99 Isuzu 3.2L P0300 code
I legitimately need help tracking down the cause of this misfire. I replaced the head gaskets a while back, and ever since then it’s been running, but I get a misfire. I replaced the plugs, manifold gasket, cam and crank position sensors and today I tested the fuel pressure. It was at 40 PSI in the on position primed and ran at 36 PSI steady. I also replaced the injector O rings and caps to make sure those are sealing and not causing a vacuum leak. From what I tell there isn’t any raw gasoline in the fuel pressure regulator, but maybe I’m just not seeing it for some reason. The only code it’s throwing is the random misfire. I’m running out of ideas after today when I checked the fuel pressure. I just don’t want to keep throwing random parts at it anymore. I swear it’s in time, but I’m not sure how it would run if it was off by a tooth. I know that if it was way off it wouldn’t run at all. The serpentine belt tensioner is hopping up and down about an inch when it runs. I can post a video of it running if anyone thinks that would have a better idea. I just feel like I went through all the common causes of misfires in the 6VD1. I almost want to replace the FPR, but if it’s just more money down the drain without solving the issue I’ll be very bummed out.