Idling Misfire...

Hey,

This is the second car my dad has "ruined". This one is a '03 Buick Century 3.1L, the last one was a '00 impala 3.8L. Forget about the impala for now.

I don't know why his cars get like this, but there's an idling misfire in cylinder 4.
Symptoms:
Very faint vibration in the car at idle
Code P0304 - Cylinder 4 misfire
Sputtering exhaust at idle
Ignition advance 18 deg @ idle, 40 deg @ 3000 RPM
Spark plug was covered in white


So I replaced the spark plug and wire, but the misfire is still there. The car passed a compression test.

Can you please look at the symptoms and tell me what each one means. Is the sputtering exhaust from the misfire or a leak near the new universal catalytic converter? Is this misfire due to a faulty injector? Should I check the ignition coil, and how?

Maybe he should stop buying GM cars.... ;)

You will need to figure out what is causing the misfire, lack of spark or lack of fuel (since you've already determined compression is fine). You can pick up an inexpensive spark tester or make one from an old but still good spark plug. If you have no spark, then you get to determine if the coil is being commanded to spark or not.

You could likely borrow a noid light set from your local chain auto parts store (they may have spark testers for rent as well) to check for pulse to the fuel injector for cylinder 4.

There's a good chance that instead of the new catalytic converter causing the issue, instead the misfire caused the old catalytic converter to fail.

-Rod