adambraap

every odd cylinder misfires at idle all the way up and gets worse at 3500 rpm and starts spark knocking changed plugs wires checked coilpacks swaped o2 sensors pulled injectors out they all look fine any ideas would help

48fan

What's the year and engine model?

It may be that you have a carbon build up on your pistons, cylinders or both; as your compression increases so does heat in the cylinder, the carbon deposits can get extremely hot causing precombustion. The best way I know of to check and clean the pistons and cylinders is to pull the heads off and bar the engine till each piston is at Top Dead Center (TDC) then you can check the pistons for carbon deposits. If there is carbon you can remove it with chemicals and a wire brush. Just make sure not to get the flakes in between the piston and cylinder walls.

adambraap

2002 chevy silverado 5.3 74,000 miles

48fan

also another thing is oil getting into your cylinder. Check to see if you have oil on your spark plugs, you may have a blown head gasket.

adambraap

5 mechanics later i found out i had a plugged catalitic converter it was covered under gm's emission waranty