Hello, I have a 2002 Buick Lesabre that has a Check engine light code saying misfire on cylinder #3. I have change the spark plug/ plug wires/ checked fuel injector connector voltage/ and swopped fuel injectors and I still have a misfire in cylinder #3.

I recently had a gasket issue (water leaking into the cylinders) and replaced the intake manifold gaskets/ head gaskets/ and plenum gasket with the help of my (airplane) mechanic father and solved that problem. I didn't have a misfire before the work was done.

It idles rough and is definitely misfiring but any speed above idle and it seems fine/unnoticeable.

My next guess is maybe a stuck valve arm but I'm starting to run out of ideas.
Can anyone Help me??

sometimes when you have the coolant issue it messes up the plugs, did you check the plug and wire? you can be sure by swapping one at a time to a different cyl. and see if the code changes

Switch your coils around and see if the problem follows the coil.

Thanks for the replies.

I tried:
- switching the ignition coils, misfire stayed on #3
- put new spark plug in cylinder #3
- put new spark plug wires on all cylinders
- checked compression, it was between 90-120 which was fine
- Also cleaned the MAF sensor with MAF sensor cleaner (I know a fault in the MAF senor would cause random misfire but I'm running out of ideas)

And I still have a misfire on cylinder #3?

Also I found out my heater doesn't heat up. I'm not sure when this started but I noticed it the day my car died due to leaky gaskets. I turned my heater on full blast cause my engine was heating up and no heat came out of the heater. I thought it was just low coolant due to it burning off in the cylinders but since I've fixed the gaskets my engine temp has been fine and my coolant level is steady but my heater still doesn't heat up on full blast and I don't have any leaks under the car. I'm not sure if this could be related to my cylinder #3 misfire?

From time to time, I have seen single cylinder misfires from a bad ICM

Great, thank you. I wouldn't have thought of that. Do you know if there is a way to check if the ignition control module is malfunctioning? Like a multimeter test or is there a check engine light associated with it? Also I know what the ICM looks like but do you know where it is located on the vehicle? I would guess under the ignition coils

Did a little research on ICM symptoms to give you more info on my situation:
- I haven't had the car die on me
- the misfire doesn't seem to be associated with my engine temperature it starts misfiring once I start it.
- pulled the spark plug #3, cranked the engine and it sparked

But I have completely run out of ideas and this sounds like it could be my problem.

Also does anyone know what the cylinder compression should be in PSI?

Compression test. https://www.gmforum.com/showthread.p...mpression+test

ICM test. https://www.gmforum.com/trouble-shooting-test-procedures-141/icm-test-299761/

WOW you are great! Thank you so much. I will follow your guides and write back in a day or two with the results. Again thank you!

Well I took my Ignition Control Module to autozone and they checked it for me 6 times and said it was fine.

Back to the drawing board.

Recap: Misfire on #3
- New spark plug wires
- New spark plug
- Switched ignition coils, misfire stayed on #3
- Pulled the spark plug #3, cranked the engine and it sparked
- Checked cylinder compression, might recheck
- Swopped fuel injectors, misfire stayed on #3
- Checked fuel injector connector voltage on #3, was the same as others
- Fuel line not clogged
- Cleaned MAF sensor
- Checked Ignition Control Module, its fine

Maybe cylinder rings?

Any ideas?

Compression test would have shown bad rings.

What causes a misfire?
Bad injector, you swapped them
injector plug, you checked that
Bad spark plug, you changed them
Bad plug wire, you changed them
Bad ICM, tested but not changed.
Chipped piston, need a bore scope to check.
Broken valve spring, only a visual test will show this.

So, check the piston, remove the valve cover. After that, swap out the ICM,