The plug blew out of #4 about 2,000 miles ago and was helicoiled. Now it is missfiring. I have changed the COP and the injector. Cant seem to get plug out. but I do not hear any blow by the plug like it is loose. I have no idea what to do next.

 

Did misfire started after 2000K miles? Or right after plug repair?
Check connector on that COP.
Might be different cylinder?
Run scanner on it and check for codes,first.

 

Hope your was not like mine. #4 blew......shop repaired while I was on vacation. Still had a misfire. Got it home....pulled the plug and found out they lock-tited the insert to the plug and never-seized the insert in the head. Now I have a burnt valve which everybody has told me that if they did not make sure the valves were closed on that cylinder when doing the insert....a small piece of aluminum could have been trapped between the valve and valve seat. Only gonna cost about 2K to get the head pulled and a new valve installed.

 

The truck ran great for 2,000. I was climbing a steep grade a few weeks ago, and motor starting pinging like a low octane ping. Then missfire started. I was afraid of junk in valves from installation too. I havent check yet for proper spark yet, next on list.

 

Oh codes did identify #4 as a miss fire.

 

Same problem, mine made it 16k miles then carbon built up on the insert and cracked valve. Had head pulled and insert installed. Now 4k miles later it's back at the shop with another miss, all plugs and boots are new 4k miles ago. This is one overated tempermental POS and I could not recommend anyone buying a V10. If interested proceed with caution as this has been the most expensive 21k miles in my 30 years of driving.

 

Just checked both COP and injector and both have proper electric profiles. Pulled plug and the helicoil came out with it. The electoid on plug was destroyed! Melted off! Put new plug and new insert in and started it. Blew plug/insert straight out breaking new COP. Still ran with a missfire with new plug in before it blew out.

 

Mine ended up beeing #10 cylinder injector harness had bad connection.Plastic tab broke off, it is now tie wrapped.

 

Most of my injector clips are broke and zip tied.

 

Well, put new plug/insert back in with JB weld with hopes to remove plug and test for compression. Let set for a couple days put COP back on and fired it up. Everything stayed in place and runs like new, well on all 10 anyhow. Ran down road and back so far no problems. Oh well couldnt hurt it anymore. We will see. Anybody want to buy a great running Excursion???