RESOLVED: '87 Carrera dies, no start

olivertwist · 04-10-2020, 04:49 AM

There are so many threads on this issue, many dating back over a decade, so for sure this has been covered and there's a ton of great information out there. However, due to the sheer amount of info, all the various tests, comments, etc., sometimes the solutions are buried in pages of info, so I thought I'd make a quick post, as I successfully fixed the issue last night with the help of info gathered on this forum. I almost gave up, until I came across of couple key pictures from @mysocal911 Thank you!

Issues:
First, under acceleration I experienced what seemed like a brief and sudden fuel cut off. Later that day, I turned into a gas station, and the car suddenly shut off. Coasted to the pump, filled up, started fine. A few days later, started it in the garage, ran for a minute, died, and then crank no start. Same a few days later.

Troubleshooting:
I started with the DME relay. Inspected it, didn't see any bad solder joints (to my untrained eye anyways), but decided I should have a backup anyways, and sprung for the Focus 9 solid state relay.
Installed, issue not resolved. I turned the ignition, and heard the fuel pump priming, so I then tested the sensors from the ECU plug - pin #8 and #27, #25 and #26, as well as the CHT in the engine compartment. White plug to ground on intake manifold. All Ohms were within spec.
As @Steve W has said, if the DME relay is replaced, then the probability of the cause is approximately 80% the Motronic DME unit itself. I opened the ECU up, and checked all the solders for any broken joints. Again, the untrained eye, and BTW there are a ton of solders. Starting to lose hope.

Solution:
Thanks to @mysocal911, there are really three critical circuits to look at. Open the ECU, and take the back metal plate off. Check the three solders in these pictures. Upon close examination, I could barely make out little hairline cracks. I reflowed some solder over them, reinstalled the ECU, and problem solved.

To save everyone some time in troubleshooting, my takeaway is this - DME relay first, if not resolved 80% of the time it's the DME ECU, check those three solder joints. If you're unsuccessful, well then you still have another 10% ref/rpm sensors, 10% misc (wiring, ignition switch, head temp sensor, etc) chance that you can track down.