Got back to the car today. Battery and turbo control unit disconnected. Checked for continuity from terminal 85 /R61 to a new ground jumper on pin 12 = no reading, nothing. Checked against terminal 86 /R61 (airbag) without ground jumper on pin 11 (alarm control) = 39 ohms. Connected ground jumper on pin 11 (alarm control) = 0.8 ohms.

It appears the ground jumper is working ok but no continuity on terminal 85 /R61. I then checked the brown/yellow wire under the fuse box going into terminal 85 /R61 and it has heat shrink on it.

Is this supposed to have heat shrink or is it a telltale its been meddled with before?

How to remove the relay socket to inspect the wires?

Cheers


Fusebox R61 terminal 85 (ground)




TCU plug pin 12 new jumper to ground

 

1. there is usually no heat shrink tubing on it, the cable has been "repaired".

2. the cables are plugged into the base of the central electrical plate from below with the usual cable plugs and can simply be pulled off.

3. the brown/yellow cable leads from R61 to turbo unit pin 12. It is only interrupted by the 6 pin connector T15 under the drivers seat.

4. it is not plausible that no ground is switched to pin 12 of the turbo unit AND the cable from pin 12 to terminal 85 on R61 is interrupted, because the car has been sat for a while after running fine. I would check this again.

Fritz

 

Hi Fritz, thanks for the reply. What is the '6 pin connector T15' you are referring to? Under the driver's seat is the Multifunction Control Unit (aka Turbo Control Unit 965 618 130 00) and the Control Unit Acceleration Enrichment (965 618 131 01).

I can't get a ground to R61 when using a temporary ground on pin 12 with all other pins plugged into the turbo control unit. And I can't get continuity the other way from terminal 85 /R61 to pin 12 when using a temporary ground - as per the photo.

Which one do I check again?

The car has race seat belts with a crotch belt that goes under the seat. I do wonder if the belts have rubbed up against the control units and dislodged or broken the wiring somehow. It seems odd as the car was running fine and only sat for 2 months after having the battery disconnected.

Cheers

 

According to the wiring diagram there is a connector T15 under the driver's seat where the cables from the BA control unit and the turbo unit come together. Follow the brown/yellow cable from pin 12, it leads to this connector.

I would check again if there are actually two different faults at the same time on pin 12/turbo unit and on the brown/yellow cable to terminal 85. That would be strange after 2 months of standing and should at least have a comprehensible reason for the cable failure.

​​​​​​Fritz

 

Ok, thanks I will take a closer look and check the connector.

Can I prove the turbo control unit is activating the ground for R61 by connecting a new wire into pin 12 and running it all the way to R61 and wrapping around terminal 85 on the relay - like we did for the temporary ground to the screw on the strut? Then plug everything else back into the TCU. If the car starts this would confirm the issue is in the wiring between pin 12 and the socket for R61?

Cheers

 

Yes, that's exactly how it is. According to the previous measurements at pin 12, it should not actually work. But it is worth a try..

Cheers, Fritz

 

Hi Fritz, it worked. I fitted a 3mm female connector into pin 12 of the TCU plug and ran a 4 metre wire to R61 and wrapped around terminal 85. Fitted relay and plugged back into the turbo control unit. Key ignition ON and it started immediately. Prior to this I also found the T15 connector but it appeared to be fitted tightly and made no difference when I unplugged and plugged back in.

To be sure I hadn't miraculously bumped something to get it to start, I plugged the original pin 12 back in. Same result, no start.

Is it safe to assume the TCU is working correctly but the brown/yellow wiring between pin 12 of the TCU plug and R61 is broken somewhere? Or further tests needed?


Female connector with 4 metre wire on pin 12 of TCU plug to R61



T15 connector


Cheers

 

Well, a little uncertainty remains. The question is why the switched ground at pin 12 was not measurable.

Despite, if it works with the replacement cable, I think the problem is solved for now. If you get stuck somewhere without fuel pressure, you know what to do. Put a jumper for the R61 in the glove compartment.

If you are looking for the interruption of the brown/yellow original cable, I would start at the repair point below the R61.

Cheers, Fritz

 

Well, I don't know whether to laugh or cry. When checking the wires into R61 under the fuse box I found another wire with heat shrink (another yellow/brown but connecting to a brown wire in the harness)...


R61 wiring


And when tracing it I found the reason why the wire on terminal 85 also had heat shrink - they are both wired into this...


Kill Switch

Of course I was fully aware of the switch (it was needed to track the car) but didn't know until now it was connected to terminal 85! Never given me any trouble in the past and I did turn it on & off a few times initially when car wouldn't start. But tested it and sure enough it's only working intermittently. Played with it a bit and the car fired up - sometimes you can't see the wood for the trees!

Replacement switch on the way. I noted there wasn't a brown/yellow wire going into the harness. The kill switch was connected to terminal 85 and a brown wire that disappeared into the harness. But it's definitely a brown/yellow wire at pin 12 on the TCU?

And for those that really do have a faulty TCU I got a reply from www.ecu.de that they do not offer a check and repair. But https://www.cartronic-motors.com/ replied "The test price is 89 Euros include tax, after that i can tell you exactly what is wrong, but i have to test both ecu's, Immobiliser+ECU units".

Fritz - thank you again for all your help. It's truly appreciated.

Cheers

 

Hi, we are in the same boat, I would have had to come up with it, at the latest when I saw your picture with the patched cable. I installed a similar solution in my car as an immobilizer / anti-theft, not at the relay but at the output of the TCU.

O.K., if the second pin of the switch is connected to a brown cable that disappears in the wiring harness, I suspect that there is permanent ground. Brown cables are used in automotive harnesses almost exclusively for permanent ground. This is easy to check, if I am right fuel pumps must run when the ignition is on. Which is not that great.......

The brown/yellow cable on pin 12 of the TCU can then simply remain open, without function. Which is probably what the measurement showed.

Maybe one of the previous owner has installed that solution because of temporary difficulties with the Pin 12 ground and for having a hidden immobilizer, who knows.

Thanks for the feedback regarding ECU and cartronics, is also interesting for me.

Cheers, Fritz

 

Just a quick update on this - car is running fine. I still can't find a brown/yellow wire going into the harness under the fuse box but haven't dug too deep for fear of damaging the wires. But the fuel pumps only run when the engine is cranking as they're supposed to, not when the ignition is ON. So despite the kill switch wiring everything appears to be in order.

On a separate note, I need to replace the clutch and possibly the flywheel. However my workshop manual for 1991 Turbo has some sections missing. Can I trouble someone for a link or Dropbox etc to a full workshop manual?

Much appreciated.

Cheers

 

I think I have all manuals all sections - it's a lot of PDFs. What's the easiest way for me to upload them somewhere these days...

 

Thanks Wicks, that's very good of you but the ever helpful Fritz (thanks again) has already sorted for me.

Cheers

 

Ok so it was the flakey Kill Switch causing the issue all along, right? Yes not sure, if I were you, I'd be laughing or crying or fist pumping. Glad to know it wasn't an actual electronic component of the car - such as the the TCU. Some piece of mind...

 

Yep, a faulty $10 switch sent me down the rabbit hole! But on the bright side, thanks to the good people here, I learned a lot.

Cheers