This was not an easy fix. Hats off to my mechanic.
157,000 miles mix of highway and local. Got the dreaded P0300 running down the interstate light throttle. Blinking CEL went out under load or coasting. For the CEL to be on & flashing, had to be steady / light throttle. My mechanic's scanner displayed random misfires on all cylinders, but more so from #s 1 & 6. All sensors checked out ok. Smoked the intake...no leaks. Cleaned the injectors, replaced the plugs, checked coil packs, grounds, & plug wires. Nothing was making sense, so he put in a reman ECM along with all the updates. Still got the P0300. With the help of his friend (who makes his living traveling to shops diagnosing), they found the timing chain had excessive slop. Super loose. The crankshaft turned 40 degrees before the chain started to turn the cam. Under steady/light throttle, the crank and cam were just rockin' & rollin' (floating) back and forth causing the code.
New timing chain fixed it. Runs as good as new now. I didn't realize the slow degradation of performance until the new chain went in.
Side note......... After the chain replacement, no more P0300, but then got a P0101 (MAF sensor) code. WTF ??. I replaced the MAF with a new Delphi one & still had P0101. No snorkel leaks. My mechanic put back in the original ECM and no more MAF P0101 code. I hate aftermarket parts. Give me genuine GM any day.
157,000 miles mix of highway and local. Got the dreaded P0300 running down the interstate light throttle. Blinking CEL went out under load or coasting. For the CEL to be on & flashing, had to be steady / light throttle. My mechanic's scanner displayed random misfires on all cylinders, but more so from #s 1 & 6. All sensors checked out ok. Smoked the intake...no leaks. Cleaned the injectors, replaced the plugs, checked coil packs, grounds, & plug wires. Nothing was making sense, so he put in a reman ECM along with all the updates. Still got the P0300. With the help of his friend (who makes his living traveling to shops diagnosing), they found the timing chain had excessive slop. Super loose. The crankshaft turned 40 degrees before the chain started to turn the cam. Under steady/light throttle, the crank and cam were just rockin' & rollin' (floating) back and forth causing the code.
New timing chain fixed it. Runs as good as new now. I didn't realize the slow degradation of performance until the new chain went in.
Side note......... After the chain replacement, no more P0300, but then got a P0101 (MAF sensor) code. WTF ??. I replaced the MAF with a new Delphi one & still had P0101. No snorkel leaks. My mechanic put back in the original ECM and no more MAF P0101 code. I hate aftermarket parts. Give me genuine GM any day.