Hello I have a 99 f150 with 4.2L with 100,000 miles I recently changed the oringinal plugs with bosch plugs at the same time I replaced the fuel filter and changed the oil and filter and the air filter. since then the truck has been down on power like I'm pulling a trailer when I'm not. And when I do pull a trailer it will barley reach 65 mph when before the tune up it would pull the same trailer 70 plus easily. Any suggestions would be great thanks. plugs are bosch super plus 7981.

 

Never done a fuel filter change on an F150, but those I have done were very specific on the orientation of the fuel filter. I was told that the filter is only designed to flow one way, and that putting it in backwards would cause all sorts of flow problems.

Maybe the filter's in backwards? That would restrict the fuel getting to the engine and cause lack of power, among other things. How does it run aside from being anemic? Misfiring? Trouble codes? Bogging under acceleration?

I'd get a fuel pressure gauge and check the pressure at the rail, and make sure it's getting enough gas!

 

if i remember correct, i have heard bad things about bosch plugs in fords, someone correct me if i am wrong.

 

You do remember correct, many people have had lots of problems with Bosch plugs.

But if the engine is not misfiring, and still starts fine, it's not going to be a plug problem. Sounds like when he gets into it, there isn't enough fuel getting to the motor. At least in my opinion.

Does it bog down when you put your foot into it?

 

AGreeing with the post above - I doubt the plugs are causing the problem, but...you never know.
I would suggest going back to Motorcraft plugs at the earliest convenience. Too many guys here over the years have run into problems with plugs other than Motorcraft.

I have changed fuel filters several times and honestly don't remember that you could put one in backwards. There is a flow dircetion arrow on the filter, so you should be able to check that.

You didn't get a rag or paper towel stuck in the air tube when you changed the air filter?

Keep is posted. I'd like to know what you find to be the problem.

 

Id bet its the sparkplugs. Ive heard of lot of people who used something other than OEM or the equivilent Autolite plugs and had problems.
Switch back to the OEM plugs and see what happens. Id bet it cures your problem.