What codes are you getting?
I got "lean on bank 2" for a different vehicle. It had ~70k so I replaced the O2's, problem came back within a day. A few google clicks and I quickly realized it needed a new MAF sensor. From my reading, P0174 is most commonly bad/dirty MAF or a vacuum leak. Since this year 5.4 doesn't use a MAF, I'd start by looking for a vacuum leak.

 

^^^ Say what ???

BSB

 

Dang, I guess the MAF in my truck really isn't there! (One thing less to worry about).

- Jack

 

You can now worry about that thingy they put in the intake tube that substitutes for an MAF.

 

I did a quick look on rockauto and didn't see a MAF so I thought they went back to a speed density type system, guess I should have googled that first, excuse me while I remove the taste of sock from my mouth.

corrected:
From my reading, P0174 is most commonly bad/dirty MAF or a vacuum leak. I'd start by cleaning the MAF, then looking for a vacuum leak, then replacing the MAF.

better?

 

It's all good. Forgive me - I just couldn't resist (having been there myself and done that more times than I can remember. One I distinctly recall was talking about a collapsed lower radiator hose in a VW Beetle. I think it was glc that put me in my place on that one).

- Jack

 

My 05 XLT with the 5.4 recently has had #3 misfires replaced a coil pack 2 weeks ago. Today the check engine light came back on again had the code read another PO303 code. The plugs were changed at 131k truck now has 168k on it.

 

What brand COP did you use? What brand plugs do you have? Did you use dielectric grease? I'd be concerned about possibly a leaky fuel injector.

 

Had the same problem as you and did everything you did except change out the MAF.
in the end I found out it was the new motorcrap plugs I put in two was defective,so you might want to check that out.