a miss while running

[pontiac3.4]

i got a 95 grand prix gtp with a 3.4 and i got a miss when running on number 3 and 5 cylinder. i have change the plugs,wires,coil packs and it still has a miss does anybody have any ideas.

[GTP Dad]

Ignition module or fuel injector. Either can cause the issue.

[pontiac3.4]

Originally Posted by GTP Dad

Ignition module or fuel injector. Either can cause the issue.

i had the ignition module tested and it is good, would one bad injector cause that on two cylinders

[GTP Dad]

No, one thing to check is if the two cylinders are fired by the same coil. If so that may be the issue. Sometimes even new coils can be bad and causing problems. An easy way to check is to switch the coils and if the misfire changes to those cylinders then you have the solution. One other thing make sure the wires are on correctly. A simple item but can cause the issue you are speaking of.

[richtazz]

Since it's 2 adjacent cylinders, I'd do a compression test. The 3.4 DOHC is known for head gasket issues, especially if the engine ever got hot. The head gasket may be blown between cyl's 3 and 5, causing compression to leak between the two. This would cause a miss, and a compression test would verify.

[GTP Dad]

Thanks for the insight Rich. Forgot about the gasket issue. I concentrated on the ignition and fuel problem. Guess I am getting old afterall!