r8f1k

On it

Bump

Working on my brother in laws 2008 1500 Silverado, 200,000 plus miles, 5.3L. Had a flashing check engine light, put a Snap-On Modis on it and it read a misfire cylinder 4, code PO300. Ok fine. My brother in law changed the spark plugs, new plug wires, new PCV. He said he swapped the #2 coil with the #4 coil to see if the problem moved. Nope. I did the same thing making sure good grounds, good pin contact, etc. No change. Used a spark tester to see if we have weak or irregular spark, all coils check good. I cleared all the codes via Modis and the check engine light went off, new code, MAF failure. Reset codes again, remove battery cable, reconnect, same code. MAF looked original, replaced, code gone, still runs like hell. Clear codes again, new codes. Now it says bank 1 sensor 1 and bank 1 sensor 2, failure. Is it O2 sensors that are causing all of this misfire? When you run vehicle data while engine running, #4 clearly has an issue. I don't think it is coil related, spark plug related, or wire related. Did GM step by step pin check on the #4 connector and coil, checks out fine. What the heck is going on?