I have a 2002 LS. 4.3vortex. 140,000 miles. Blazer started running real rough at idle. Computer reads Number 6 cyc. misfire. Mechanic says compression is 75psi in that cylinder. Blazer runs worse on humid days.


I was told several things to check, including plug wires, plugs. Also told could be rings or valves. One mech. thinks it rings. Another says not likely. Blazer doesn't smoke.


I'm not sure if other cyl. were checked. Has anyone had this prob? Thanks for any info.

 

I had a valve that wasn't sealing. Loosen bolts on rocker arms and connect air hose to that cylinder. If you have air escaping, you have an intake or exhaust valve that is not sealing.

On mine it was #5. Idle was terrible and compression was much lower than the others. Replaced that head and it has been running great for 20,000 miles.