Bank 1 Misfires - Multiple misfire codes, low combustion quality bank 1

[tdott]

In the mist of troubleshooting a bank 1 misfire issue that is getting interesting...

Codes:
2B35 DME: Misfire with cutoff, cyl. 1
2B36 DME: Misfire with cutoff, cyl. 2
2B37 DME: Misfire with cutoff, cyl. 3
2B38 DME: Misfire with cutoff, cyl. 4
2B41 DME: Misfire with cutout, several cylinders

Most recent work and driving history:
- AA high flow cats removed, AA Test pipes installed to AA mid-pipe (currently catless)
- New donut gaskets installed
- Ran without a CEL for 3 weeks, attended a track event, 1 week after the track event CEL popped up

Things checked so far:
- Exhaust leaks, no leak at header/xpipe connection, or AA test pipe V Band.
- Engine grounds (none were recently touched)
- ISTA misfire dedection
- After codes are cleared, and restarted, after about 2-3 minutes of idle, it will throw the codes above and go into cylinder deactivation mode and randomly shut down 1 cyl. (not always the same cyl)
- Confirm both TAs are opening and closing smoothly.
- Swapped coils bank to bank
- Swapped Pre-cat o2 sensors, side to side.
- Installed new OEM spark plugs
- Installed new low pressure fuel sensor
- Smoke tested Bank 1 header for leaks

ISTA misfire detection chart from cold start, screencapture:


Bank 1 (Cyl 1-4) combustion quality is consistently lower than Bank 2. Bank 1 is bearly above 0, and Bank 2 is closer to 1. Bank 1 has random misfires, you'll see a certin points above cyl 1, 2, 3 go to 0. But all 1-4 have misfires at certain points.

Plan of attack
- Take the plenum off, check to make sure the butterflies are moving freely and opening
- Not sure yet, might swap pre-cat o2 sensors to see if that changes anything.
- Might swap coils bank to bank


Open to ideas, will update as I rule out certain things, but haven't encountered this one before, so let me know if anyone has any suggestions.

[spammysammich]

when you check coils and plugs on that bank, maybe throw in a compression/leakdown test on cyl 1?

[tdott]

Originally Posted by spammysammich

when you check coils and plugs on that bank, maybe throw in a compression/leakdown test on cyl 1?

It seems to pick a random cyl to shut down after a few mins of idling, while logging combustion quality 3 different times without changing anything, it shut down cyl 1, then 3 the next time, then 2 the next.

I don't think there is anything specific to cyl 1 yet, but I did pull a plug to make sure I didn't smell it full of fuel.

I don't think it's a bad coil, the full bank normally wouldn't go together, or a bad plug. Plugs I pulled looks good. But I may swap coils bank to bank if I don't have a better idea tomorrow.

[amrazM]

is it misfiring above 2500RPM?

[charliev68]

It might be a valve spring. You are naming all the symptoms

[tdott]

My current theory is a exhaust leak at the head / header connection on Bank 1.

I ordered a smoke detector to hopefully confirm this.

Originally Posted by amrazM

is it misfiring above 2500RPM?

No, doesn't appear to be, I held the RPM steady until it warmed up and it wasn't misfiring above idle. Once warmed up misfires were reduced, but still the odd misfire at idle. Once warmed up, it didn't shut down any cylinders or throw a CEL for the time I had it running, which it usually would have already when idling from cold.

Originally Posted by charliev68

It might be a valve spring. You are naming all the symptoms

I would expect the misfire to be isolated to the broken valve spring cylinder no? But yes, haven't completely ruled that out yet.


I noticed a difference in exhaust temps after I had held the rpms around 2500 until it warmed up.
The o2 sensor test won't complete because of this.

[tdott]

Additional things checked, but issue is still the same.
- New Plugs
- Coils swapped bank to bank
- TAs checked, moving freely and testing fine.
- New updated Low pressure fuel sensor installed.

[omgzirra_exe]

Originally Posted by tdott

My currently theory is a exhaust leak at the head / header connection on Bank 1.

I've been dealing with the same single bank misfire issue for months. It doesn't happen while idling; rather, it occurs when I go wide open throttle (WOT) in 7th gear at 3k rpm. The engine starts to bog and stutter.

It could be an ignition issue on my end or an air-fuel ratio problem caused by an exhaust leak somewhere, possibly at my headers.

According to BMW Tools, my bank 2 vanos is slightly off compared to my bank 1 vanos. I'll need to clean and swap those and see what happens.

[yardbro]

Interesting. Definitely going to want to see the results once you get that smoke tester to be absolutely positive there isn't an exhaust leak going on here. After you clear codes have you checked lambda on the O2 sensors before it goes into cylinder deactivation? If you have a steady miss these readings will probably be skewed anyway, but worth taking a look as these are things you can do while you wait on your tool.

In the meantime, are you able to do a compression test on the cylinders in that bank just to be more certain there isn't a mechanical issue at play here?

[tdott]

Originally Posted by yardbro

Interesting. Definitely going to want to see the results once you get that smoke tester to be absolutely positive there isn't an exhaust leak going on here. After you clear codes have you checked lambda on the O2 sensors before it goes into cylinder deactivation?

Yes I was looking at the live readings in INPA, the voltages are the same on each bank when I hold the trottle steady above idle, but when I let it idle and misfire I see the bank 1 voltage differ.

I tried to run the o2 sensor test in ISTA but because it detects the egt on each side being different, it doesn't start the test as shown in the above screenshot.

I also did swap pre-cat o2 sensors bank to bank.

Originally Posted by yardbro

In the meantime, are you able to do a compression test on the cylinders in that bank just to be more certain there isn't a mechanical issue at play here?

I don't have compression test tools unfortunately, I could go borrow one but I feel like low compression should throw a consisent misfire in the effected cylinders. Perhaps if the smoke test doesn't point to a leak, then i'll have to.

Thanks for the suggestions.

[tdott]

Originally Posted by omgzirra_exe

It could be an ignition issue on my end or an air-fuel ratio problem caused by an exhaust leak somewhere, possibly at my headers.

According to BMW Tools, my bank 2 vanos is slightly off compared to my bank 1 vanos. I'll need to clean and swap those and see what happens.

Yea high rpm misfires sound more like an igition issue, perhaps a weak coil.

For vanos you could try running the vanos test in ISTA to see if it passes, if you are seeing a difference you aren't sure about.

[omgzirra_exe]

Originally Posted by tdott

Yea high rpm misfires sound more like an igition issue, perhaps a weak coil.

For vanos you could try running the vanos test in ISTA to see if it passes, if you are seeing a difference you aren't sure about.

Quite possibly, but I did swap them around recently, and no codes followed or changed. (Also, I sort of don't want to spend $240 for it right now since nothing significant changed.) I'll check with a multimeter.

I'll probably just do a spark plug job since I'm at that point now and make sure they are torqued properly.

I'll do the Vanos test this weekend and see what happens.

[tdott]

Smoke test didn't lead to anything conclusive.

It's holding the 19psi the machine is putting out and no smoke is coming out.

Unless the leak only is under high back pressure, I'm not sure if it's the header gasket.


Compression test, leak down test and ruling out a broken valve spring sounds like next steps....

[MineralWhiteF80]

after reading your progress, my mind immediately asks, "What components or systems are responsible for controlling and managing all four cylinders on bank one equally, but have no responsibility for bank two?"

If you are getting misfires only at idle on cylinders 1, 2, 3, and 4, intermittently, then you would think it's most likely there is some common denominator affecting all four cylinders equally.

So, VANOS? Throttle Actuator? Bank 1 specific wire harness commons, what else is responsible for all four bank 1 cylinders?

I still question your throttle actuator. I know you say you've checked it, but I don't have much confidence in that inspection unless you have physically swapped it with with another one and still see the same problem. How does the car run without the intake plenum on? any different?

I would find it very odd that you have broken valvetrain parts all four bank 1 cylinders, especially since the car revs and appears to run normally above idle (seeing that you can hold 2500rpm until the car warms up, which is a long time).

Another thing to reconsider: It is very common for a technician to inspect a part and believe that it is good, when it's not, and it leads them down a completely wrong path based on incorrect findings.

[Woes_M3]

Apologies if I missed this in the previous posts, but have you replaced the o2 sensors? I was getting intermittent whole bank misfires. After I had changed my o2s it went away. I'd sometimes get rough idle and car would enter limp mode.

[tdott]

Originally Posted by Woes_M3

Apologies if I missed this in the previous posts, but have you replaced the o2 sensors? I was getting intermittent whole bank misfires. After I had changed my o2s it went away. I'd sometimes get rough idle and car would enter limp mode.

I've swapped the pre-cat o2 sensors bank to bank, the codes didn't change. Also monitored the voltages under various conditions and nothing seemed out of the ordinary, there are also no o2 sensor related codes. They have been replaced before probably within a few years, and the car only has 49k miles on it.

Still possible, will potentially look at swapping them with another set if something else doesn't pan out.

Also wanted to note that the guy with the bank 2 harness issue was getting O2 and SAP related codes, which we aren't seeing here, also his misfires weren't at idle when cold. His codes were:
2729: DME: Oxygen sensor, coast-mode diagnonsis before cat., bank 2
27B1: DME: Secondary air system flow rate, bank 2

None of those are present yet.

[omgzirra_exe]

Originally Posted by tdott

2729: DME: Oxygen sensor, coast-mode diagnonsis before cat., bank 2
27B1: DME: Secondary air system flow rate, bank 2.

these are basically my codes right now. i just forgot which bank it was, but im pretty sure it was bank2. but i dont think this is why im bogging at 3k rpm when i decide to go WOT and pass someone, i should be able to just foot down and drop a gear and let the DCT decide the optimal gear to use..

[tdott]

Originally Posted by MineralWhiteF80

I still question your throttle actuator. I know you say you've checked it, but I don't have much confidence in that inspection unless you have physically swapped it with with another one and still see the same problem. How does the car run without the intake plenum on? any different?

I am planning to do more testing around the TA and ICV piping. Seems like ICV related leak/crack somewhere might be a potential issue.

Originally Posted by MineralWhiteF80

I would find it very odd that you have broken valvetrain parts all four bank 1 cylinders, especially since the car revs and appears to run normally above idle (seeing that you can hold 2500rpm until the car warms up, which is a long time).

I agree, but wanted to rule it out.

Originally Posted by MineralWhiteF80

Another thing to reconsider: It is very common for a technician to inspect a part and believe that it is good, when it's not, and it leads them down a completely wrong path based on incorrect findings.

I agree, it's also very common for others to throw out unrelated solutions because it fixed someone elses/their problem, while ignoring the differences in codes thrown and fault behavor. Then others just throw parts at it.

[tdott]

Flashed the tune back to stock and so far can't reproduce the issues.

It idled for 15 mins from cold, it usually throws the codes 3-4mins cold.

Turned it off and on a few times, while I moved cars around, went back inside did some stuff, drove it for 20mins. Let it idle for a while.

So far no codes have come back and I checked the ISTA combustion quality again and now bank 1 and 2 are around the same, before with the BPMStageII tune Bank 1 had lower combustion quality across cyl 1-4 as shown above.

Any ideas BPMSport ?
I will try a few more drives and cold starts before putting the BPM tune back on.

Below is stock tune:

[SYT_Shadow]

I'll try to write the shortest message possible to not trigger any bans:
Change tunes.
Problem solved.

[omgzirra_exe]

Originally Posted by SYT_Shadow

I'll try to write the shortest message possible to not trigger any bans:
Change tunes.
Problem solved.

sometimes it be like that...

i hope you figure this out tdott!

i'm going to replace a few more things on my end, just a few things that are cheap while my car gets a refresh for 2024...

bought some new cam sensors and one new vanos and got a working ignition coil for my bank 8... even though mine didn't show any failure. wont know how it goes until the car is back.

[tdott]

So, still no root cause found.

Ran great on stock tune for 7 days, no additional codes, only the ones for the missing cats.

then re-loaded BPM stg II and can't reproduce the issue now. It's been 3 days of testing, when prior it was triggering the issue everytime.

Only thing that comes to mind is adaptations but those were cleared while troubleshooting and didn't make a difference before reflashing to stock.

Guess we'll wait for it to come back...


So to summarize, consistent bank 1 misfires.
Swapped, o2, coils, new plugs, new low pressure fuel sensor. Checked for leaks, checked TAs.

Bank 1 misfires were still reproducible every time, codes didn't changed, no new codes.

Flash to stock.
Issue can't be reproduced.

Flashed back to BPM Stage II
Issue can't be reproduced.