Lsxk5

2000 silverado, lq9, stock bore/stroke fresh rebuild. TSP 228R cam, ls7 lifters, TBSS intake, Holley sniper 92mm tb, 42lb bosch injectors. Headers, 3000 stahl. Stock coil packs. Dyno tuned, 355 rwhp. Develops a slight miss between 3000 and 6000 rpm. More of a "pop" sound. Had it back to the tunner, says it's a mis-fire on the drivers side. Could it be a bad coil pack? Any help appreciated

RockinWs6

Weak valve spring or cracked?

R6cowboy

iTrader: (3)

This sounds exactly like a mis-fire I had in the past, from 3000 rpm up. I originally thought it was a bad plug or coil, but ended up being a broke intake valve spring. Pop the valve cover and take a gander.

RevGTO

iTrader: (12)

I went through hell recently trying to chase down a hi-rpm backfire condition after a rocker arm install. After sorting through every possible mechanical theory for the problem, it turned out to be the brand new MSD plug wires I had put on it.

Very frustrating as my old MSD set was 10 years old with 95k and worked perfectly when I pulled them.

A good scanner will identify the cylinder(s) where the misfire is occurring. We finally solved the puzzle of my misfires by identifying the bad cylinders and then swapping the plug wires around. Sure enough, the misfires followed the wires.

RockinWs6

I had worn cam lobs cause this type of thing too. Cylinder pressure starts to build because the exhaust valve isn't opening enough and pushes back into the intake.

Weak cracked or broken springs can let the intake valve hang a bit and it will back fire.