I have a 1998 F-150 with a 5.4 Tritan engine.
At the speed range of 35-45mph, the engine starts to lose power and hesitate. I have had new plugs, wires and spark plug boots replaced.

To my chagrine, this did not eliminate the problem.

I am going to have the fuel injection system get a thorough cleaning.

Anyone else have this problem and what did you do to fix it?

 

Maybe a coil breaking down under load?
Is it only speed related or could it be rpm or engine load related? What brand plugs did you use.

 

The issue is strictly speed-related.

I do not know what kind of plugs were used, they were installed by my mechanic.

 

I ask because I have read a few threads where our trucks have had issues with Bosch plugs in them.

Are you getting any SES light when this happens?

 

I think the 3 valve 5.4's have the problem with those plugs, not the 2 valve.

 

Nope, the are a problem in the 2v's too. Randam misfires, fouling, causing the engine to knock.......

 

I can check to see what type of plugs were used.
I do not get any SES warning lights when this hesitation occurs.

The truck was put on a diagnostic computer and nothing showed.