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Discussion Starter · #1 ·
I am helping a friend fix his 2013 850i. The engine turns when you turn the key but fails to start. The fuel pump is priming fine. After 6-10 tries, boom, it starts and idles just fine.

After that, if you turn it off; it will start immediately even if it has idled for just a few seconds.

At first my friend thought it might be the injector rail loosing pressure overnight but I am not convinced with the diagnosis. What could cause such a weird behavior? Battery is new, filters are new, fuel pump is new, fuses are fine and the starter has been rebuilt.

Any ideas? Are we missing something?
 

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Has fuel pressure actually been measured during this the no start and start condition or just assumed to be at correct fuel pressure.

During no start condition check for strong spark from all cylinders and measure fuel pressure.
Replicate when starting ok.

If just throwing parts at it, perhaps install a new fuel pump relay and fuel pressure regulator.

Good luck and pst back findings or resolution.
 

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Discussion Starter · #4 ·
Spark seems good at both cylinders. Fuel pump is new, but to my surprise I cranked it while holding a rag in the air intake in order to mimic a choke switch and now it only takes three or four cranks to get it to fire while it usually took around a dozen. Just like with a chainsaw, once you feel it coughs trying to start, I remove the rag and it fires up just fine.

This experiment lead me to think of the fuel pressure just like 200mph said, so the first suspect was a failing regulator. Placed a vice grip pinching the return line, cranked it but it made no real difference so my next step is to determine if the injectors are leaking fuel into the cylinder. That might explain why after the engine starts, subsequent starts are nornal.
 

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Discussion Starter · #5 ·
UPDATE: OK, finally it is fixed. It seems that the fuel system was not holding pressure. Took the thing apart and had the injectors cleaned with ultrasound and shop tested. Initially the were leaking and full of a black gunk that resembled tar. Also while at it took the regulator apart and removed the screen which was also clogged with the same gunk.

Now it is running like a champ and it fires right up at the first turn of the key.
 
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