Hi. I have a 2000 GMC Sierra 5.3 and only 5 cylinders are firing. Iv checked the spark plugs, coil, plugs wires, and even wire harness going to coils. Those are good. So what else can cause the 3 cylinders to misfire? Thanx
Is the check engine light on because that should help narrow your issues down? The problem is it could be all kinds of things besides the obvious ones you've already checked. Here's a link that explains the myriad of causes that might be the reason for your issues.