Cylinder misfire enigma...
 

I have a 1997 saturn sl2, very long story short, broke down awhile back been working on it since, after getting it running again I started getting misfire in cylinder 3 code; what I've done to troubleshoot n fix that is replacing all coil packs and the module they sit on and I cleaned all bolt and the area the module rests on before installing the new on, replaced all spark plugs, map sensor, replaced all fuel injectors and cleaned fuel rail in process, replaced crankshaft position sensor and upstream and down stream O2 sensors, none of it fixed the misfire code. So finally I replaced intake manifold and exhaust manifold gaskets, Intake manifold gasket being replaced fixed the misfire in cylinder 3 finally.
now cylinder 4 is misfiring....idk what else to do or how to go about troubleshooting. I don't understand why cylinder 4 was never misfiring durng this whole process of trying to fix the cylinder 3 misfire code, and once I replace intake manifold gasket the cylinder 3 misfire code went away and now it's cylinder 4 misfiring.


Someone help me lol

I think theyre prone to intake manifold gaskets failing iirc.

Double check to make sure the plugs are snug. Everything is seated properly. And check the wiring harness to be safe

DD,

The SOHCs were the ones prone to sucking in the intake manifold gasket and that was on number one. Not the dohcs.

That's quite a bit of money in unnecessary parts.

If the misfire in four started immediately after intake manifold gasket replacement, I suppose it is possible the NEW gasket is not sealing properly.

With the car at idle, spray all around the number four intake where it meets the engine with throttle body cleaner. Do the underside as well.

If the idle is affected, then you have found the reason for your misfire, a vacuum leak.

There is also the chance that the Miss on number four is completely unrelated to anything previously seen.

Breed up on the net about the correct way to do a compression test, then go to AutoZone or similar and do a loan a tool for a compression tester. it is free.

Are you getting any other codes besides p0304? Please post results.