M52B28 No fuel when engine is at temp, starts up normally once and after cooling down

[n4ppy]

I've been struggling with an ongoing issue with my m52b28 swapped e30 for a awhile now and I would appreciate any input you guys have to offer.

The vehicle is able to consistently start without any trouble as long as the engine is cold. It never dies during that initial driving session but as soon as I turn the vehicle off and attempt to start it back up it just endlessly cranks.

The engine is running rich and I can smell unburnt fuel both while driving and after I park it. There is spark during it's failure to start. Spraying starting into the throttle body does not change its condition. I have a brand new fuel pump and it is priming appropriately. I am running the e39 m52 fuel rail with the built in FPR. I tried another FPR on this same fuel rail as well.

If I leave the car alone to come back down in temperature it will start as normal. This generally takes somewhere around 2 hours to occur. It seems like it almost must be a vapor lock condition but I'm unsure how to move forward.

Please, I'm hitting my head against the wall. If there's anyone that can provide me with some insight I would greatly appreciate it.

[318ti808]

Have u changed your fuel filter? Had similar vapor lock symptoms in my e30 30 or so years ago. I think that was my solution.

Try google symptoms of bmw dirty or clogged fuel filter


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[n4ppy]

I have not replaced the fuel filter but I have one ready to install. I'll do so shortly and report back. Thanks!

[318ti808]

Although u mentioned u swapped out your fuel pressure regulator, if it was not with a new one I would test your fuel pressure at the fuel rail to make sure u have pressure within the spec range. It could be another pressure regulator going bad. I also recall replacing the pressure regulator, which might have been at the time I had the vapor lock problem/symptoms.


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[TobyB]

If you're sure there's spark, that rules out a lot of things.
Annoyingly, not running on starting fluid rules out most of the others...

I agree, measure fuel pressure at the rail.

Next, you're looking for a heat soak problem-
the crank sensor's a prime candidate, but if you're getting
spark, it's probably not that. Is it an OBD2 DME?
If so, have a listen to it and see if it's getting rev data
when cranking, and what the DME's doing in response.

erf.

t

[Northern]

^ +1 to this, worth a shot to look through INPA or some sort of code reader that shows live data, and see if there is any sensor that seems to be spitting out garbage.