ECM Gone Bad?
 

Hey fellas/felletes,

I am trying to diagnose an intermittent/no-start issue that I'm having in my '88 Carrera. Seemingly, out of the blue, my car decided to leave me stranded. The car cranks perfectly fine, but it will not start. Let me explain what I have found out before we start with the usual suspects.

1. The DME relay is brand new.
2. The speed sensor, reference sensor, and CHT sensor are probably four months old.
3. The car WILL start on rare occasions. When it does, it seems to run perfectly fine. There is no stumbling/stalling/hesitation/etc.
4. I tried to check for spark by pulling a plug wire, and connecting it to a grounded plug. I saw no spark, but that's the first time I've done it, and the spark plug was from a different car altogether, so I may have done something wrong.
5. I could never hear the fuel pump working, so I got under the car, and held the fuel pump while my girlfriend cranked the engine. Sometimes, the pump would vibrate, but sometimes it would not.
6. I tried to do some testing on the ECM according to the Bentley Manual, and found that there was no power going to the fuel pump. I still have some testing to do, though.

I'm beginning to think that the ECM may actually be bad or going bad, but I have no one around here that has one with which I can swap. Either that, or the fuel pump is going out, and I did the spark test incorrectly.

If you have any thoughts or suggestions, I'd sure appreciate it. Thanks in advance.

Aftermarket radio? Alarm?

Check the alarm control unit. I spent $250 to have the computer checked and it turned out fine (but I did get a SW chip out of the ordeal...) went through checking all wiring and found the alarm control unit, opened it up and so be it a broken solder joint. If I jumped the fuel pump it would worked fine. As soon as I resoldered the alarm control unit it ran great with no fuel pump jumping :)! The radio in mine was redone.
The alarm control unit is on PDF page 445/474 or Diagram 910-00
the part is #3 in the diagram.

I had similar symptoms, one or the wires going from the engine compartment to the dme disconnected. This is likely not your issue, but you never know. It even had my mechanic stumped for an hour because he never thought to look there.

Loren at Systems Consulting can test the DME before repair. It's probably worth checking

It is pretty likely that it is the DME. If you know someone with an 84 thru 89 Carrera test it by plugging your DME into their car. There is nothing in the DME that will burn up stuff in a car but there are a couple things that could conceivably burn up parts of the DME.

If it is the DME (and it probably is) the common failure is for the solder connections to break down. They just resolder the board and you are good.

Try another DME relay. I had a new one that had issues and did the same as yours. Put in another relay and all issues went away.
Tom

Mine turned out to be the factory alarm gone bad, do a search and you can see how to bypass it. It has to be DME or alarm going bad. Bypassing the alarm is easy and cheap, can't say the same for the DME.

Well, I don't have a factory alarm, so I guess I know my next step. I've tried three different DME relays with no change. Unfortunately, I can't just swap one because I don't think there's another Carrera within 150 miles of me. How much does it typically cost to have the ECM tested? I know it's $400 - $500 to replace. :(

Call Loren tomorrow. He can give you a price. It is rather reasonable.

Just fixed mine for the second time.

For testing you can also consider ischmitz, 3.6@cox.net

+1

Specialized ECU is in my backyard so I used them. All of those referenced in this thread are good.

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