I just replaced the spark plugs on my 98 f150, and since then the truck will sputter and lag when you change gears. I pulled out all the spark plugs and replaced them with new ones, only to have the same results. Any ideas on what the next step would be?

 

air filter maybe. fuel pressure. timing. don't have any engine lights on? also double check the wires one crossed wire can give you this kind a trouble

 

You didn't mention it , but did you gap the plugs to the correct gap?
I believe timing is not adjustable on your vehicle.
In the process of replacing the plugs did you have to remove the air filter assy to get at everything? If so, check all the wires that may have been disturbed like intake air temp sensor etc. If you didn't have the problem before changing the plugs is a good bet you may have either overlooked something or disturbed something.

 

I forgot to mention , I did read on this forum somwhere that a problem existed with one of the valve rockers under the valve cover. If you suspect a compression problem and can determine which bank, you might remove the valve cover and confirm that there is no problem with one of the rockers thereby causing a possible compression problem. If this is the case , catching it before it holds a valve down and gets hit by the piston could save you some grief. Hope your problems are small and easily corrected.

 

Why did you change the plugs? and is it a v6 or v8 what engine because there are different problems for both and the are different style engines. if it is a 4.6 or 5.4 and you did it hot there can be a multitude of problems, like crosstheaded plug holes torn boots and its jumping spark or a coil is bad and only works ok at low speed opperation. but if power is there after the sputter then check the coils alone and the gap, oh and a side note only pull spark plugs out of an sohc ford when the engine is dead cold, things can get bad really quick and you would even realize it.

 

Thanks for the help guys. I'm gonna take it to the shop and have them look into it more. I've checked what you said but can't find the problem. Wish me luck