Misfires log - need a guru!

[meddler]

I've been logging misfires over the last few months, out of interest more than anything else, and this is what it's thrown up.

Distance covered = 3,000 miles
Car = BMW 325i Touring (N53 straight-six 3.0 petrol)
Source = Bimmerlink, change in total misfires over time (ie the last 3,000 miles)

Cylinder 1, + 25
Cylinder 2, +76
Cylinder 3, +27
Cylinder 4, +119
Cylinder 5, +424
Cylinder 6, +60

Are there any misfire gurus out there who can tell me whether this looks normal or abnormal? Particularly Cylinder 5. Ta v much!

[Panamax]

Presumably you have no Check Engine Light illuminated but have you checked for codes?

[GreenV8S]

It's perfectly normal to get occasional isolated misfires without any underlying fault. The rate you'rfe seeing is consistent with that.

There are also faults which can provoke misfires, and the ECU can detect some of them. If you see fault codes, it's worth following up what they're warning you about. But a low rate of misfires like you're seeing without any accompanying fault codes is safe to ignore.

[meddler]

Thanks both.

No CEL, no misfire codes.

Do you know of any reason why Cylinder 5 misfires are so much higher than the others?

[GreenV8S]

meddler said:

Do you know of any reason why Cylinder 5 misfires are so much higher than the others?

There are millions of differences between cylinders that usually don't have any significant impact but could be enough to make individual cylinders slightly more susceptible to misfires under specific conditions.

[Panamax]

No codes = no problems.

Routine misfires as per GreenV8S above. I certainly wouldn't start replacing components on the off-chance. If it ain't broke, don't fix it. If you're bothered you could swap some of your existing parts between cylinders to see if it made any difference going forwards.

[jeremyc]

You need to put the data into perspective. If we assume that you've averaged 30mph and 3,000rpm over those 3,000 miles then even your 424 misfires on cylinder 5 represent, on average:

• a single misfire every 7 miles or 14 minutes of driving.
• a misfire every 0.028% of firing opportunities.

Assuming my maths are correct, of course.

[meddler]

Thanks all for the advice. And I’m sure that maths is good

[Krikkit]

If you want to try something swap the coilpack from cylinder 5 to another and see if it moves. But as above I wouldn't worry about that kind of misfire tally at all, only once you get an EML or start to feel it misfiring would I start investigating.

[meddler]

Krikkit said:

If you want to try something swap the coilpack from cylinder 5 to another and see if it moves. But as above I wouldn't worry about that kind of misfire tally at all, only once you get an EML or start to feel it misfiring would I start investigating.

Yeah, that was my thinking. Wouldn’t need to swap plugs because I put in new ones 4,000 miles ago (and the old ones were in remarkably good shape when I took them out). And given I’m not detecting any misfires while driving, I’ll leave it for now.