I'll pull one of the plugs and see exactly which plugs I put in it. If they're wrong, I'll swap them out and go from there.

 

 

Plugs are Champion RC12MCC4 plugs. However, the current gap on the one I pulled was a little over .060. Any idea why they're wearing out so fast? They have less than 10k miles on them. They were gapped at .040 when they were installed.

 

I know this thread is a couple of years old. Any resolution for this problem? I have a similar issue with my 4.7L. I'd rather change plugs than a cat...and I'm pretty sure that the engine has platinum plugs in it.

 

For these trucks, they prefer copper. I've read that a lot of people in this forum have had issues with platinum plugs.

 

Thanks for the reply. I've got a high mileage engine - nearly 240K miles, but the top end was redone around 120K miles due to a dropped valve seat. I was thinking that it was worn out, but compression seems ok for it's age - all cylinders close to 120 psi (after cranking 10 or 12 revolutions). The engine runs smooth otherwise. No misfires, no check engine light. Just extremely low on power. With a manual tranny, I have to shift down when going up a slight grade on the freeway, or against a stiff wind. Ordering some RC12MCC4 Champions now...hopefully they'll make a difference. I haven't checked the fuel pressure or pre/post cat pressures yet.