I just finished the dreaded plug and wire change on my 4.6. All went well, and it only took about 2.5 hours to do. This was my first time to do it. The stock plugs had about 60000 miles on them. When i checked the gap of the old plugs it was around .045 on all of them. My new plugs are gapped to .054 like what the sticker under the hood calls for.

Does anybody know why the factory plugs would have such a small gap? The truck was running fine other than the 10MPG i was getting. Would this have an effect on it?

 

Dunno why you had smaller gaps, but the gaps on my old plugs were all OVER .060 and this was at about 62,000 miles.

Actually, a larger gap is good for the spark, but it's harder on the ignition system, as the coil has to work just that much harder to bridge the larger gap.

Having a smaller gap could cause "less" of a spark I suppose, but you'd think that a "spark is a spark", right???

Doesn't take much of a spark to light my propane barbeque, that's for sure!

 

I supposed a smaller gap may have a lsightly pre-mature spark resulting is less than ideal combustion, more wasted fuel, and worse economy. My plugs were at about .060-.065" at 59k when I replaced them. New ones went in at .054".

 

yeah the worst part is last year when i bought the truck i had a miss fire on cyl#2. The dealer i bought it from said they replaced the plug wire (cause of the problem) and all of the plugs. I was skeptical but didn't bother changing them until now. The plugs that came out had to be the originals. They were worn and rusted around the nut. Needless to say i don't go there anymore.