Misfiring fault that im unable to solve

[FatFingers15]

Hi Guys

First post here but regrettably its about problems the car is facing.
buckle up, its going to be a long ride.

Some background info, i recently took over a 2009 E90 LCI M3 DCT with more than 130k miles on the clock. Previous owner had spent quite a bit of time and money maintaining and repairing it so i took a leap of faith and bought it.

However after a few days in, i realized there is weird bucking feeling or jerk like an engine brake whenever im around the 2.5k rpm range, when im just cruising on the highway. i initially thought it was the throttle let off being extra sensitive or just my butt meter is wonky. After a few more days, the feeling got stronger and eventually it threw a CEL and went into limp mode. Anything below or above 2.5k it cruises fine, no issues if i give it a harder throttle. No difference in D or S or any DCT setting.

I dont have a video during cruising, but i do have a video of it in neutral, watch how it dies around the 2.5k rpm with constant low pressure but with high pressure it works fine.
https://youtube.com/shorts/Hiw1ItN51wo?feature=share

Here's another video of it going into limp mode and heavy misfiring. There is a weird sound from the engine, like a suction or vacuum sound, have no idea what that is.
https://youtube.com/shorts/4bYELZ671dk?feature=share


Here are some of the faults i managed to scan at a shop and myself with a foxwell530.

Idrive
Engine Fault
DSC failure
DBC failure
FTM system error
Start assistance inactive

Codes
27AF Secondary air pump
2771 Oxygen sensor dynamic diagnosis bank 1 (went away)
2772 Oxygen sensor dynamic diagnosis bank 2 (went away)
2B0D Idle actuator monitoring bank 1
Misfire impairing exhaust emission on all 8 cylinders
Misfire with cutout on all 8 cylinders (just got them today)
27C1 Tank empty on fault entry (went away)
P1411
5E19 DSC (went away)
9319 Fuel-level sensor left (went away)
9319A fuel-level sensor right (went away)
A6CF Auc sensor

There were no specific throttle or idle actuators faults, neither is there any fuel pressure or 02 sensors fault. Before you make any conclusions, these are the items changed

Fuel sender and tank (replaced in 2018)
AGM battery (replaced in 2018)
O2 sensors (replaced in 2019)
Upgraded throttle actuators by Rebuild.org.uk (2019)
ICV (replaced in 2019)
Accelerator module (2019)
ABS sensors (2021)
Coilpacks (35k mileage)
Spark plugs (replaced last week)
LPFP (replaced last week)
Mid pipe exhaust seals (replaced in 2020)

Car is not tuned, has a M performance exhaust, stock air box with k&n filter. feeling super lost now and have no idea what to do next.

[nycplumber]

I would check for vacuum leaks. I would also run multimeter under hood to see how many volts you're pulling when car is on/off. When these batteries hit 12v they start to cause issues.

[amrazM]

Usually a icv does produce these codes, generally a single ramp factor not ok still yields a working icv but there is still a problem with your icv. you sure it was replaced with a new part?

[Redd]

You probably have two separate issues. The DSC, DBC, FTM errors should be wheel speed sensor. Common fault, change all 4.

Now on to the engine. 8 cylinder misfires usually point to an intake issue, usually an air leak somewhere. I would remove all components and do smoke test to check for air leaks. This includes all the connectors that go into the chargepipe and plenum. Pay particular attention to the intake air temp sensor hole at the plenum. There should be 4 small locating tabs just inside the hole. Improper/forced removal of IAT sensor could damage these 4 small tabs and air can leak in under vacuum. The rpm range where your problem occurs - between 2-3k rpm, part/low throttle - is also the range where high intake vacuum occurs. I personally experienced this. Took me weeks of troubleshooting before I found the culprit.

Prolonged misfiring can damage the O2 sensors (again from personal experience). So once u find the root cause, symptoms may persist slightly even without errors due to damaged O2s. Be prepared to change those out too.

Good luck! I hope these tips help in some way cos air leaks are a bitch to diagnose.

[FatFingers15]

Hi all

Sorry didnt log in for a few days so i didnt know there were replies.

Anyway a quick update, the misfiring is now only on cyl 6 and 7. I changed those 2 coils and car seem to work fine for a but heavy misfiring returned shortly after. Now its to the point where by the car will just start in limp mode and misfires. Clearing the codes didnt help.

I bit the bullet and changed all 8 coils, oem was not available anywhere so had to get the originals. BUT, the misfires did not cease. 6 and 7 was still misfiring and the diagnostic showed the entire bank 2 was faulty, figures were way off. A deeper scan showed that 6 and 7 had a "short circuit to positive" message. Mechanic suspected that the dme is fried.

Originally Posted by nycplumber

I would check for vacuum leaks. I would also run multimeter under hood to see how many volts you're pulling when car is on/off. When these batteries hit 12v they start to cause issues.

Thanks, battery was checked just today and is working fine. Will the vacuum leak cause that "whoop" sound?

Originally Posted by amrazM

Usually a icv does produce these codes, generally a single ramp factor not ok still yields a working icv but there is still a problem with your icv. you sure it was replaced with a new part?

Thanks, but thats the thing, the owner said he had changed them, whether or not it was used or even changed is not verifiable but no reason to doubt at this point as the fault was no longer present. The ramp factor is back to normal now. So hopefully its not the issue.

Originally Posted by Redd

You probably have two separate issues. The DSC, DBC, FTM errors should be wheel speed sensor. Common fault, change all 4.

Now on to the engine. 8 cylinder misfires usually point to an intake issue, usually an air leak somewhere. I would remove all components and do smoke test to check for air leaks. This includes all the connectors that go into the chargepipe and plenum. Pay particular attention to the intake air temp sensor hole at the plenum. There should be 4 small locating tabs just inside the hole. Improper/forced removal of IAT sensor could damage these 4 small tabs and air can leak in under vacuum. The rpm range where your problem occurs - between 2-3k rpm, part/low throttle - is also the range where high intake vacuum occurs. I personally experienced this. Took me weeks of troubleshooting before I found the culprit.

Prolonged misfiring can damage the O2 sensors (again from personal experience). So once u find the root cause, symptoms may persist slightly even without errors due to damaged O2s. Be prepared to change those out too.

Good luck! I hope these tips help in some way cos air leaks are a bitch to diagnose.

Thanks, thats a very specific area, i can imagine the headache u went through. What u said makes sense, i'd probably do the same. Yeah im standing by for the o2 sensors just in case. Just hope i find the root cause soon enough.

Currently the dsc faults didnt return, so i hope it was sort of collateral damage from the misfiring. If it comes back on, i'd probably change those for peace of mind and also to rule out those parts.