Hello,

I have an ongoing random misfire issue I was hoping I could get some ideas on and help point me in the right direction of solving.

History. The lower intake manifold was cracked around the coolant temp sensor so bought a new lower intake manifold to replace it and also replaced the gaskets with new Felpro gaskets.

When everything was back together the car started throwing a random misfire code P0300. I checked for vacuum leaks multiple times and nothing was found. So I replaced the spark plugs and wires with new AC Delco replacements. The problem continued.

After this I had someone with a good computer run a scan while the car was running. This revealed prominent cylinders misfires on 3 and 5 even tho all cylinders had a misfire. So took the plenum off and hooked noid lights up to the wires going to injectors and they fire just fine. Decided to replace the 7x crankshaft sensor. and the problem continued.

After all this I hooked up a timing light to the spark plug wires. This revealed that spark was being received but the spark would drop now-and-then for a brief second and continue firing rapidly. This behavior occurred on all cylinders. So swapped out the ICM and coil packs with one taken from another car. Problem continued.

The car runs fine when cold, but once it starts getting warm and the idle goes down the misfire start.

Any ideas what the problem could be now or what I could check? Cam sensor? Computer issue? 24x crank sensor? Bad harmonic balancer?

Note: The anti-theft light is always illuminated on the car. It doesn't prevent the car from starting. Not sure if this has anything to do with it, but the light was illuminated before anything of this even happened.

Thank you!

 

Having same issue did you fix it ?