Codycody

Still have the misfire after multiple new plugs and coils. Anyone have an idea on how to diagnose what the issue is?

F150Torqued

Sounds like you may need to do a compression test and make sure that cylinder is 'breathing' properly. These engines can 'spit' roller followers out if a valve gets sticky and doesn't close firmly 'just once' sometime. It will still run with one intake valve not working - but not well. May have to remove valve cover to absolutely determine what's going on if compression test doesn't identify that one as being low.

A Power Balance test (XXX but I don't want you to have to go to a stealership to get that done) would show a weak cylinder under that condition.

Codycody

Yeah, I can do a compression test if that's what you're saying, but it was running perfectly before plugs and coils and now a misfire bouncing around between two cylinders. During the plug and coil change I had a bad valve?

F150Torqued

"During the plug and coil change I had a bad valve?" NO, but as a byproduct of a plug change --- a piece of carbon, or -very likely on this engine, a piece of ceramic from a plug if one has to be extracted with the Lisle tool, can get into the cylinder. Bounce around in there for a while and get lodged underneath a valve seat. Like I said, it only takes ONE revolution with a valve not seating and keeping valve spring pressure against the roller follower. THEY ARE ONLY kept in place by three point pressure between lash adjuster / cam lobe-to-roller / and roller follower-to-valve stem.

Codycody

None of the plugs had to be extracted. Although worn, they were all in one piece. I'll do the compression test and follow up with my findings. Thanks!

Codycody

Update!

We ground part of the center of the rounded off plug and used an ez out to get it out. Popped in a new plug, and the truck runs awesome! We are doing a phaser and timing chain job in 2 weekends!Thanks for all the help guys!

SilverSport

great news...

Bill