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

Corporal
Sep 15, 2019
142
137
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

Lieutenant
Jul 2, 2017
721
268
0
Ride
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

Corporal
Nov 26, 2019
121
67
0
Ride
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
0
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

Corporal
Nov 26, 2019
121
67
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.