2001 GMC Yukon Random Misfire started with p0303 went to p0300

[CorbinC124]

So i have a 01 Yukon with the 5.3, had a cylinder 3 misfire (p0303) according to cheap scan tool. misfire got worse and threw flashing CEL when i pulled cyl 3 spark plug to check. moved spark plugs and wires from 1-3 and moved injector, code went away but still misfired. Installed new intake manifold gaskets due to hole in intake and a new coil for cyl 3. now have a p0300 code, still misfires although actually stalled out on engine twice before now reving to 3000 rpms and staying there. cleaned the throttle when i replaced the intake. cannot figure out this misfire. any help would be appreciated!!

 

[rockola1971]

Check individual cylinder misfire counts.

 

[Matthew Jeschke]

Check individual cylinder misfire counts.

I second that...

I have an aftermarket cam so the misfire detection doesn't work well on my engine. It maybe able to detect which cylinder is misfiring per above or at least point you in a good direction to troubleshoot.

Also you mentioned a vacuum leak, you may want to search for additional ones.

Did you install new plugs and wires or just inspect and rotate them around? How is your ignition voltage looking? Good grounds?