What can be the cause of a misfire?

Hi there! I may be able to provide you with info that we have in general knowledge from working in a dealership and having customers come in with a misfire. Firstly, you say that you’ve replaced your plugs. Make sure they’re all fairly tight, not too tight you don’t want cracked heads. Just double checking has solved it in some cases. Check those wires, and make sure they’re fully seated in the coil packs. We also pack the connections with dielectric grease for good measure. I’d also go around and see if you’ve jostled any connector that involves the ignition system (i,e, the coils, the wires themselves, the line from the ECU to the coil(s) and make sure they’re not flapping around. Finally, if all else fails, I’d try and, if you have them, swap out your OEM ignition components and see if the problem persists. Anyway, best of luck to you man. I bet someone’s who’s been around GM vehicles might have a specific fix, but these are things we try to do if we can’t have access to a certain manufacturers TSB’s or shop manuals.

Did you mix up the wires? Accidently damage one when installing them?