Matticus06

Hey guys,

I know there is a thread on this page about "stumble/misfire" but it hasn't really helped me so sorry in advance.

I did a search and found so many conflicting opinions that I'm flabbergasted . MY '06 F150 5.4 w/ 54k miles hesitates around the 3500-4500rpm range ONLY. Above or below those rpms the motor runs fantastic. There is no struggle going up a hill or while cruising, it's only when I give it 3/4 to full throttle. I haven't noticed any strange sounds nor has my mpg been effected.

No CEL's, absolutely no rust on the frame so I doubt it is the DFPM. I am leaning towards it being a spark plug issue (which I believe are the originals) or possibly the COPs.

Does anyone have a suggestion to which would most likely be the cause of this hesitation/misfire?

Thanks for your time!
-Matt

Mod (Ret.)

Sounds like a cam or cam phaser issue to me.

nrivera04

My high rpm misfire was caused by a seized cam follower on the pass side that scored the cam lobe. I had no CELs or other obvious issues and it ran fine as long as you weren't above 2800+ rpms. I hope this isn't your issue cause it's a pricey one.