P0306 code, rough idle, and white smoke from exhaust.

[chsams_]

Hey all,

just recently purchased a 2015 m4, and 3 weeks in, while i was doing WOT on freeway, car threw up drivetrain malfunction. code says p0306 for engine misfire. Car also shakes during idle and has white smoke coming from exhaust. Initially I thought it was spark plugs, but doing more research, I am now more afraid that it is the head gasket. Has anyone faced this problem before and I was wondering what to do. is there a way to check if it is gasoline or coolant coming from exhaust?

[theweebabySeamus]

If it's gas it'll smell like gas. Need more details, how many miles, are you tuned, running e85, etc?

[chsams_]

Originally Posted by theweebabySeamus

If it's gas it'll smell like gas. Need more details, how many miles, are you tuned, running e85, etc?

Hey, I'm completely stock at 68k miles. Did a 75-100 WOT and after I let go, got a drivetrain issue.

[TopJimmy]

If you can check logs then look for STFTs different on one bank versus the other. That would indicate a drippy injector. Exhaust tips stinking of fuel is another indicator.

Pull plugs and look for a bad one, maybe oiled or fueled up would prove a drippy injector. If one broke you change only that one, and also do an oil and filter change.

If you start your engine cold with the radiator cap off do you get bubbles or pressure (from compression gas seeping past a bad head gasket)?

LMK how it goes.
-TJ

[chsams_]

Originally Posted by TopJimmy

If you can check logs then look for STFTs different on one bank versus the other. That would indicate a drippy injector. Exhaust tips stinking of fuel is another indicator.

Pull plugs and look for a bad one, maybe oiled or fueled up would prove a drippy injector. If one broke you change only that one, and also do an oil and filter change.

If you start your engine cold with the radiator cap off do you get bubbles or pressure (from compression gas seeping past a bad head gasket)?

LMK how it goes.
-TJ

Hey, update,
I ordered new spark plugs and they arrive tomorrow, so I started taking the engine apart. once i took the old plugs out, I didn't really see anything visibly wrong with them. My brother took an inspection camera and put the cord down the cylinder and we saw yellowish/brown stains as well as black stains. My brother says that he thinks it might be coolant and the head gasket is blown. How accurate is this? Even if I get my engine to stop misfiring, should i still take care of the stains or is it completely normal.

https://postimg.cc/gallery/4J0vMk7

[TopJimmy]

Stains are normal. Here’s an example from my engine. You can see the “paw print” left by the injector pattern. This first example is very clean from me running E50 mix. The second example had a tiny bit of oil leaking past a plug thread (valve cover not tight enough in that spot, Doh!) so you’ll see a little more carbon buildup. The little droplets are oil from disassembly.

[TopJimmy]

Your pistons look “washed” where some liquid has cleaned the faces. Maybe it is a head gasket?

Compression test is next for leak down.

Any chance you’ve used that CRC spray in valve cleaner???

[chsams_]

Thanks for the help so far, this car has been serviced at BMW for its entire life, so I am unsure if the pistons has ever been sprayed. As for compression test, I just ordered a gauge and it should be arriving soon. When I checked the oil, I noticed the oil smelled like gasoline. Is this normal or could this indicate something?

[theweebabySeamus]

Not normal, and further evidence of an injector issue.

[TopJimmy]

Here’s an example from a buddy’s YouTube where he had a S58 injector stick open pretty badly. You’ll see piston #1 is completely washed, while #2 has the normal dark residue.

[chsams_]

Just pulled the plugs and coils, noticed spark plug 6 is significantly darker than others. Compression test arrives today, and will test later today. Does plug being darker than others signify anything?

https://postimg.cc/gallery/G2dcvfZ
first picture is cylinder 5 and 6, second picture is cylinder 6 and 1

[chsams_]

Originally Posted by TopJimmy

Here’s an example from a buddy’s YouTube where he had a S58 injector stick open pretty badly. You’ll see piston #1 is completely washed, while #2 has the normal dark residue.

Hey, just replaced sparks and coils. Engine is still misfiring. I have a carmax warranty with a $1,000 deductible, and I am wondering if at this point, I should file a claim. Apart from spark plugs and coils, is there any other factor that could cost less than $1000 including labor? Thanks for all the help.

Forgot to mention that compression test seems fine; all within 10% of each cylinder.

[TopJimmy]

Replace the one injector. It’s relatively easy.

[chsams_]

Originally Posted by TopJimmy

Replace the one injector. It’s relatively easy.

replaced injector, still misfiring, smoke has turned a little blue. gonna take into bmw tomorrow and try to diagnose it. Thanks for the help.