Sporadic Misfire

[nick.tsantinis]

1994 325, 5spd, ~133k miles

The car exhibits what seems to be a sporadic misfire. While driving it will randomly 'buck' as the engine presumably cuts out and the rpms drop for about half a second. No correlation with speed or rpm, competly random.

Be advised that this began occuring almost immediately after a serious rain event with some pretty deep water. Therefore Im convinced there is a connection. Also, Im past due for a spark plug change/tune up and will include that while diagnosing this.

Is it typical for ignition components (coils, ECU, etc?) to be damaged by water? Any other advice?

Thanks,
-Nick

[markdas]

sounds like you need to do the tune up items first, the rain/water event could be totally unrelated.

Change the service items you mentioned, do you have an OBD2 connector on that model, if you do, pull the fault codes to see if a coil is throwing anything out?

Rain and heavy water splashing up into the engine bay can cause misfires, poor connections etc or dislodge hoses or connectors, but you would normally see something obvious.

[nick.tsantinis]

Thanks Mark,

Car has OBD-I not OBD-2. I honestly haven't even opened up the hood yet. Until yesterday i thought it was an ACS problem, but when it occurred with the ACS off I realized that the flashing light was the 'Check Engine' and not the 'ACS' light.

I will do some digging this weekend. Any idea what the plug gap is?

Thanks again,
Nick

[Jared at Pelican Parts]

Pelican Technical Article: Reading BMW Fuel Injection Fault Codes

Give this a read and see what codes you have.

[Manolito]

Spark plug gap does not matter unless you drop a plug and really close it. You should not use plugs that have been dropped anyway (don't want broken glass falling into a cylinder).

I suggest the inexpensive two-electrode style plugs, such as the NGK BKR6EK or the Denso K20TXR. The single-electrode precious metal racing plugs don't seem to help in the RPM range that a stock engine runs, and though it may be my imagination, these cars don't seem to run as well with the four-electrode plugs that come stock in the e46s.

Probably worth unplugging every low voltage connector you can find under the hood to make sure that they are all clean and dry and corrosion free. Also, an occasional 'buck' can be caused by water in the gasoline. A bottle of HEET added to the gas tank might not hurt.