Engine misfiring under load?

hazmat · 11-12-2007, 03:42 PM

Hello:

I have a 2002 325xi with sport package. It has over 83k miles on it and it has started to misfire when under load, such as going up a hill. It does not do this all the time, nor does there seem to be a pattern: it will do it some times but not all the time. It will not happen when the car is cold, only when it has been fully up to temperature for more than 30 minutes (I've had it happen once when on a trip after about 2.5 hours and once after driving for maybe 30 minutes). The first time it happen, the OBD gave an error code of a bad exhaust cam sensor. This was replaced and the misfire happened again after the sensor replacement. After this time, there is no code on the OBD. Anyone have any ideas on what it could be?

Thanks.

Brett

Jeron · Jeron's Garage

How bad is the misfire? Do you hear it or feel it?

Have you checked the spark plug wells for oil and have you checked the spark plugs for wear and unusual coloration?

Another option is coils but you should get a code.

hazmat · 11-13-2007, 04:23 AM

Hello:

I can hear it and it shakes the car, steering wheel, etc. No I have not checked the plugs yet. Is this indicative of bad plugs?

Brett

Jeron · Jeron's Garage

Your description to me sounds like an intermittent electrical problem. Problems that don't throw a CEL are usually plugs or fuel pressure, occasionally injectors or coils.

This is how I would start: Check the plug wells for oil. Pull the plugs and inspect them or replace them if they have 50k on them. Change your fuel filter if it is original. The pressure regulator is built in.

hazmat · 11-13-2007, 08:41 AM

Jeron:

Thanks very much for your information. I will do so this weekend. Can you tell me more about the oil in the plug cavities? Is this normal? Is it the sign of a head gasket going or some other serious problem?

Thanks.

Brett

hazmat · 11-13-2007, 08:42 AM

Jeron:

One other thing - if it was a coil, wouldn't run like this all the time, no matter what? I had an 02 Audi A4 that had the coils go (twice, both times replaced by the Audi recall) and in each case no matter what you did, the coil stayed bad.

Brett

Jeron · Jeron's Garage

Oil in the plug wells is common and a sign of a bad valve cover gasket, not a bad head gasket. It is very common although usually the outer valve cover gasket fails first and you see oil or smell oil before the plug well seals leak too much.

Coil failure can be intermittent and situational. Here is one from yesterday:

Idle vibration, vibration until 2500 RPMs

kneegroh420 · 12-12-2007, 08:49 PM

i have a 1999 328i and i am having the same problem as brett with misfiring. my car has done it once since i owned it (april 07) and once it started getting cold out, usually everyday in the morning. the code i got was a misfire in cylinder 3. so i decided to changed the coils, plugs and connectors, but before i did that i ran two fuel system cleaners (chevron techron) through before i changed them. after i ran one through the car was not misfiring anymore, the idle will dip real low all of a sudden then jump back up. so i changed the coils, plugs and connectors and sure enough the car still misfires. so should i be looking into the fuel filter next or does that point toward something else??

thanks,
justin