Cyl 6 misfire

N54gasm

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Feb 6, 2017
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New Freedom
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In the process of tuning the new turbos but this problem also goes back a little while. It's always cyl 6 that misfires. Car has new ngk plugs gapped at.018, new index 12 injector (all inj are index 12, replaced this one cuz figured I got a faulty inj), precision race works ignition coils. Car has all maintenance done (walnut blast done 22k miles ago). Tuner says it's not tune related. Fuel is fine, ignition etc. The misfire also isn't constant. Could be my next pull, 5 after that, etc but always the same cyl.

Attached is a log that the misfire happens. Next step is to compression test and prob switch the pr coil to another cyl and see if it follows.
 

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  • 2018-09-04 12_17_54.csv
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P33P33

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Apr 3, 2017
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BMW 335i n54 e93
I had that same issue for a long time. PR coils helped a bit and taking ignition timing down. Eventually I swapped number 1 and 6 injectors and that solved the problem. What I found out was that the number 6 injector o-ring was showing some signs of leakage upwards from cylinder.
 

N54gasm

Corporal
Feb 6, 2017
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New Freedom
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I would def swap coil before going further

Waiting on the car to cool down and ima go for another few pulls.

I had that same issue for a long time. PR coils helped a bit and taking ignition timing down. Eventually I swapped number 1 and 6 injectors and that solved the problem. What I found out was that the number 6 injector o-ring was showing some signs of leakage upwards from cylinder.

It's a brand new Injector.
 

Jeffman

Captain
Jan 7, 2017
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I’d double check to make sure Cyl 6 intake was actually properly cleaned when walnut blasted. Did you do it yourself and check to see both intake valves were thoroughly cleaned?

Cyl6 intake is the hardest one to get really clean since it’s right up against the fire wall and getting the blaster wand at the correct angle to thoroughly clean both valves was a PITA when I cleaned mine in July. I actually needed to put an extra bend in the blaster wand to get to the left valve.
 

NoQuarter

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Nov 24, 2017
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Cyl6 intake is the hardest one to get really clean since it’s right up against the fire wall

Yep. And my stoopid a$$ continues to do them left to right. When I am tired of the whole process is when I get to number 6.
"Do them right to left!" I need to remind myself next time.
 
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marc

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Aug 26, 2017
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what flywheel does the car have? if it's the DMFW then this might be causing the misfire. i had a similar issue, replaced my DMFW with a SMFW and no more misfire.
 

NoQuarter

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what flywheel does the car have? if it's the DMFW then this might be causing the misfire. i had a similar issue, replaced my DMFW with a SMFW and no more misfire.

Isn't this the exact opposite of what happens? The SMFW causes more misfire issues and has to be accounted for?
 
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marc

New Member
Aug 26, 2017
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Isn't this the exact opposite of what happens? The SMFW causes more misfire issues and has to be accounted for?
not really, no. at high loads high rpm the DMFW vibrates, which in terms will trick the DME/ knock sensor to pick up false knock on cyl 6 since it's the closest to the flywheel, hence the DME will shut off cyl 6 resulting in a misfire.
 
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NoQuarter

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not really, no. at high loads high rpm the DMFW vibrates, which in terms will trick the DME/ knock sensor to pick up false knock on cyl 6 since it's the closest to the flywheel, hence the DME will shut off cyl 6 resulting in a misfire.

So the SMFW vibrates more (in general) than the DMFW, just not so much that it causes the false misfire at high RPM?
This is something I want to read up on some more.
 

langsbr

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Apr 5, 2017
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So the SMFW vibrates more (in general) than the DMFW, just not so much that it causes the false misfire at high RPM?
This is something I want to read up on some more.

I think it might be better phrased as "at idle, the SMFW doesn't dampen vibrations like the DMFW does." At WOT, the DMFW attempts to dampen vibration are misinterpreted as misfires or knock."
 
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N54gasm

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Feb 6, 2017
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Car is an auto. And all intake valves are pretty good (some build up but no more or less than the other cylinders).

Also, am replacing the injectors on the PI (larger) as I was maxing the others out and changing gaskets in the meantime.

Compression test is good, and leakdown is good.
 

Rcboosted2007

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Jan 28, 2018
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07 335i
Car is an auto. And all intake valves are pretty good (some build up but no more or less than the other cylinders).

Also, am replacing the injectors on the PI (larger) as I was maxing the others out and changing gaskets in the meantime.

Compression test is good, and leakdown is good.
Great news! Glad to hear its not a costly issue.
 

N54gasm

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Feb 6, 2017
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New Freedom
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Honestly, havnt tried. Tired of spending $75 for plugs lol. Replaced them 3 times within 8k miles, thinking maybe it was them. And I have a thing where I cant replace just one, gotta do them all lol. Currently NGK 95770 Even swapped the same plug to another cyl, still the same 6 cyl misfire.

I havnt tested mosfets, but being my dme is a msd81 I want to say its not them.

Figure ill test the connection/wire to the coil tomorrow. Maybe see how the tuner will like maybe doing something tune related like desensitize or disable misfire detection for a log or so (after we make sure fueling and timing is set) to see if I can feel or see anything in the log (I want to say its false knock) maybe by too much chatter of something rubbing, etc.
 
Last edited:

Rcboosted2007

Lieutenant
Jan 28, 2018
902
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Parts unknown
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07 335i
Honestly, havnt tried. Tired of spending $75 for plugs lol. Replaced them 3 times within 8k miles, thinking maybe it was them. And I have a thing where I cant replace just one, gotta do them all lol. Currently NGK 95770 Even swapped the same plug to another cyl, still the same 6 cyl misfire.

I havnt tested mosfets, but being my dme is a msd81 I want to say its not them.

Figure ill test the connection/wire to the coil tomorrow. Maybe see how the tuner will like maybe doing something tune related like desensitize or disable misfire detection for a log or so (after we make sure fueling and timing is set) to see if I can feel or see anything in the log (I want to say its false knock) maybe by too much chatter of something rubbing, etc.
Bro i just found out that fcp euro(who i bought injectors from) offers free lifetime replacement of all parts they sale. Including brakes,spark plugs, windshield wipers. Literally everything lol.
 
Jan 31, 2017
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www.hydraperformance.com
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2010 135i 6MT
At the risk of sounding silly, but what's the big deal about disabling misfire detection on a higher powered N54, especially since it appears to be a common issue on this platform as boost is increased. It could just be an artifact of unequal cyl filling, pumping losses, or even crankshaft deflection @ higher cyl pressures being picked up as misfires. Many other platforms do just fine without this additional safety nanny, so unless the misfire detection thresholds can be found and modified, why bother with them?