Hello all hope everyone is having a good weekend. I need some help with my 2003 F150 SCrew 5.4l 4x4. The motor runs strong with no misses, stalling, etc. However, when leaving from a stop after the engine has warmed I have to almost floor it to get it to move at all. I haven't done any work on the engine recently.

The most recent repair was fixing a broken vacuum line, but that was a couple months ago. Normally when this happens I would suspect a vacuum leak, but my short term and long term fuel trims regularly operate well below 5%. There is no misfire, so I don't think coil packs are to blame either.

I am stumped! Other than this issues, the truck runs great. What are your thoughts on what is causing this?

 

Your story seems to be missing some stuff. How can it run strong if you have to floor it from a stop? Is the problem intermittent or does it happen every time the engine warms up? Does engine RPM increase while it's not moving? Has it ever run correctly? How long have you had it? Tell a better story, there might be clues.

If the throttle system is like mine it's a cable operated throttle blade. Completely mechanical. Engine speed is controlled by air flow. When the blade opens air enters and engine speed increases.

Kind of sounds like the transmission is not downshifting. Starting in a high gear. Or the torque converter is locked. You might try manually shifting to the lowest gear and see if there's a difference. Just spitballing.

 

Fuel filter.

 

Thanks. I am gonna give that a shot.

 

Good luck. If you meant fuel filter as the "shot".

 

Lol. I definitely did! I replaced it about 3 years ago, so may be time for a new one.

 

Not seeing how the symptoms indicate lack of fuel supply. Your fuel trims would rise. Fuel trims can tell you a lot about what's happening in the engine. Trust the data.

 

That does make sense to me. I was also thinking thw fan clutch may be to blame since it doesn't seem like the fan ever lets up.

 

Yea they get dirty pretty quick. Change it every 9000 miles and you be alright. That data means nothing AFA a bad filter as it could plug intermittently. Start with the simple stuff....fuel first.

 

Thanks! Will be doing this first thing tomorrow!

Gotta get this fixed! Got stuck way too much on this year's offroad trip!