Thread: Misfire on cylinder 3 and 4

Anybody have trouble with a 2004 supercharged grand prix with a misfire in cylinder 3 and 4. Especially under heavy load with pedal 3/4 to all the way down.

Check engine light is blinking. Both spark plugs showing misfire.

The catalytic converter does need to be replaced.

Compression is good.

You can tell a little rough miss during idle but no codes during idle.

Anybody have this trouble before?

Have you replaced the plugs and wires? Or the coils? Or the ICM?

Just because your converter is good doesn't mean squat...get a tune-up if you haven't done one...oil/oil filter/PCV valve, etc.

Clear the code from the PCM.

Then enjoy your car not hating you.

Also, welcome to the site...

Replace your cat before you hurt the motor.

The likely reason behind 3 and 4 misfiring is they are the two middle cylinders in the front and rear. Therefore naturally they tend to run hotter than the other 4 cylinders.

Now add back pressure of a bad catalytic and you heat them up even more leading to misfires, probably knock and potentially damage.

I thought it said the coverter was GOOD.

Nevermind.