Cylinder #6 Misfire, only at ~6krpm

[DeathTrap]

Starting this thread with things that I've already replaced:
Spark Plugs
Coil Packs
Fuel Filter and hoses
VANOS seals
DISA O-ring

Seems to mostly happen in 3rd gear at around 6000 rpm. It's pretty repeatable and irritating as the DME cuts the cylinder out completely. I'm thinking it is a position sensor because of the exact place in the rpm range as well as the only cylinder that it happens to.

Edit: Also happens at part throttle at ~6k in third. I believe it is load independent. I'll have to be "that guy" and rev it in idle at see what happens.

Anyone have tips for an issue like this?

Freeze frame data from INPA:
https://farm5.staticflickr.com/4884/46082467881_00efce4033_c.jpg

[Sockethead]

Ryan (rkneeshaw) is having this same problem...he's a member here but here's his post on e46f
https://forum.e46fanatics.com/showthread.php?t=1242691

[DeathTrap]

Ahhh. Good to see someone much smarter than me already on the case. Seems like we have the same thought process, which is good.

I posted in his thread, might shoot him a PM as well. Thanks!

[rkneeshaw]

I dont know if I'd say "smarter", but we definitely seem to have the exact same issue, which makes me feel a little less crazy :)

I just shot you a PM. I haven't changed out my crankshaft sensor yet due to weather (car is hibernating in its cozy garage while it snows), but that is next on my list of things to try. Its also down to one of the only possible remaining things I can imagine could be causing this.

[dwonder]

Not 100% the same issue but when I accelerate hard, the car rocks/jerks (steering wheel has no vibration, new tires, alignment). This is all after I changed 6 coils/plugs. I had a SES light, which my indy shop says one of the cylinders said it was misfiring and if it happens again, he'll warranty it. Well, SES light came back. Do you guys think the jerking is due to misfiring? Only happens when I accelerate hard.

[rkneeshaw]

The crankshaft sensor didn't solve this issue for me. I also just replaced the headers and verified I have no exhaust leaks.

So now the list of things I've tried looks like this:


Swapped spark plugs and coil from cyl 6 to 1
Also replaced spark plugs with new plugs
Replaced cyl 6 fuel injector and inspected the electrical connector
Confirmed AFR of about 11:1 at the time of the misfire (suggesting the fuel system is keeping up fine since its not leaning out)
Removed the ESS manifold and pressure tested to ensure the intercooler wasn't leaking coolant into the cylinder, pressure tested good, held 11psi for over 4 hours. Resealed manifold to head, fresh gaskets, torqued to spec.
Compression tested: between 209 and 211 psi across all 6 cylinders
Free-rev to 6k RPM, held there, no misfires, it only happens under sustained load
Installed M3 motor mounts to match M3 trans mounts
Flashed known good tune to the car, still misfires
Replaced headers and installed all new hardware and gaskets, confirmed no exhaust leaks


This misfire problem only started after having the clutch and flywheel replaced. I've driven the car hard all summer and it wasn't an issue until that night on my way home from the shop after the clutch and flywheel install.

I feel like I've cleared every "real" source of a misfire (fuel is good, ignition is good, air is good), so I'm still thinking the problem has something to do with the detection of the misfire itself.

I mean, is it possible the new clutch and flywheel combo changed harmonics or something in just the right way that the DME thinks it detects a misfire?

I'm running a LUK OEM-style dual mass flywheel with a Sachs Performance clutch, and in case it matters I have an ATI super damper on the other end of the crank.

I've got a thread going on e46f for this issue too, cross-posting for posterity:

https://forum.e46fanatics.com/showthread.php?t=1242691

[racer2086]

Edit: just read your E46F post. 144k miles.

How about a leak down test?

Possible valve float going on at that high RPM due to a weak valve spring?

Very coincidental about the clutch replacement though. I'm with you on the thinking that maybe it's triggering a knock sensor or something, except that you should experience the same issue free revving at that RPM. Possibly, it is more related to the stiffer M3 mounts you used?

Deathtrap, did you do any clutch work before this problem started?

[cornercarver]

Given the coincidence of the misfire happening after the repair, I bet the tech who did the clutch/flywheel replacement unplugged something by accident or didn't properly re-plug a connector somewhere. Or maybe he took it for a joyride afterwards and broke something. Is he a mechanic you trust?

Funny story; (or not so funny, depending on your perspective) My buddy brought his truck to a shop for repairs, and on the way home he noticed it was running like crap. Next day he started it up and it ran fine. He also noticed his windshield washer fluid light was on. Turns out the mechanic re-connected a vaccum line to his washer fluid reservoir and the engine sucked it dry. Obviously not good for the motor...lucky he didn't blow a head gasket or something. I would have given the mechanic an earful.

[DeathTrap]

Edit: just read your E46F post. 144k miles.

How about a leak down test?

Possible valve float going on at that high RPM due to a weak valve spring?

Very coincidental about the clutch replacement though. I'm with you on the thinking that maybe it's triggering a knock sensor or something, except that you should experience the same issue free revving at that RPM. Possibly, it is more related to the stiffer M3 mounts you used?

Deathtrap, did you do any clutch work before this problem started?That's a negative. My car is bone stock, and the clutch was replaced many years ago according to the Carfax.

Luckily I have not had this issue reappear since I repaired my ECT sensor harness. Time for some back story...

FCPEuro had their New Year's sale and I decided to rack up on new parts. Fast forward to a few weeks ago, I removed my intake manifold to tackle all the things under there which includes:

Removing CCV
Replacing coolant pipes
Replacing coolant hoses
Starter
TB gasket
IM gasket
ECT sensor
Crank sensor
Both cam sensors

Whew. While the car was under the knife I noticed that my fuel injector clips were absent and someone ripped the ECT sensor harness and did a piss poor repair of it. Fixed those things, went to Road Atlanta and had a little hiccup. After that, haven't seen it yet.


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[racer2086]

Oh, so you solved your problem. And it was electrical related (or so you think) to that bad wiring repair. Interesting.

[rkneeshaw]

Unfortunately my issue has not been resolved yet.

I just tried replacing all coils with new, no change.

As a workaround for now, I used ByteTuner to change c_mis_max_nr_off_iv to 0 in the DME tune. This value controls how many cylinders are shut down when a misfire is detected. Default value is 2. I changed it to 0. I don't have cats, so no need to shut down cylinders if there's a misfire. Now when it does occur I get a single brief flash of the SES light, but otherwise I can't tell anything is going wrong, the car drives so good.

Updated list of things I've tried:

Replaced all 6 spark plugs with new
Replaced all 6 coils with new
Replaced cyl 6 fuel injector and inspected the electrical connector
Confirmed AFR of about 11:1 at the time of the misfire (suggesting the fuel system is keeping up fine since its not leaning out)
Removed the ESS manifold and pressure tested to ensure the intercooler wasn't leaking coolant into the cylinder, pressure tested good, held 11psi for over 4 hours. Resealed manifold to head, fresh gaskets, torqued to spec.
Compression tested: between 209 and 211 psi across all 6 cylinders (gauge is out of calibration, its probably 20-30 psi off)
Free-rev to 6k RPM, held there, no misfires. Also drove in 2nd gear and held RPMs at 6300 for a few seconds, no misfires. It only happens under sustained load such as in 3rd+ gear wide open throttle.
Installed M3 motor mounts to match M3 trans mounts
Flashed known good tune used on prior track days to the car, still misfires
Replaced headers and installed all new hardware and gaskets, confirmed no exhaust leaks


I'm starting to doubt some of my tests at this point, such as the pressure test I did on the ESS manifold. I applied 11psi to the inside of the intercooler circuit, which is the opposite direction of the pressure applied when the car is under full throttle. I should have applied vacuum to that circuit to better replicate the real world.

I guess the only other thing I could validate is the wiring harnesses. Ignition looks solid, and it routes in a place that wouldn't be effected by the clutch job, and its right on top, and everything looks super clean with no cracks in the sheathing etc. But the fueling wiring harness is harder to inspect due to it routing behind and below the huge ESS manifold.

Deathtrap, its interesting you repaired your ECT wiring, I wonder if an intermittent bad reading there would show up in some logs.

I'm going to run a fresh log on the car to validate fueling stays strong, which I believe it does, but can prove it now that the DME isn't shutting down cylinders when a misfire is detected. I'll log ECT too and see what that looks like.

It seems like these are the remaining possibilities at this point, probably in order of likelihood:

Intercooler coolant leak
Fueling wiring harness fault
Cam sensor failing intermittently? (seems highly unlikely or the symptoms would be different?)
Harmonics issue with the ATI damper, Sachs performance clutch, and OEM-style LUK dual mass flywheel (also seems highly unlikely)


I cant think of anything else that it could possibly be, anyone else have any thoughts on this?

[racer2086]

Man I was going to suggest all new coils.

Assuming everything else is good, what about a little extra carbon build up in that cylinder that is causing a hot spot, throwing the DME into a fit?

It sounds a lot like the 2800k rpm misfires I get only under load in 3rd+ gear. Revs fine in neutral, don't feel it in lower gears, and can't be explained other than a reflash that most people are doing, which supposedly loosens up the O2 tolerances. It seems BMW really squeezed what they could out of these cars mixture-wise.

For example, before I get to the point of flashing, I'm figuring something must have aged to get it the car to the level of having issues within a very restricted range. I was reading on one of the forums about how the DME at higher revs for the most part just runs off a set map, since it can't respond as quick to changes (no proof of this). If that is the case, this would lead me to think something mileage/age related has to do with the changes, and carbon build up could be one of those. I know some of these BMW engines can really carbon up over time. I'm running Marvel Mystery oil in my gas at the moment to see if anything improves. I cleared the adaptations before driving on a 400 mile round trip excursion. It ran much better. Started to come back, so then I added the MM. I thought I was crazy, but I surely notice a difference. Definitely not as bad and winds up quickly. I've had great luck with this stuff on my carb'd 85 Mustang, but I'm going to drive a lot more before I make a final call.

Have you done a leak down test in case there is a slight bit of loss out a valve or something? Could be slightly burned or a bit of carbon stuck in there causing a slight leak, which may or may not show up on a compression test.

Just my diagnostic thoughts, since you've pretty well covered things...

[rkneeshaw]

You know, I guess a leak down test is probably the only diagnostic test I haven't done yet. I dont think I'm geared up for it, I'll do some googling to see what equipment I would need to get it done.

[racer2086]

I got a quality OTC leak down tester off Amazon for around $60. Proved to me that the cold engine miss in my family's 90 Cadillac wasn't a mechanical issue. Almost zero leak down on the cylinder with the miss.

[DeathTrap]

Guess what decided to show up...

I guess I'm not done yet

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[rkneeshaw]

Aw dang.

I finally just used ByteTuner to update the DME so that it doesnt shut down cyl 6 when a misfire is detected. So now its just a flashing dash light when it happens. I can't tell anything is wrong other than the flashing dash light when it happens.

If you want to do the same, the parameter name is c_mis_max_nr_off_iv and you change it from 2 (default) to 0. This parameter controls the maximum number of cylinders the DME will shut down when a misfire is detected. Its intended to protect the catalytic converters. I run headers, so I'm not concerned with that.

I hate to have to resort to this, but I'm at my wits end, I really don't know what is causing this.

I do still plan to do a leak down test to see what that shows.

[DeathTrap]

Bump.

My misfire trigger RPM has decreased from ~6k, to around 4.5k.

Notes:
+ I have a seriously negative fuel trim at around idle and constant throttle

+ O2s and cats are still old

+ Rattling noise at lower rpm during rough running (i.e. when injector cuts out)

+Doesn't misfire when MAF is unplugged, MAF is new Siemens/VDO part.

I'll redo the standard diagnostics this weekend, maybe I can detect something this time.https://uploads.tapatalk-cdn.com/20191003/317d14e4a3e82748918a05311511d334.jpg

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[DeathTrap]

Fixed my fuel trims and MAF readings by tightening up the MAF pins, still didn't fix the misfire but I'll tighten up my other pins (coil, injector, DME) and see what happens. Compression is good, fuel pressure is good but couldn't check under a load...even if it was bad it would be a more global issue than cylinders specific.

Another thing is the misfire detection method that BMW has implemented is not 100%. Looking at the firing order for the straight 6, cylinder 3 fires before 6. Let's say, hypothetically, that cylinder 3 is the one misfiring. Then the misfire may get detected on the next "cycle."

Also, I am wayyyyyyy down on power. The car feels like a dog, I have to really push it just to keep up with even a 4 cyl Altima...this isn't fun.https://uploads.tapatalk-cdn.com/20191108/2c766fb56821d611d4400443e0995816.jpg

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[racer2086]

Deathtrap, since you're down so much on power, you could have clogged cats. Did you pull the O2s to release some pressure to see if it ran any better?

rkneeshaw, I realized that you had clutch work done when your issue started. I wonder if you have an exhaust leak from dropping the exhaust that is leaning out your O2s and causing the misfire.

There was another thread on here recently of someone having a higher RPM misfire in an engine after an engine swap. One bank was leaning out. It was fine before the swap. I suggested maybe a leak at the exhaust manifold letting oxygen into the exhaust and fooling the O2. Haven't heard back yet.

You can always smoke test the exhaust to look for leaks. That may also go for clogged cats, since if you don't get much flow out an O2 bung then somethings clogged.

Based on my 2800rpm stumble experience and the 4k dip, these engines seem extremely sensitive to O2 readings and knock sensor stuff. In my case, a DME update to the newest software solved all of those issues by loosening the O2 tolerances and clearing the knock adaptations. You guys may just have something slightly off causing the DME to freak out.

[DeathTrap]

Racer,

I believe I have clogged cats as well. My ZHP spits out a lot of soot sometimes. I had my wife rev the engine to 2000 rpms, I put my hand by the tail pipe and the amount and pressure of the exhaust was very weak.

2, I recall having a rattling noise upon cold start. Guess what? That noise is no longer present. That may have been the cat internals finally giving up and finding a nice resting spot in the exhaust.

Definitely time for headers....https://uploads.tapatalk-cdn.com/20191124/a8845356a66f2854930ab2682591a036.jpg

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[holyc0w]

I had a rattling noise too. After a few days, it settled and went away. Believe the cause was the same.

[DeathTrap]

Headers installed. The power is back and after a few pulls, no misfire. She's young again!

I'll run the car for a week, if the misfires do not return, we can consider this case solved.

[racer2086]

So exhaust leak?

[DeathTrap]

I would say so. That and/or a combo of clogged cats.

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[johnrando]

great news!

[DeathTrap]

She died on me today as I took her to redline in third. I was on the highway, airing it out, hit the rev limiter and got the same misfire code/symptoms as before. I'm thinking in my head that the problem isn't solved yet. I cycle the ignition on and off, but the problem doesn't go away. It has gotten worse. It feels like about 3 or 4 cylinders are completely out, very difficult to start due to the missing cylinders. I was able to limp it home and try to read codes, but I don't get anything but the cyl 6 misfire code.

I'm wondering if my timing jumped? Fuel is good, I *think* ignition is good. I need to do a compression test next...

[DeathTrap]

I found the root of this issue in the form of a broken keeper on cylinder #6https://uploads.tapatalk-cdn.com/20200116/b0a3c9c50bc1a08adcbe353f656380cc.jpg

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[ZHPizza]

Wait...so only one of the exhaust valves was opening on 6?

[DeathTrap]

It was probably opening fine...the closing part is questionable.

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[Will]

Damn, that's a bummer.

s54 swap?

[DeathTrap]

I wish! Lol
https://uploads.tapatalk-cdn.com/20200118/50c5f6591e0eac0ee226405c8ff74e14.jpg

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[Will]

Quick, here's an engine and transmission:

http://www.zhpmafia.com/forums/showthread.php?22582-Parting-Out-my-2005-330ci-ZHP

Edit: I didn't notice the initial posting date was Sept 2019. Sorry.

Edit 2: Just came across this on e46fanatics: parting out 125k miles, Beisan VANOS done. https://forum.e46fanatics.com/showthread.php?t=1269303

[DeathTrap]

I got a ZHP engine somewhat locally. I'll tear it down, inspect it, refresh it and slap it in. The original engine will be modified for more NA power... that's going to take a while lol.

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