P0302 is a misfire on cylinder 2, Can be caused by multiple things, A bad plug, bad coil, bad wiring to the coil, bad driver in the PCM bad injector. Or through a mechanical issue like a damaged valve or piston. What I suggest is to take the coil from say cylinder 4 swap that with cylinder 2, now pull the spark plug, inspect it, if you don't see a crack or carbon tracking, swap it with cylinder 6. Inspect the wiring for any damage, mice and rats love to climb onto a warm engine and then chow on the wiring, also look for anything like a rubbing harness where it goes through a bracket or over a corner. Now that you have moved parts and inspected the wiring, clear the codes. Start it up and see what code(s) show up now. Lets say it now shows a P0306, well 6 is where you put the plug. I would swap all the plugs as it's possible it was cracked or damaged on install. However, instead you still have the P0302 code. Well that means you need to look at the injector and in cylinder issues. As you didn't list the engine (there were 9 available) it's hard to tell you the testing process. However the engines like the 4.3 and 5.3 with active fuel management have a lot of issues with the lifters in the system failing. For the rest you would end up testing the injectors using a scan tool and pressure gauge as well as a meter to check resistance. Plus doing a compression test to see if it is valve related.
But swapping the parts around will cost you time and may show the problem.
May 22, 2026 at 1:57 AM
