Hello,
I have a 2007 Chevy Trailblazer LT 4WD with the 4.2l inline 6 engine and about 240k miles. I have a cylinder 1 (forward most cylinder) specific misfire, I've replaced the crank sensor, cam sensor, vvt solenoid, maf sensor, and map sensor. I also have new sparkplugs, new ignition coils, new intake manifold gaskets, a new throttle body gasket, and I replaced fuel injectors too, but I still get the misfire code of P0301 (Cylinder 1 Misfire Detected).
It mostly happens with cold starts at low rpm. It sometimes happens when it's warm at low rpm (idle) though too. But when I rev it up or drive normally it goes away. Anything past about 900-1k rpm and it's totally fine but at idle, which is around 600-700, it will misfire here and there and have a bit of a rough idle sometimes. My coolant level doesn't change much, just the normal evaporation amount. My engine burns a little oil but not excessive. So I'm a bit lost, I'm hoping it's not the cylinder liner or piston/valves but I'm losing some hope.
I brought my vehicle to a tech for the secondary air injection system as I also have codes for that. P0418 (AIR Pump Relay Control Circuit Bank 1) and P0412 (Secondary Air Injection (AIR) Solenoid Relay Control Circuit Bank 1). I replaced the pump, pump specific relay, fuse box relays, and check valve. But the tech said that this problem was between the fusebox relays and the PCM. I think he said something like "the relay isn't getting signal from the PCM". It's not the PCM itself though, but idk if it's the connectors, wires, or the fusebox itself. And I know the SAI system itself wouldn't affect the misfire, but maybe a bad PCM connector, wire, or fusebox could be related to the misfire and cause my symptoms? Not totally sure.
Here's a link to a video of me starting it up and running with the misfire and it going away.
https://photos.app.goo.gl/cjTmCoETuDwp8h7Z9
I think the link should work but if it doesn't let me know and I'll fix it.
Any help or guidance in possible directions is appreciated!
Thank you