Spark plugs ignition coil

I would replace all 8. If a couple are bad, the rest aren't far behind.

How many miles on this vehicle? I would try just replacing the spark plugs and I would change all 8 of them out. If you end up having a bad coil or 2 then I would replace all 8 of those as well. When purchasing coils it is best to stick with Motorcraft coils from Ford as they are far more dependable than some of the aftermarket crap that is sold at the parts stores. Ford Motorcraft coils can be ordered on line as well as from www.tascaford.com at the discounted price of $48.33 each plus freight.

Also could be dirty or clogged fuel injectors or fuel system including low fuel pressure or clogged fuel filter, or low compression including blown head gaskets or burned valves or bad rings. As said above buy Ford Motorcraft, as the other coils are junk.

You really want all spark plugs to be in the same condition.