Missfire issues

97 grand prix 3800

To start off about 3 months ago I was having issue with the #3 cylinder(p0303). After changing plugs, wires, intake man gasket, and the pigtail going to the injector I found frayed while replacing the gasket it seemed fine for a while.
Then after only driving it around town for a few months we took it out of town and the first hill we went to climb it started missfiring again only this time the #4 (P0304). The pigtail going to #4 injector looks fine, I pulled the plug and it also looks fine. This time also you could hear the backfire from the engine and the jerking from the engine. I also checked compression and it was fine also.

The only thing I can think of next is camshaft/crank position sensor or maybe EGR valve, would I be on the right track or am I missing something else.

have you tried switching around the coil packs to see if the misfire jumps to another cylinder? i guess I'm unfamiliar of what you are talking about when you say "pigtails"?

pigtail= plug going to injector with about 6" wire so you can solder/heatshink tubing them into the harness.
I thought about switching the coil packs around, maybe I should do that next.
I'll head out in a few min.'s to try that.

Check the #4 spark plug for cracks in the ceramic insulator, as it's easy to damage them while installing and it can take time for the crack to work it's way through to cause a mis-fire. Also double check that the plug wire is on tight at both ends on the offending cylinder. Checking injector pulse and compression on cylinder 4 would be my next step to determine what is cauing the mis-fire, as well as checking spark pattern with an induction type timing light.

Ok tried switching coils, no dice. I pulled the #4 plug back out and looked it over real well. There was a mark in the insulator that may be a small crack so I went and picked up a new one. I also picked another new set of premium plug wires as last time I replaced them I didn't have much money and purchased the really cheapy ones. I'm getting ready to go out and see what it does. I cleared the code so I will know shortly if any of this helped or not. I will post back and LYK.

Update: I drove it on the hwy for 40 miles up/down hills and it didn't missfire once. Hopefully this will take care of it, I will be taking it on a 190 mile round trip next Monday so that will be the real test.
Wife wants a new car but this one's body is mint condition and only has 79k miles on it and it's a 97.(Old school teacher had it :) )

Nice work. best thing about that car is its PAID OFF!

Who cares if you have to keep repairing things here and there? Its still cheaper than a monthly payment on a new one.

Thanks for the feedback, it's nice to know you got her fixed and it was fairly simple. I hope you had a Merry Christmas, and have a Happy New Year!