P0300 Random Misfire issue
I have a LS1 GTO cat delete that is having some serious misfire issues. The check engine light flashes at 2000 to 4000 rpm, the light stays on at idle (rough idle) and no misfires over 4000 revolution. I check the wiring and nothing seems to be out of order and tried to detect which cylinder is misfiring but it's every one of the cylinder misfiring at random!
background: 04 LS1 GTO 62k miles. The car has headers, straight pipes, cat delete with diablosport O2off Tune. 3" Full exhaust with 2 32" resonators and mufflers.
I have recently started putting premium Costco gas in the car. My friend who gets gas from the same spot is having fuel related issues. He drives an integra GSR . Not sure if this is a coincidence or it is bad costco gas causing this.
I stopped by Autozone and put a whole thing of fuel injector cleaner and octane boost with hydration eliminator in the car and drove it home for 10 miles. It didn't drive any better!
The car sounds and drives like a tractor and I dont wanna damage anything so you help is definitely appreciated.