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My wifes '91 745 has been giving me fits the last few days leaving her stranded with an intermittant no-start. Here's what I found and the possible solution. It's a little unusual so I thought I would post it here as it may help someone else in the future.
Problem: Intermittant no-start. Leave it a while it will start. No trouble codes. Fuel pumps cycling with key-on. Replaced main relay and FI relay, then found after cranking it a few times it would stumble then finally start. Fuel was just below 1/4 full, so I suspected problem with the in-tank pre-pump, but again, I could hear it running when the engine started. She had the same issue the end of last week and I thought it may have run out of gas, but it started a few hours later and the gauge was reading just under 1/4. Thinking the gauge was wrong this time, I filled the tank: just over 11 gals so I knew it wasn't out of fuel: just low. Went back to suspecting the in-tank pump was the problem, but once again could hear it running in the tank. Also, the system is holding fuel pressure good. It started right up this AM after sitting all night.
Conclusion: (any input more that welcome! I know 240's a lot better that 740's!) Suspect something going on with the in-tank pre-pump. It's either weak, intermittant, or both. With the full tank, the car has been fine for 2 days now. I'm running the main relay in my 240 just in case it may also be causing problems, but I really doubt it. All I can figure is that when the tank get under 3-4 gals I'm getting a fuel delivery problem and I'll need to have the pumps checked out (when I'm not broke!)
Hope this helps someone else sometime......
M
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