Re: Diagnosis for stalling? (archive)

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I'm assuming that a fuel leak indicates that you have fuel pressure, so I'd be surpised if a pump is the problem. In some respects, it almost sounds like vapor lock. Have you checked to see whether you get pressure in the fuel tank (removing the gas cap and listening for either postive or nagative pressure)?

The fact that this string of events seems to be linked to running out of fuel causes me to believe that there may be some relationship there... I've found that with the 750, your wallet will thank you a thousand times over for eliminating the obvious before you start assuming that the complex electronics or mechanics are at fault... they usually are not.

If a vapor lock related issue turns out not to be the cause, I had been wrestling with a random stalling problem with some 'similar' symptoms on a 92 750 for almost a year and finally licked it. Here is what I learned in my pursuit of an answer:

1) Since the symptoms tended to create a binary i.e. on or off scenario, I finally figured the problem was likely a component that was common to both sides of the motor. This eliminates a lot of potential stuff like fuel pump relays, EML relays, DKs etc. since there is duplicity in these systems, one for each side of the engine.

2) After reading a post on the E31 board about a similar stalling problem I focused on the temperature sensors that give the FI information about the engine temp. While there are two of them, they both speak for both sides of the motor.

3) After replacing the 3 terminal sensor on the coolant crossover tube, part number 0 280 130 056, my stalling ceased... until I mistakenly swapped the intake air sensor wire with the engine temp sensor wire (passenger's side) and then I got random stalls again after the engine warmed up. Now all sensors are talking to their correct engine management component and things are fine again. I did replace the 2 wire temp sensor for good measure, but did not notice that it was a factor in the stall symptom.

Last week I had to use the wife's van to haul the boat around, so she drove the 750 for 3 days. Two days she left the headlights on and killed the battery, and I am ever so thankful for the discussions on the board, lest I would have no clue about getting into the car. But the key in the passenger side worked fine, and I later turned it backwards and synchronized the lock again. The third day she ran out of gas. I took some over and it cranked right up and ran fine. It ran fine for me after that.
Two days later (Friday) I needed the van again and she drove the 750. She was on the interstate, perhaps had just let off the gas at her exit, when the motor died and would not restart. A half hour later she tried one last time before calling the wrecker and it cranked fine and ran fine for another two days.

Today (Sunday) I drive about a mile to drop off my daughter and stop at a stop sign. As it comes to a stop it stumbled for maybe two seconds and dies. The tach was already idling, droped to zero, back up a time or two then stopped as if I had turned the key off. I tried to restart, the motor spins over smartly but does not fire at all. I waited 3 or 4 minutes, listened for the fuel pumps but traffic was too noisy, still no firing even though the starter spins fine.

Can't seem to get codes to read. Foot too slow? Have Check Control message. Like I do every day or two for three years.

Any suggestions? What about a fuel pump relay? But there are two on a 750, so wouldn't I be running on 1/2 engine instead of dead as a mackerel? I replaced one fuel pump last year. I smelled gas a couple of times last week while driving, but can find no evidence when I stop.

Anyway, any comments or suggestions would be appreciated. I have a Bentley and will soon begin tinkering, but since it runs fine now, I am not sure where to begin to diagnose.

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