ok i am a 5.0 mustang guy, so this modular stuff is all wierd to me!

ok so we have this 99 expedition with the 5.4, 2wd XLT

it misfires really bad, which causes a bad stumbling problem on acceleration. of course my dad has lived with this for over a month, and now its gotten so worse that it idles rough and dies if you don't give it some gas and use both brake and gas to get it going.

i've tried replacing the plugs on this beast before and its not anything like the 5.0's what the hell is up with this thing? and suggestions on replaceing the spark plugs? also anything else that could cause this behavior on his 5.4?

 

Welcome to the forum. If you go to the 97-03 forum, there is great info on spark plug changing. They are a pain to change that's for sure.

Is the Check engine light on? It sounds like probably a bad COP (Coil On Plug)
Get the computer scanned, it will tell you which cylinder is missing. Check for a small antifreeze leak at the heater hose fittings above the # 3 & 4 cyl's. If water gets into the plug pockets, it will short them out.
It wouldn't hurt to go ahead and clean the MAF and check the PCV hose assembly for cracks. Especially the elbow behind the intake manifold.