2006 F150 5.4 100,000 + just tuned up new plugs [ that was fun! ] new gas filter,air filter ,oil&filter everything motorcraft [old plugs look normal.] After driving truck all day , sometimes at highway speeds you feel a slight skip engine seems to lose a little power. The check engine light will begin to flash. If you take it out of overdrive it straightens out.No codes except once it showed [misfire #4 cylinder] I checked everything out it seemed fine also it has never set that code again. Sometimes when all this occurs there will be a LOUD KNOCK! something like a diesel might make.Any help would be great Thanks.

 

At first I'd say possibly a Cam phaser... (diesel noise)

...but since you just completed all those PM related items, I'd start looking at a possibly damaged or a flakey connection on a COP?

 

Thanks for reply [what is cop] ? sorry this engine is new to me. If you are suggesting that I might have distured something, the engine was doing this before tune up. what is a Cam phaser and what is it's function and is it possible to repair or replace with out a bunch of tools? Thanks again.

 

COP= Coil On Plug