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Everyone,
I have been using a '88 740 NA w/ Bosch ignition (295k miles, M47 transmission) as my commuter over the past year and recently I have been having trouble with warm starts. Increasingly the car will not start when warm on the first try...it will crank and crank but not start, not even a cough. I then stop cranking, wait a few seconds, and then retry and she will usually start but will have an oscillating idle (+/- 300/400 rpm) until she is driven a bit. Once moving she drives fine and she has never had any trouble with cold starts. This problem has been very intermittent but has been happening more frequently as we head into winter. Finally, just this last weekend she wouldn't restart after a stop at the gas station. I had to wait about 15 minutes or so until she finally roared into life.
The only other symptom I have is that recently the idle quality has becoming poor. I had set the idle to 800-900 RPM and sometimes she will idle fine at that speed. However, at other times when I put in the clutch in the RPMs will drop very quickly, dip below 500 RPM (causing lights to dim) and then catch and she will idle very low, about 600-700 RPM, with some oscillations and hunting.
To debug this problem, I have done a few things:
- I have checked and I do feel the main FP relay in the center stack clicking when it fails to start. I have also tried a different FP relay to no effect.
- I have checked with a timing light that she does get spark when failing to start.
- Feathering the gas pedal does seem to help a little, but not always. I tried cleaning the IAC and replacing with a known good unit...both steps did not help the problem.
- I also pulled in the intake bellows and did a light cleaning (a throttle body gasket is on order to do a full cleaning).
- I verified the idle switch "clicks" when the throttle plate is closed.
- I have opened the gas door while it is running and I can't really seem to hear an in-tank pump running...only gurgling of gasoline being circulated. I then tried jumping the pumps and then pulling the in-tank pump fuse, which had no effect on the sound of the pumps, so I likely have a dead in-tank pump (although I don't know why this would cause a no-start).
- I have checked for vaccuum leaks and replaced a handful of vaccuum lines but this didn't help
- I have checked for leaking fuel pressure regulator (by pulling the vaccuum line) but I didn't see any issues.
I am looking for what else to check further when I have time this weekend to poke around. What are the most likely candidate items to check? Anyone else have similar warm start issues? Is it possible the in-tank pump is the cause of the warm start tissue? It seems like a strange manifestation of a bad in-tank pump, since she runs fine at WOT.
Thanks,
Brian
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