[Onizer]

Hi,

My 06 n54 335i 6mt has been getting misfires for like a week now.

It started happeneing after i swapped plugs for bosch ZRG6STE2's.

3 codes show up :
29cf combustion misfire, cyl 3
29D0 combustion misfire, cyl 4
29cc combustion misfire, multiple cylinders

the 29d0 (cyl 4) does not come instantly but after driving a bit (20-30 minutes) and is not missing as bad as cyl 3.

Little bit of context:
I replaced my valve cover + gasket 2 weeks ago -> car ran fine
a week later i saw some oil leaking and my oil gauge showed +1L (i was just above the mini when i replaced the vcg)

So i went ahead and decided to check my work (didnt have a mirror or an endoscope with me when i did the VC), so i removed everything as if i was to do the vc again (in case the seal was pinched) : plugs, wiring harness, pcv tube, disconnected the positive and negative wires next to the washer fluid filler neck, removed the dme cover to lift wire grommets. (didnt touch the high pressure fuel lines)

The seal was ok all around but was wet close to the n°5 plug and there was some oil on the coils 5&6, so i retightened the valve cover to 12nm instead of the 9nm (just to be safe).

while i was in there i replaced the bmw bosch plugs for 6x bosch ZRG6STE2.
i ended up replacing only 5 because on one of them the electrode poke out a little bit from the 3 "tips?" (visually different compared to the other ones). the cyl 1 plug was the one i didnt replace while waiting a replacement one.

Since that moment i got a persistent cyl 3 misfire, i swapped the cyl 1&3 plugs (so i put an old plug on cyl 3), temporarely fixed the misfiring but it came back after 30 mins of driving.

i then did these things :
-> put a new bosch ZRG6STE2 on cyl 3 : didnt fix
-> swapped coils 3&4 : didnt fix and started getting sporadic cyl 4 misfires now
-> put a new NGK coil on cyl 3 : didnt fix
-> Put the old cyl 3 coil on cyl 2 : no misfires on 2 (so old coil was fine ig?)
-> put back old plugs on cyl 1 to 5 (not on 6 because i didnt remove the cowel, planning on doing that during the week. : didnt fix

i visually checked the wiring harness and dont see any worn wires or tears, all connectors are properly secured and gounding points are tight.
i will electrically check the wiring this weekend, but i just dont get why mlsfires started after swapping plugs...

one time while driving it started missing really bad and it threw 29ce and 29d1 (misfire cyl 2 and 5), they didnt come back since (post spark plug replacement).

Im geniunely lost and dont understand why its misfiring, did anybody experience the same issue or similar ?

Thanks

[Onizer]

I read A LOT of threads about misfires but didnt help

[Sgop335]

doesnt look like the plugs are issue, since you have swapped some "known good" ones and misfire persist?
How about coils, known good ones swapped?
Then it trickles down to fuel injector.

[Onizer]

Originally Posted by Sgop335

doesnt look like the plugs are issue, since you have swapped some "known good" ones and misfire persist?
How about coils, known good ones swapped?
Then it trickles down to fuel injector.

Yeah im ruling out plugs now, i tried one new coil on cyl 3, witch didnt change anything, the coil from cyl 3 is on cyl 2 now and there is no issues on cyl 2.

cyl 4 misfire is almost instant now, and yesterday i got the code for cyl 5 misfire once.

Slowly starting to think that my DME is going bad, will have to check it too.

[Onizer]

This morning at cold start it felt fine and started misfiring after 5 minutes of driving, weird

[Popoto]

Since the misfire does not seem to be moving, My money is on injector number 3.

I chased similar issues for a long time, went through tons of coils and spark plugs for no good reason. Turned out that Injector 2 was leaking and would only throw a CEL sometimes on cold start (sitting overnight etc) or extended highway driving. It wouldn't always leak enough to throw a code on startup until 3-5 months after it started acting up, then it would throw a code pretty much every time I started the car.

It was Cyl 2, but also caused misfire codes on other cylinders at times. When I moved it to where I swapped it out, I actually got codes for misfires on 2 4 and 6 at startup.

[Onizer]

Originally Posted by Popoto

Since the misfire does not seem to be moving, My money is on injector number 3.

I chased similar issues for a long time, went through tons of coils and spark plugs for no good reason. Turned out that Injector 2 was leaking and would only throw a CEL sometimes on cold start (sitting overnight etc) or extended highway driving. It wouldn't always leak enough to throw a code on startup until 3-5 months after it started acting up, then it would throw a code pretty much every time I started the car.

It was Cyl 2, but also caused misfire codes on other cylinders at times. When I moved it to where I swapped it out, I actually got codes for misfires on 2 4 and 6 at startup.

Sorry for the late response, it was indeed the injector n°3 that failed, pretty odd that when cold it worked perfecty but hey, bmw things.

Replaced it and works perfectly now,