[NewM235Owner]

E93 2007 104,000 Auto.

Car drives fine for 30-40 minutes, can run it up 6500 RPMs, everything seems fine. After the 30-40 minute mark, I get a CEL, car is running rough, and the CEL is always cylinder misfire 4.

I have new index 12 FIs, new spark plugs, not new coils but I've swapped everything around several times, plugs, coils, FIs, and it's always cylinder 4 after the engine has been running for 30 -40+ minutes.

Any ideas on what to try next?

Thanks

[N54_e90]

Compression and leak down test

[NewM235Owner]

OK, thanks for those ideas, they are pushing my knowledge/experience a little but that's good - I'll give those a shot.

My son is convinced it needs a walnut blasting, and it probably does since it's never been done, but I don't think the carbon buildup would cause the same cylinder to misfire each time.

[Dave92N54]

Originally Posted by NewM235Owner

OK, thanks for those ideas, they are pushing my knowledge/experience a little but that's good - I'll give those a shot.

My son is convinced it needs a walnut blasting, and it probably does since it's never been done, but I don't think the carbon buildup would cause the same cylinder to misfire each time.

I believe it can but my understanding is cyl 4 on these cars sees the most wear typically. Start with a comp test, for the most part ignore the actual values and focus on variation between cylinders. If 4 is off, do a leak down. If comp values are all relatively close to each other, i'd go with a walnut blast.

[Saif2018]

Originally Posted by NewM235Owner

OK, thanks for those ideas, they are pushing my knowledge/experience a little but that's good - I'll give those a shot.

My son is convinced it needs a walnut blasting, and it probably does since it's never been done, but I don't think the carbon buildup would cause the same cylinder to misfire each time.

Carbon build up can cause misfires though, good idea to walnut blast anyway.

[whyzee125]

Carbón buildup Can definitely cause that. If it’s never been done I’d start there

[georgewny]

Originally Posted by NewM235Owner

OK, thanks for those ideas, they are pushing my knowledge/experience a little but that's good - I'll give those a shot.

My son is convinced it needs a walnut blasting, and it probably does since it's never been done, but I don't think the carbon buildup would cause the same cylinder to misfire each time.

NewM235Owner
You might want to watch this video on Youtube from user " Vehicular DIY " .
He is quite knowledgeable on the BMW's and especially N54 M's

Check out this:

It is a slightly different issue then what you are experiencing, but he talks about issues that could be caused from a FI port that may not be perfectly round. Also at 5 minutes in, check out how he applies high temperature Teflon tape (strange but true!)

it quite the informative meeting.

Good luck.