Misfire Problem

[aespen]

I have owned a bone stock '97 M3 sedan for 1000 miles (86K). The CEL has come on 3 times. Each time it resets after 3rd start.

OBD-II tells me this:

P0300 Random/Multiple Cylinder Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0304 Cylinder 4 Misfire Detected

On one of these events the engine suffered a dip in power. Two events were under acceleration at ~5K rpm and one was just cruising at 3K.

I am suspecting plugs, connectors or coils and will be replacing the first two and inspecting the 3rd this weekend. Also still need to go through my service record pile to see when plugs were (if ever) changed.

Looked through the forum but didn't see any posts exactly matching this. Any commentary or advice on this one will be much appreciated! This forum has been an excellent resource so far.

Andy

[JamesM3M5]

The coils and HT leads down to the plug are separate parts. Try swapping out just the leads and plugs frst. There are several supporting vendors that have plugs and leads available, shouldn't break the bank.

I always heard that if a coil goes bad, it goes BAD, not just flaky.

Also check for oil leaking into the spark plug holes due to hardened valve cover gaskets. This will be obvious when you pull the coil to get the plug out. Have Brake cleaner and compressed air handy to blow the holes clean if this is the case.

[JamesM3M5]

Oh yeah, I like the performance of the NGK BRK6EQUP plugs. There is a discussion on a thread I started a couple weeks ago here in the M3 forum.

[aespen]

Thanks. Ordered the NGK plugs and got the connectors. We'll see how it goes from there.

[aespen]

Replaced the plug connectors and installed the NGK BRK6EQUP plugs. Old plugs had 50K on them and there was some evidence of slight cracking on the ceramic surrounding the insulator. The new plugs made a small but noticeable improvement in off-idle smoothness. Put over 500 miles on the car since and no CEL.