i have a 1999 f250 super duty with no power. bought it not running and took it to a mechanic to have the heads redone. after a couple grand it runs fine and will drive down the road ok but put a small trailer (2000 lbs) behind it and it will not go faster than 50 mph in second gear and will barely maintain speed in third gear.is there a transmission problem or did the head job get messed up? is it possible the timming chains are a link off. it does sound good at idle and reving it up.

 

I tow a 6500 lb travel trailer with my 5.4 F-150.

Similar thing. I could't hold speed on hills at all, acceleration was terrible.

Motor sounded terrible at idle.

Turned out to be a plugged catalytic converter on the drivers side.

Replaced the cat, now the truck pulls the trailer with more than enough power, it doesn't shift around or anything now.

IMHO, You may have a cat going down.

is there a CEL?

Thanks!

Jeremiah

 

cat conver was removed, new fuel filter , checked fuel pressure 47psi at rail and did not change problem.

 

Were the COP's replaced, have you pulled the plugs to make sure that they are all firing?

Thanks!

 

only one of the coils were replaced. is it possible to have a bad one and not get any kind of error code.

 

I ended up having to replace all my coil packs. Once one went bad they all followed suit within 2500 to 7000 miles later. I know you have 47 psi at the fuel rail, how about when it is under strain though. I towed a trailer to Florida, truck ran great before I put the trailer behind it. Half way there it was bogging down running like garbage. Ended up needing a new fuel pump. The old pump could not keep up with the added strain of towing a trailer.

 

i have check fuel pressure under load and it stayes the same. im going to buy all new coils soon. thanks everybody for the help and keep any ideas coming. this truck has been to three mechanics and no one can find a solution, so i guess im on my own.