OK, been working on a red GTP for a while now. It'* a fast car, low 12s in the 1/4
Last week I get a text saying I blew my motor. I'm like what? I was working on it yesterday and everything was fine. He said I drove home but it'* running rough. Well, then you didn't blow the engine. After many text messages I determined the engine was not blown but running rough. I gave a few suggestions for him to check, including pulling the valve covers and inspecting the valve train.
Monday he comes over and we start poking around. We changed the MAF last week so I said put the old one back, no change. Hmm, feels like a miss, but nothing shows up on the scans. Only odd thing is the LTFT was -10 to -13. Why so rich I think. Hmm, perhaps a cylinder isn't firing. We test the coils, find nothing but swap them out anyways. No change. Test the plug wires, and swap them out just for giggles, no change.
By this point another friend showed up to help. Now 3 of us trying to fix this problem. By this point we figured out it'* not the ignition system. But we can smell gas in the exhaust.
OK, pull the plugs. #5 is black, the rest look good. So 5 is the problem, this helps. But why? We decided to pull the injectors, perhaps #5 is stuck open. We move it to #1 and swap the plugs as well. Start, and no change. Pull the plugs again and #5 is starting to turn black.
OK, it'* not ignition, and it'* not the plug or injector. I say there'* only one thing left and that'* a mechanical. Out comes the compression tester. Everything checks out, including #5 By this time it'* getting late. Not a clue what'* going on here.
Well, finally broke down and pulled the valve cover.
One broken spring. The way it broke the valve still closes, this is why the compression test was good. But when running I'm guessing the valve started to float. What a pain.