I’ve never been so stumped, 2004 Suburban
Sorry about the language on video, didn’t think about it when I made it! So, I have a 2004 Suburban 5.3 Vortec. 215,xxx miles. Po300 random cylinder misfire. Symptom, idles rough, runs rough under load. 1500 rpm no load the motor smooths out, 2000 it’s rough again, 2200 or so it’s stable but the cel will flash. It seems like it has a burnt valve, but I know it doesn’t, heads and block are in great shape. It’ll suck a dollar bill back in the exhaust but if you listen it’s not a consistent with one cylinder in firing order. You can hear it in the intake as well. I’ve replaced head gasket, valve seals, cleaned heads, polished (to help fight future carbon build up) and lapped valves, resurfaced heads within .0015 with spec being at .0040. Replaced valley pan gasket, intake manifold gasket, fuel filter, throttle body sense iac valve and tps are non serviceable, I installed an after market intake because I read that the plastic resonators on the Chevys like to crack and leak air. I also went to the junk yard and switched my pcm to see if it was a computer issue. Runs the exact same. I checked spray pattern of fuel injectors and they’re flawless.I saw a great video where a guy who works for a shop ran the o2 sensors at open loop and it immediately remedied the problem, the heater wire(?) was good but one o2 sensor was stuck open and the downstream was completely faulty. I don’t own the equipment to do that. What can I check? The valves looked much better in person!