I have a 99 F150 with the 5.4L, 50000 mi. The truck seems to bog down when under a med. to hard acceleration, then catches up and runs fine. It seems to only happen after it has warmed up to mormal temp. Checked plugs, changed fuel filter, everything looked good. Tranny fluid changed at 40000. I also have not had the check engine light on at all.
???Anyone have any ideas???

 

Chillybone,
Welcome to FTE! Glad you found us and hope we can help.
I only have a guess....fuel pump. I have heard of a few failing but I have never had the problem. Maybe fuel injectors.
Somebody will probably come along that will have a better idea.
Again, welcome to FTE.

 

Try cleaning the mass-airflow sensor. When they get dirty, they tend to lean out the engine.

Jimmy

 

I will sugest to find a good scanner like Autoxray 6000 and look for operating conditions after warm up. I have found that sometimes marginal oxygen sensors, air flow meter, etc. can cause operating malfunction without activating the check engine light.

Good Luck!
Ponsik

 

chillybone:

How's that air filter looking? Or more like, when was that air filter last changed???
-hooD