Mystery Misfire

Cheezy

Lieutenant
Nov 7, 2016
610
223
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Toledo Ohio
Alright guys, i need some help. I have a high rpm misfire only in cyl6.
About the car
08 335xi 6at
Dci, chargepipe, vrsf 7" hd fmic, muffler delete, fuel it stg2 bucketless lpfp, mhd v5 e40, xHP Stg2 trans flash.
Misfires only occur after 6300 rpm in 3rd gear or 6100 in 4th gear. Only in cyl6 with no ther codes at all. . Ive recently had the intake valves walnut blasted about 5000mi ago. i changed the plugs to ngk gapped at .020, coil packs were done at the same time as walnut blast, and i did swap out cyl6 plug and coil to see if they were faulty, nothing changed. So i had the injectors replaced with new index 12. Still have a misfire. Logs show fuel rail staying above 2000psi so i dont think the hpfp is faulty. The dme is msd80 so theres a possibility of the mosfet going, but i feel like it would be all the time. I also thought maybe exhaust restriction like a clogged cat but that would mess with the whole bank. And wouldnt a bent or stuck valve give more issues at all rpm ranges?. I have bl tuning coils on the way and thats really my last attempt at a fix. When i reset all adaptations it clears up for about 10 pulls then comes back. I havent had the time to go through and reset them one by one to see which one solves it, but that would be my next plan. Ive read other threads similar to this but it was for a mt car and his issue ended up being dmfw. If any of you experts have had a similar issue and can give a pointer on what solved your issue, let me know. Any suggestions that lead to a solution will be greatly appreciated!!
 

The Convert

Captain
Jun 4, 2017
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Do you have any logs showing the misfire? Have you done a leak down or compression check? Iirc, there have been some people with broken ringlands or cracked pistons end up having an "unsolvable" misfire that leads them to discover the internal damage.

Obviously hope this isn't the case for you. Definitely a head scratcher.
 

Cheezy

Lieutenant
Nov 7, 2016
610
223
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Toledo Ohio
I actually do have a log from the first time i had it. I was on mhd v7 e60. When i had the injectors done i asked to have a compression test done but he forgot. I told him before i tested it if the problem persists id bring it back for the comp test. If it were ringlands wouldnt i be burning oil or smoking at least a little? I just dont understand how a mechanical issue would only be after a certain rpm range.
 

Bmwfixerguy1

Lieutenant
Jun 5, 2017
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07 335i MT
Sometimes ring lands or internal like stated above. Also tuning can play a.huge part as well like if this is happening at a shift which it might be could be tuning.
You have to have a compression and leak down done if you have done all the other normals. If resetting adaptations does it that makes it sound fuel related bit doesn't have to be. Your just retting the "trims" to less likely to miss senario

I'm curious to see if could solves the problem.

Keep us posted and if I can think of anything I'll post it
 

Cheezy

Lieutenant
Nov 7, 2016
610
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Toledo Ohio
I filled up with 93 and flashed back to mhd stg1+ . So far its solved my misfire issue. Its also weak as fuck. I hate it. So im gonna say fuel delivery problem or catted downpipe restriction. But it might just be so less agressive that its not triggering the issue. For example this tune only hits about 16psi then tapers to 14, where my problem always occured after it tapered off to over 17.5psi. I need to take my car to bmw for airbag recall, ill see if i can talk them into replacing my hpfp under their 120k warranty. Ill make sure im flashed to stock and have fuel pump codes present.
 

Cheezy

Lieutenant
Nov 7, 2016
610
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Toledo Ohio
Alright so i did a tremendous amount of studying my own logs and other peoples, comparing my numbers to whats been recieved as acceptable. My stft's were maxing out -34. My afrs were also dipping pretty rich. Like high 10s. So i can only assume my plug gap was too small to get a complete burn in the combustion. Maybe the Dme was seeing rich afrs and trying to pull fuel to level it out, and since cyl6 was the farthest away from the pumps it saw the lowest pressure and just cut off??? Anyway i installed the BimmerlifeTuning coil kit and opened the plug gaps to .026in. Fueled with e60, checked the bl coil box on mhd and tuned mhd v7 e60. Ive done several pulls with no issues so far. Im heading to the track tomorrow to see if this solution is the real deal or not. I hope that it is.
 

V8bait

Sergeant
Nov 2, 2016
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Texas
You need to fix the issue with the trims going full negative, these motors don't like it that rich and it can throw you into open loop which would lead to very lean condition.
 

Cheezy

Lieutenant
Nov 7, 2016
610
223
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Toledo Ohio
You need to fix the issue with the trims going full negative, these motors don't like it that rich and it can throw you into open loop which would lead to very lean condition.
Yeah i figured that much but im not a tuner and dont want to get a custom tune yet. So i added the coils to help burn more fuel. I went to the track and took some logs. Afrs never got below 12.0 (except mid shift so does thst really count?) And stfts stayed less than -20 at peak rpm. Track conditions were shit. There were 150 cars there so i only got to make 2 passes in 4 hours. No misfires. Second pass was against a tuned '16 f10 m5. I watched him do 12.5 so i was like Yeah ill line up with you. He went 11.66 and i went 12.02. Not really proud because ive done better, conditions just werent there. Cars done for the year. Dps, inlets, and port injection are going on soon then a real tune haha. Try again next year. As a conclusion tho i think the BimmerlifeTuning coil kit solved the misfire issue.
 

V8bait

Sergeant
Nov 2, 2016
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Yeah i figured that much but im not a tuner and dont want to get a custom tune yet. So i added the coils to help burn more fuel. I went to the track and took some logs. Afrs never got below 12.0 (except mid shift so does thst really count?) And stfts stayed less than -20 at peak rpm. Track conditions were shit. There were 150 cars there so i only got to make 2 passes in 4 hours. No misfires. Second pass was against a tuned '16 f10 m5. I watched him do 12.5 so i was like Yeah ill line up with you. He went 11.66 and i went 12.02. Not really proud because ive done better, conditions just werent there. Cars done for the year. Dps, inlets, and port injection are going on soon then a real tune haha. Try again next year. As a conclusion tho i think the BimmerlifeTuning coil kit solved the misfire issue.

Your fuel trims not being full negative with rich afr solved your misfire issue. Coils def didn't hurt, though. Upgraded coils can ignite worse mixtures to a point, I'd still get the tune adjusted.
 

Bmwfixerguy1

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Jun 5, 2017
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Your fuel trims not being full negative with rich afr solved your misfire issue. Coils def didn't hurt, though. Upgraded coils can ignite worse mixtures to a point, I'd still get the tune adjusted.


It was more like a cast not a band aid
 

fmorelli

Major General
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Aug 11, 2017
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I'd suggest resetting all fuel-related adaptations, and then see what happens. I was having similar issues (after having replaced plugs, coils) along with some oddball 02 sensor errors (even post-cat stuff I've never seen on a car). I'm 400+ miles in with no CEL since resetting adaptations. Easy to do, can't hurt, doesn't cost anything.

Filippo
 

Cheezy

Lieutenant
Nov 7, 2016
610
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Toledo Ohio
I'd suggest resetting all fuel-related adaptations, and then see what happens. I was having similar issues (after having replaced plugs, coils) along with some oddball 02 sensor errors (even post-cat stuff I've never seen on a car). I'm 400+ miles in with no CEL since resetting adaptations. Easy to do, can't hurt, doesn't cost anything.

Filippo
When i was having this issue i did reset the adaptation values, it would work for about 30 miles then the issue would come back. Since upgrading coils i havent had the issue, also with the v8 beta maps i havent had any issues.
 

Cheezy

Lieutenant
Nov 7, 2016
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Toledo Ohio
I'm going to update this incase some poor soul down the road encounters this issue.

The misfire decided to show it's ugly face again today. This all comes after changing injectors, coils, plugs, knock sensors, crank position sensors, turbos, torque converter, transmission, engine mounts, transfer case mount. I've installed a PI kit. Running full e85. Fresh walnut blast right before that kit went on about 1k ago. I have custom tuning.

In the past we concluded that it was false misfire and turned off misfire detection over 6200rpm. Before it would only occur in a multi gear pull (like a launch up to 3rd), in third gear, 21psi minimum, and almost exactly at 6300rpm. Now it seems to be happening at 5000rpm almost like clockwork. I have 3 logs from a dig showing the same thing. if it is just chatter setting off misfire detection, I would like to know what the heck is chattering. I'm going to do a compression check and borescope that cylinder to check for obvious damage. I'm also waiting on the AC fab pcv fitting so I can delete my flapper valve and run a check valve setup. Maybe crankcase pressure is my issue?
Does anyone have any other ideas?
 

V8bait

Sergeant
Nov 2, 2016
495
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Texas
Cracked valve covers/gaskets and bad pcv stuff can cause odd things to happen sometimes... I think that's a good direction to go at this point in your story.
 

Cheezy

Lieutenant
Nov 7, 2016
610
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Toledo Ohio
@V8bait those were my next steps. Eventually I'll find the issue. My ac fab fitting came in, so I ran a check valve to delete the OEM flapper, with a small section of hose to the inlet thus deleting my catch can. I wanted to eliminate any impedance of flow. When I pulled the plugs to check compression there was no oil so I assume that the vcg is fine, and the VC itself looks good, but I'm going to get a whole kit from FCP to replace it. I used a cheap harbor freight compression tester and I'm suspicious that it was inaccurate. It gave me readings between 120-125psi across all cylinders, wet and dry. So im going to find a quality compression tester that's proven accurate and retest. These are the next steps.
 

Jeffman

Captain
Jan 7, 2017
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I had a misfire in cylinder 2 the other week. Thought it was my PR coil but first checked the plug. Well surprise, surprise! The damn plug was loose despite carefully torquing it to spec (23 NM). Replaced it with a new NGK 95770 plug gapped to 0.022 and all is good.
 

fmorelli

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Aug 11, 2017
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I had a misfire in cylinder 2 the other week. Thought it was my PR coil but first checked the plug. Well surprise, surprise! The damn plug was loose despite carefully torquing it to spec (23 NM). Replaced it with a new NGK 95770 plug gapped to 0.022 and all is good.
Were they new plugs you installed? Had they be put in for the first time or reinstalled? And ... which plugs were they?

Filippo
 

Jeffman

Captain
Jan 7, 2017
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Were they new plugs you installed? Had they be put in for the first time or reinstalled? And ... which plugs were they?

Filippo
Yep - all new NGK 95770 plugs gapped to .022 inch installed with the PR coils 1400 miles back in October. All torqued down to 23 NM (so I thought!). Noticed the old one’s crush washer was indeed crushed when I took it out. So I can only assume it really wasn’t properly torqued down. Perhaps something got caught in the threads. I recall having removed somewhat loose plugs in the past. So I’ll be retorqueing them in a few months.
 

Cheezy

Lieutenant
Nov 7, 2016
610
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Toledo Ohio
Yep - all new NGK 95770 plugs gapped to .022 inch installed with the PR coils 1400 miles back in October. All torqued down to 23 NM (so I thought!). Noticed the old one’s crush washer was indeed crushed when I took it out. So I can only assume it really wasn’t properly torqued down. Perhaps something got caught in the threads. I recall having removed somewhat loose plugs in the past. So I’ll be retorqueing them in a few months.

I've noticed that issue in the past, but it's not the cause of this misfire. To be honest, when I pulled the plugs to check compression, they were all only finger tight, and I've used a torque wrench everytime I've ever installed plugs. I even found that one of my plugs electrode insulator was broken, but there was no problems in that cylinder either! Crazy engines.