High RPM Cylinder 6 Misfire

matt.ka24

New Member
Mar 28, 2021
3
0
0
Just bought this car a week ago. 229k Miles on it

Car is a 6AT, FBO with Pure600s

Getting a high RPM Cylinder 6 misfire. Car has fresh one step colder plugs gapped to .22, new coils, and a new, coded Index 12 injector on cyl 6. Car has a new crank sensor too. I should mention the car also surges while cruising with light load. Car will misfire above 6k and goes right back to normal after clearing the code. Baffled. Help.



 

nyt

Sergeant
Sep 15, 2019
332
1
291
0
Ride
2010 335xi
What are you running for fuel? Your trims are off between banks and you have massive corrections. Your high pressure fuel readings look good, but low is a little erratic.

Not sure if that's the cause of the misfire. It seems a ton of the 6at cars, particularly ije0s, show this trouble. Fresh coils, plugs, injectors, etc. Nothing cleared up my issue. Car was running on straight e85 with port injection. Anytime boost was about 20psi or above, there'd be a misfire above 6k rpm. I disabled misfire detection above 6krpm. Car ran great until I was doing some transmission tuning. Too fast shift and overboost bent the #3 rod. I was about to put my new setup in the car this weekend but had the wrong flex plate. I rebuilt the 6hp21 while I had it apart, and nothing looked amiss. Everything true, plenty of life left on the frictions, etc. Trans had 70k miles. I didn't cut the torque converter open to look at anything, though.

There are a bunch of misfire detection windows in the maps that may be able to be adjusted for this, but I don't think anyone aside from jyamona has mapped it, and we've been waiting for him to post a bunch of xdf updates for a long time.
 

SlowE93

Major
Jul 2, 2017
1,655
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Just a plane ticket away !
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E93
What are you running for fuel? Your trims are off between banks and you have massive corrections. Your high pressure fuel readings look good, but low is a little erratic.

Not sure if that's the cause of the misfire. It seems a ton of the 6at cars, particularly ije0s, show this trouble. Fresh coils, plugs, injectors, etc. Nothing cleared up my issue. Car was running on straight e85 with port injection. Anytime boost was about 20psi or above, there'd be a misfire above 6k rpm. I disabled misfire detection above 6krpm. Car ran great until I was doing some transmission tuning. Too fast shift and overboost bent the #3 rod. I was about to put my new setup in the car this weekend but had the wrong flex plate. I rebuilt the 6hp21 while I had it apart, and nothing looked amiss. Everything true, plenty of life left on the frictions, etc. Trans had 70k miles. I didn't cut the torque converter open to look at anything, though.

There are a bunch of misfire detection windows in the maps that may be able to be adjusted for this, but I don't think anyone aside from jyamona has mapped it, and we've been waiting for him to post a bunch of xdf updates for a long time.
What type of trans tuning ?
I know xHP has the sliders to increase shift speed. Using those or custom tuning making it shift much faster than that ?
 

matt.ka24

New Member
Mar 28, 2021
3
0
0
What are you running for fuel? Your trims are off between banks and you have massive corrections. Your high pressure fuel readings look good, but low is a little erratic.

Not sure if that's the cause of the misfire. It seems a ton of the 6at cars, particularly ije0s, show this trouble. Fresh coils, plugs, injectors, etc. Nothing cleared up my issue. Car was running on straight e85 with port injection. Anytime boost was about 20psi or above, there'd be a misfire above 6k rpm. I disabled misfire detection above 6krpm. Car ran great until I was doing some transmission tuning. Too fast shift and overboost bent the #3 rod. I was about to put my new setup in the car this weekend but had the wrong flex plate. I rebuilt the 6hp21 while I had it apart, and nothing looked amiss. Everything true, plenty of life left on the frictions, etc. Trans had 70k miles. I didn't cut the torque converter open to look at anything, though.

There are a bunch of misfire detection windows in the maps that may be able to be adjusted for this, but I don't think anyone aside from jyamona has mapped it, and we've been waiting for him to post a bunch of xdf updates for a long time.
Car is running 93oct. How are you going about disabling misfire detection? MHD doesn't seem to have this option for me. I'm guessing it would have to be something the tuner would have to do. After tearing the intake manifold off to look at the valves I decided to look at the injectors. Previous owner said he replaced the Index 12 injector in cylinder 6, but upon looking, cyl 6 is the only one with an index 12. Car has an Index 1 in Cyl 1, Index 11 in Cyl 2, Index 10 in 3 4 and 5, and 12 in 6. Would that be the cause of the trims being so wacky? What would cause these massive timing corrections?

What type of trans tuning ?
I know xHP has the sliders to increase shift speed. Using those or custom tuning making it shift much faster than that ?
Car has XHP stage 2 on it from previous owner. I have not messed with the trans tuning.
 

KClemente

Sergeant
Nov 26, 2019
291
149
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E90 335i
I know of some people that had their tuners turn off misfire detection over X rpm, but last I heard, Phuong (Doc Vu) solved one of my friend's 6 cyl misfire issue without turning off misf detection.
 
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matt.ka24

New Member
Mar 28, 2021
3
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0
I know of some people that had their tuners turn off misfire detection over X rpm, but last I heard, Phuong (Doc Vu) solved one of my friend's 6 cyl misfire issue without turning off misf detection.
Do you know the specifics of how?
 

KClemente

Sergeant
Nov 26, 2019
291
149
0
Ride
E90 335i
Do you know the specifics of how?
Nope but you could try messaging Doc Vu tuning on instagram or facebook and ask how to fix that misfire. I also know of another person that got a Rod Sutphin trans tune that quote on quote fixed it.

I don't talk to them much so I can't really tell you if it really fixed their misfires.
 

martymil

Major General
Sep 6, 2017
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Down Under
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S65 1m
looks like one of the injectors is leaking or more than one injector is not spraying properly stft's are too far apart.
 

sman217

Private
Oct 31, 2022
26
2
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I am curently having the exact same issue, car is going into fuel mode 15 over 6500 rpm and cyl 6 misfire. how did you fix this??
 

sman217

Private
Oct 31, 2022
26
2
0
nope, but nothing indicates its injectors, including my tuner. I have read this forum quite a bit and it seems to me like its a high HP issue on DCT and autpo cars. dct's dont like the DMFW, and the autos just shit the bed on big power over 6500 rpm. solution per tuner was upping timing a little and if that doesnt fix, going to turn off misfire detection
 

pbondar

Sergeant
May 30, 2020
439
253
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Interested in this as suffered from this issue too!

Have a new M2 DMF to fit this winter..
 

wheela

Captain
Jun 4, 2021
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2015 e84 X1 35i Msport
I'm wondering if this is due to crank twist, causing the power stroke from the piston to fall outside the allowable window for misfire detection? There must be some map for the misfire window? Here's what I posted over on 1addicts on @houtan thread:

As misfire is detected by the crank position sensor, I suspect there is some interaction between the motor and DCT at high power levels where crank twist causes the misfire detection to erroneously trip. I doubt the DME compensates for crank twist, so it seems plausible that as crank twist increases, there would be a point where the contributions from the various cylinders' power stroke would appear to not be happening at the correct time based on crank position (if the crank is twisting, then the end of the crank opposite the crank position sensor will be at a worst-case different rotational position than indicated by the crank position sensor - it would be further off the further you get from the crank position sensor). This is also why I suspect you can influence the problem by changing fly wheels - the different rotational inertia would influence the crank twist harmonics. I have no hard proof to back it up, this is just my theory.

@carabuser Have you come across any maps like this?
 

Jern54

Sergeant
Oct 18, 2019
295
1
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Netherlands
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E91 N54 335i
nope, but nothing indicates its injectors, including my tuner. I have read this forum quite a bit and it seems to me like its a high HP issue on DCT and autpo cars. dct's dont like the DMFW, and the autos just shit the bed on big power over 6500 rpm. solution per tuner was upping timing a little and if that doesnt fix, going to turn off misfire detection
Some time ago when I still had the 6HP I had the same issue. misfire at 6800 on cyl 6. It turned out to be a faulty injector.
At that time I was pushing 28PSI on chinesium 17T's
 

pbondar

Sergeant
May 30, 2020
439
253
0
I'm wondering if this is due to crank twist, causing the power stroke from the piston to fall outside the allowable window for misfire detection? There must be some map for the misfire window? Here's what I posted over on 1addicts on @houtan thread:

As misfire is detected by the crank position sensor, I suspect there is some interaction between the motor and DCT at high power levels where crank twist causes the misfire detection to erroneously trip. I doubt the DME compensates for crank twist, so it seems plausible that as crank twist increases, there would be a point where the contributions from the various cylinders' power stroke would appear to not be happening at the correct time based on crank position (if the crank is twisting, then the end of the crank opposite the crank position sensor will be at a worst-case different rotational position than indicated by the crank position sensor - it would be further off the further you get from the crank position sensor). This is also why I suspect you can influence the problem by changing fly wheels - the different rotational inertia would influence the crank twist harmonics. I have no hard proof to back it up, this is just my theory.

@carabuser Have you come across any maps like this?
Out of interest I wonder if there is a half that frequency effect which causes spurious timing knock corrections..I know it could be octane rating but seems strange that we have a lot of mid range timing corrections despite various attempts on variiis versions of tune at half the 6,500 ish frequency of the cyl 6 barfs..
 
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sman217

Private
Oct 31, 2022
26
2
0
Some time ago when I still had the 6HP I had the same issue. misfire at 6800 on cyl 6. It turned out to be a faulty injector.
At that time I was pushing 28PSI on chinesium 17T's
pi or di? my car doesnt show any signs of bad injector.
 

sman217

Private
Oct 31, 2022
26
2
0
if my car is on older tunes on lower boost it didnt have this problem. I can flash it it itll be fine.

it seems to be high hp only, and im not sure its relative to the injectors functionality because you also need to remember, my helix 3x had the same issue at same boost, and the di injectors were being taxed WAY more on that power. David and i have leaned heavily on Pi to test if it was a Di issue and the issue remained the same. 3rd gear doesnt seem to care about the issue (or lackthereof) and i can rev 3rd out to 6800-6900, 4th though doesnt play nicely over 6300 rpm.
I have a tune from david that disables misfire detection over 6000 rpm to see if that causes issue. if that doesnt fix it, and there is still active misfiring, i will absolutely lean on the side of actual misfire.