So I figured after changing the oil in my 08 Expedition that I just bought I would check to see if it had the redesigned head and if the plugs came out easy (unlike my 04 F150 had). First plug came out no problem, but had lots of carbon on the end of the plug. Oh, about 55k miles on it.

I figured I would clean off the carbon and put some anitseize on them any way. Did the drivers side, flashed it up and now a bad misfire. WTF? I took all the plugs out and cleaned off the antiseize and no change. I put very little on the plugs to begin with. Ran the engine for a few minutes thinking it would clean anything that might be in there away, but no, now a check engine light.

Obviously not gas, everything worked completely fine and all connections are made. I can smell gas in the exhaust, so I know the injector is working.

Stumped, but I am going to get a couple of plugs and replace a couple that seem to not work.

Could it be the COPs? They came out very easy.

Lets just say the wife is not too pleased that she is driving the Mustang to get the kids to school today.

 

If the boots from the COPs to the plugs are brown, you have the redesigned heads, if black the problem plugs. Sounds as if you got antisieze on a plug tip, maybe. Could be that you are shorting out a COP. Did you use dielectric grease on the boots?

 

Don't mess with the old plugs. Get a new set and install them properly, and reinstall the cops properly. If they are the old style plugs with the extended ground sleeve, you put high temp nickel antiseize on the sleeve ONLY - keep it away from the tips and the threads. The cops need dielectric grease inside the boots - do not overdo it and avoid getting grease on the contact spring.

If you got a CEL, read the codes.

 

Turns out the plugs were just plain worn out. The gap was huge from the tip and the ground part being eroded from the spark. Threw a new set in and blam, runs fine and the check engine light went away. Now time to replace the other side.

The tips of the the old plugs had no antiseize on them but still were obviously fouling. At least now the wife is happy to have her grocery getter back.