Most spark plugs come with the correct gap between center electrode and ground electrode, key word is "most"
Rangers tend to eat non-motorcraft spark plugs, so if possible get Motorcraft plugs
Also I put a can of Seafoam gas treatment in the tank once a year, $7-$10, it keeps my 4.0l's injectors clean.
I used to say BS on gas treatment(pre-fuel injection days).......until I started getting missing, random though not specific to a cylinder, for what it's worth my first can cleared it up, that was after me spending $$ on new plugs and wires that were less than a year old, lol.
315k miles on the original injectors now
You probably need the new plugs, wires are up to you, but don't forget the injectors, in your engine the injectors are sequential(only the cylinder with open intake valve is gets fuel), so dirty injector can cause a cylinder specific miss.
And for a bit of bad news.........I think the 2003 3.0l was on the list(TSB) for bad valve seats in the head, they would come loose and float causing a steady miss but it would come and go, I think it was the exhaust valves that were effected.
Last edited by RonD; 01-11-2014 at 06:41 PM.