each variant. The additional cost of the variants would then only be during component placement (automated or manual on those days).

They should be totally OK as they are, unless someone fiddled with them after taking the ECU off the bus.
_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[ve7kilohertz]

[furgo]

[ve7kilohertz]

Hey Furgo,

I completely agree, which is why I only de-soldered 2 bridges, and why I marked them so could reverse it, which I will now do. I measured the injector driver ON503 and checks fine, there may still be nothing wrong with it and could have been a bad sensor or something the previous owner missed, I won't know for sure until I can find a vehicle to check it in. After I thought about it, the ECU must have worked for many years before it or something else crapped out, so the solder bridge removal was an incorrect decision on my part.

I am actually planning to connect the whole system, with injectors, AFM, AAV, TTS, CSV etc and then connect my pulse gen to pin 1 like you suggest, to see if I can get the injectors to fire real world, but without gasoline. Not sure how the driver xstr would like firing into no load? I'll put a 2,200R in place of TS1 as well.

Cheers

[EspenT]

[img]Hi
My first post on this forum. I have near zero experience with old VW but have good knowledge about engine management and have some electrical skills. I’ve been lucky a couple of times before and have managed to repair a couple of ecu’s and a few other things.
A local club for old VW’s has reached out to me for help with a ECU they suspect is bad. I agreed to have a quick look at it. I have problems finding schematics and data sheets to assist me. This forum seems to be very knowledgeable and you are hopefully able to help. Since my question is very relevant to the discussion in this thread I hope that it is ok that I ask my question here instead of opening a new one.
The ecu is a 0280000139 from a for me unknown vehicle.

I suspect that the power transistor on503 is no good.

Following picture show diode test from emitter to base. I did not expect continuity here. Base emitter is 0.6v. Base -> collector and emitter-> collector are also 0.6v. Collector-> emitter and collector-> base gives OL.
Could anyone confirm if this is expected behavior or not from this component ?
Measurements where taking assuming that the left pin/screw is collector. The lower/middle pin is base and the upper right pin is emitter.

Best regards
Espen

[telford dorr]

For testing purposes, a disconnected transistor looks like two diodes wired back to back, with the junction between the two being the Base terminal. Thus, with an ohmmeter set to the "diode" ohms range, and one ohmmeter lead connected to the Base terminal, the other lead will show conductivity to either the Collector or Emitter terminal. Reversing the polarity of the ohmmeter will show no conductivity. Bad transistors will either show no conductivity in either direction, or conductivity in both directions. For NPN transistors, conductivity will occur when the Base is positive relative to the other two terminals; for PNP transistors, it's the opposite.

To determine which terminal is which, Google a TO3 transistor package pinout.

I don't think there's anything really special about the transistor driving the injectors. Anything that can handle, say, 15 amps at around 100 volts should work. Back when these units were designed, transistors weren't nearly as stout as units commonly produced today.

In a pinch, while it's only rated at 60 volts, I'd try the ubiquitous 2N3055...

(That said, I should put a 'scope on the injector drive terminals and see what the actual operating drive pulse looks like...)
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[furgo]

Hi Espen,

Welcome to The Samba!

We should probably create a new, ECU-specific thread to keep things tidy, but I don't see anything wrong with discussing it here.

A few things:

• Looking at the ECU table in this thread, yours would seem to be for a '76 Federal bus
• You mention that the owner suspects that the ECU is bad. I would try to confirm this (*) before starting to chase an issue that might not be there.
• Usually component tests are not always reliable unless the device under test is removed from the circuit. Telford has already gone into detail on this and on transistor testing.
• You already got the transistor pinout correctly, but for others watching this, at least Emitter (E) and Collector (C) are marked on the PCB's silkscreen printing.
• There are no schematics available for these ECUs. However you can reverse-engineer some parts of the circuit fairly easily. Notice the stress in "some". Doing the whole PCB would be a much bigger project and not entirely possible due to the unavailability of datasheets for the three ICs.
• I mention this because if you suspect there is an issue with the power transistor, part of the circuitry associated can be traced. IIRC, the base is driven by one of the ICs with the round heatsink; the collector is connected to the injector pins directly; the emitter goes to GND. An RC circuit pulls the base to ground, I seem to recall. I can try to find the notes I took on my ECU a while back.

(*) Here's how I'd do a quick test on the bench. If you don't have an oscilloscope, an even easier test is to put the ECU on a bus. But even if you can swap ECUs in a working bus, I'd do test 1. on the bench before, to rule out any shorts on the unknown ECU first.

[EspenT]

[furgo]

Excellent, let us know how it goes!
_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[EspenT]

Decided to make a quick test circuit for the transistor. Seems to be working so I will try ECU as it is in the bus.

I’m able to adjust from 0-4A which is max for my supply.

[telford dorr]

PLEASE put a current limiting resistor in series with the base lead and collector lead! Accidentally turning the pot all the way up will toast the base-emitter junction for sure, and could likely cause the collector current and/or power dissipation to exceed max ratings.

[Ironically, back in the '60's, when transistors were new and not well understood, experimental transistor circuits in electronics magazines almost never had current limiting resistors in their circuits. Probably a left-over mentality from vacuum tube design, where short duration blunders weren't necessarily fatal. I wonder how many builders fried their expensive transistor by turning a pot all the way up?]
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[EspenT]

Connected blue probe to ECU pin1 and Yellow probe to pin32.

Injector seems to be grounded for 5-6ms. This should be enough to get some fuel?

[telford dorr]

[furgo]

Could you tell us more about your setup? E.g.

- What's the frequency of the input signal? I too would be interested to know the positive peak value -and if you used a probe with attenuation to measure it.
- Does the output signal get halved to actuate the injectors, as expected?
- But essentially... are you measuring on a running engine or on the bench? Otherwise the question of whether there is enough fuel to run would seem to be obvious .
_________________
'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[EspenT]

[furgo]

[RawUmber]

[RawUmber]

[KTPhil]

[furgo]

Thanks for contributing to figuring this one out. In the meantime, I had created a new, single diagram to rule them all, but I've just realized I never posted it on the forum. Here it is:

Some notes:

• It should cover all '75-'79 busses, including California.
• Pinout viewed from the harness side now, as that's where testing is generally done
• The points below still apply: