Ok...this is pretty baffling....a buddy of mine bought a 91 F150 ext. can 4x4..high mileage but a nice truck for what he paid..he jus wanted something to beat around in for the winter..and to tow his Stang....anyway...he decided to give it a tune up...plugs..wires...etc...he went to change the plugs...the plugs they gave him would not start,,,,so..like anyone else..he thought they gave him the wrong plug...nope..they were right....long story short..the only plug he could find that would fit in the hole and start, is a plug for a Lincoln V6....as im sure most know the threads are recessed into the head a little...none of the "right" plugs would even go in the hole...to big of diameter..the V6 plug fit.....anyone have ANY ideas as to whats going on with this?????

Sorry its such a long post....

What kind of motor does he have... EFI 4.9l straight six?

Damn..im an idiot..I thought i put it in there.......its a 302..EFI

I did a tune up on my neighbors 91or 90 bronco with the 302 and it took off the shelf plugs, kinda weird though.