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      08-14-2019, 11:32 PM   #1
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Drives: 2007 335i coupe 6AT
Join Date: Nov 2013
Location: United States

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2009 BMW 750i single cylinder misfire issue N63 leaving me baffled.

first off let me say by saying I have a lot of experience with BMW's and I am just helpless with what normally is a simple bad ignition coil.

car: 2009 BMW 750i, well maintained with no smoke like they commonly do.

trouble code 140801 cylinder 8 misfire

Car starts up and idles perfectly smooth with no misfire all day long.

As soon as you go to drive it and accelerate it starts misfiring on cylinder 8 and throws malfunction light and then the dme shuts the fuel off to cylinder8 to save the cat.

shut the car off and start back up and misfire is gone and idles perfect. (until you accelerate)

the only fault code I get is cylinder 8 misfire injection cut out. None else.

I've replaced & tried:
New spark plug OEM on cylinder 8 (driver side bank closest to driver)
Used known good spark plug (gapped down as a test)
5x different ignition coils including 2 new ones and moving them around from that cylinder to another one.
2x series 12 fuel injectors.
Performed compression test = 160lbs or more
Replaced bank 2 HPFP with a known good one. (both banks read same fuel pressure)
Reset all engine DME adaptations and did injector balancing procedure.

Yet every time I go drive it I have misfire on #8 right when you get a little into the throttle and the turbos start to spool it cuts out.
Again, at idle I can not get it to misfire once. Period. Even if I power brake it to simulate a load on it.

What could possibly cause this or what would my next step be in the process of elimination?

Thank you very much and I hope this thread will resolve it and help the next poor soul having this frustrating problem.
Appreciate 0
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