Hi I am brand new here so forgive me for any noob mistakes.

To start off we are dealing with a 2000- 5.4 -4x4 with about 160k on it. About 3 months ago I ran into the dreaded COP misfire issue and broke down and spent an afternoon changing all of them. I got all 8 packs for right around $200 from a parts store online and got platinum plugs from Autozone. Ran like a dream after doing that. I noticed when changing the plugs though that one of them was oil fouled and thought it could be from it just not firing because of the COP. PCV valve has been changed also.

Here we are about 6 months later and misfiring has returned just as bad if not worse than before. It does burn some oil from time to time but not consistently. Also I have noticed before that on start up it would puff some blueish smoke but that was it. CEL is on and the code is for a DPFE sensor and have replaced it and cleared the code but it returned almost instantly. I have read that it could have something do do with carbon buildup on intake.

So with all that said I can get to my real questions. I have concerns it could be valves (guide, seals, ect.) I know this is very possible but is this common or am I way off base? I steer towards valves because of the smoke on startup like maybe a stuck valve. I do not believe it to be rings at this point because without the misfire I have plenty of power left. I haven't had time yet to do compression but will eventually.

I am an excellent parts changer and wrench turner but once you get into internal parts I'm very under experienced and lack the knowledge. Need some direction!

 

Pull that plug again and replace it with another new one maybe a range hotter. If it is oil soaked with carbon you got your answer. It's probably an oil ring. If it runs sweet you got another 6 months to go. You know not to run it out of oil.