2008 535i with 150,000 miles. Daily driver with 100 mile per day commute. Car had been running perfect when I parked it for the week Friday afternoon. Started car Saturday morning…started normally, and within seconds, started sputtering, mis-firing, white smoke coming out of driver’s side exhaust only, CEL came on…no other lights, and I turned it off after about 10 seconds. Scanned and found “P0306 - cylinder 6 misfire”. Let car sit for 2 days, reset fault code, started it again…exact same thing, except no CEL or fault code, and no other lights. About a month ago, I had valve cover gasket replaced, oil filter housing seal/gasket, and a few other oil gaskets/hoses replaced. Any ideas?

I forgot to mention that in addition to all the other symptoms...there is a strong smell of gas when the car is turned off after the 10 seconds.

 

Check for oil in coolant and coolant in oil. Could be head gasket near #6 cylinder..

 

^ what he said. Plus, if you're talking about the smoke only coming out of the driver's side of the twin tips that exit on the left rear, there's a flap that only lets one muffler work at idle. No dual exhaust on this car.

 

1 - How can I check for coolant in oil and/or oil in coolant? 2 - How can I check for leaking head gasket? 3 - Is cylinder #6 the last one towards the rear of the car, or the front? Thanks for the help.

 

I forgot to mention that in addition to all the other symptoms...there is a strong smell of gas when the car is turned off after the 10 seconds.

 

Could be leaky injector. Can you swap into a different cylinder and see the problem follows the injector?

 

I changed all plugs and coils about 30,000 miles ago, but not really comfy to start swapping injectors. It sounds like a leaking/blown head gasket, but I'm not sure that would produce such a strong smell of gas under the hood.

Oh yeah...forgot to mention yet another symptom. When engine is running & sputtering....there is an intermittent high pitched squealing sound coming from engine bay...as if there is air escaping from something...but it is intermittent. Lots going on with this problem

 

Coolant in oil: oil will look like a chocolate milkshake. No dipstick on this car, so if you're in need of an oil change, drop the oil and see.

Oil in coolant: puddles of oil floating in the expansion tank, or if you dip a clear tube in, oil will cling to it.

Blown cylinder head gaskets can pressurize the cooling system to failure if it's combustion pressure escaping into the water jacket. A shop can do a hydrocarbon sniff test at the rad cap to check.

BMWs don't like being run for really short periods from cold then shutting down. Could be normal since the engine runs really rich from a cold start. OR: fuel leak in fuel rail/pipes. If you can smell it under the hood, take off the sound covering (4 screws) and look for wetness around any of the connections (there are 12 high pressure connections, fuel rail to injector). I wouldn't say leaking injector unless misfiring or hard starting. You can't swap the high pressure injectors - they're coded to the ECU per individual cylinder based on parameters marked on the injector body - no two are exactly the same.

Cylinder 6 is the rear one.

High pitched noise could be a vacuum leak.

Don't forget: unless you're in Africa, when you hear hoofbeats, think horses, not zebras. The simplest explanation is usually the right one. Don't go looking for problems that may not be there. Diagnose one step at a time.

 

Been there 3 months ago, cyl 1 dan 5 misfiring, change new coils, cyl 5 still misfiring. Open the spark, and surprised for oil around spark at cyl 5 and 1. Very black and oily for cyl 5 spark tip. I replaced ccv, and sparks, going well for now. A checked for cylinder compression test, a little bit lower than it should be, but still ok. I still wonder, where the oil come from, bad ccv only or bad valve seal. I just wait and see, for another symptoms in 6 months.

 

Very helpful information...thank you for taking the time to reply. I have the cover off and can see all the injectors. No leaks of any kind...and no gas smell at all as car sits. The gas smell is only present when the car is running, and then for a while after it is turned off. No oil present in coolant tank. No milky stuff on oil cap. I think I am just gonna have it towed to my indy mechanic and have him fix it.