Are the spark plugs different on the left and right side? I know thats a stupid question, but I just talked to my dad and he said thats what the manual and Popular Mechanics said. It is a 99 4x4 5.4 v8.

I have an F150 with the 5.4 and they are the same in it.

 

They aren't different.

 

I have a copy of the book.

Cyl 1,2,3 & 4 have a "PG" suffix
Cyl 5,6,7 & 8 have a "P" suffix.

It said if a plug is pulled it must reinstalled in the same cylinder. If a plug needs replaced, use only plugs with the same service part number suffix letter shown on the engine decal.


Page 190

 

I read alldata, and called ford. They are the same

 

From the factory, they were different. Replacements are the same part for both sides. Nothing wrong.... Ford just tried to save a buck or two by running a cheaper plug in one side. The figured that since one side fires under negative polarity, the electrode wear wouldn't be as great, so they didn't need a PT coating on one of 'em. It probably saved them a nickle per plug.... times four plugs per truck, times 900,000 trucks per year, times 7 years..... you get the picture.

Replace them with the recommended plug and they'll be fine.

-Joe