I don't know if I believe their troubleshooting, but the dealer service shop claimed they "inspected" the coil pack and that they "removed and inspected it", but they claim it was a bad wire, saying the misfire moved when they moved the wire and advised removing the plug boot heat shields, which I did. I have heard that testing a coil pack will not necessarily indicate if it is bad/failing/intermittent, anyone know? I am thinking this coil is the problem.

So I replaced plugs & wires, threw in more fuel system cleaner in the gas, and I still have a P0305 Cylinder 5 Misfire - what would you try next?

TIA

 

The usual suspects in a single cylinder misfire:
Spark plug
Spark plug wire
Coil firing that cylinder
Ignition module (seldom)
Fuel injector not working properly
Mechanical problems causing low compression on that cylinder

 

Thanks. Do you have some examples of the types of mechanical problems causing compression problems besides gaskets?

 

I don't know but looks like misfiring is pretty common on the V6. I just installed a donor engine with new plugs and wires. It ran fine the first day and the second it misfiring and SES light is flashing. I have not had it scanned yet because I can hear a vac leak at the EGR valve. I don't know if I crimped the EGR tube when installing engine or if the EGR valve is what is leaking. I do know that it is loose from the mount. I am hoping this is what is causing my misfiring.

 

Valves sticking open, piston rings blowing by

 

For a single cylinder misfire, how could a coil pack be the problem since it fires two cylinders and shares a common ground? If the coil was bad, wouldn't TWO cylinders be misfiring?!

 

The coil normally has two paths to ground throgh the spark plugs. 1/2 of the output side of the coil can go bad and the other side can still have a good path to ground through the spark plug and still be able to fire the plug, while the other side is dead.

 

Thanks for a good answer, as usual. I had been suggesting to the Chevrolet shop that coil packs tend to be common failure points for this type of problem largely based on the posts I've read in these forums. But the answer of sharing a common ground and that multiple cylinders should be misfiring is a coil is bad is what the SHOP advised me.

The shop thinks the injector is the culprit we'll see soon enough -- I hope I don't find out that the shop techs don't know as much as they let-on...

I think I need to see a break-away of a coil pack, to help understand the explanation and better see how they work. Anyone have one? I thought they are mostly just coiled wire...

 

I would swap the coils around and see if it follows. If it does, likely the coil. If it doesn't follow, plugs, wires, or ICM.

 

Of course the injector replacement did not fix the cylinder 5 P0305 misfire, it's still totally repeatable at WOT. I think it's the coil -- these shops don't understand how this tech works, or their just trying to milk an issue for all it's worth. :-(