In my quest to take care of the many known and unknown issues with my truck i bought used, changing plugs and wires was definitely on the list. i thought ...

In my quest to take care of the many known and unknown issues with my truck i bought used, changing plugs and wires was definitely on the list. i thought that i had read somewhere previously that new (GM) plugs come out of the box already gapped and ready to go. i couldn't recall for certain so i asked the parts guy if he knew what it was and he told me .040. so when i changed the plugs, i 're-gapped' them all to .040, and have since read in the owners manual that the gap is .060... yep, silly me for not looking there first, but that's a mute point right now. my only question is, is there any negative issues to having a smaller gap or is it 'imperative' that i re-gap them as soon as possible. i will say that error or not, because of the smaller gap (i guess) my mileage has improved, so unless there is a technical reason why i shouldn't leave them at .040, then i am inclined to leave them as they are...

there was an update to the factory gap setting and yes i do believe it is .040

You did a pretty reasonable job of answering your own question. The only thing you don't know for sure is whether the mileage would be even better with a larger gap with the new plugs.

If they're not too hard to remove, you could try a larger gap and see what happens WRT/mileage. If nothing else, it's a useful experiment that might help others here. FWIW, it looks like newer engines specify .040"

If I were in this situation, and being the lazy slacker I am, they'd stay at .040". Besides, as they erode with use, the gap is going to increase naturally.

srr2 wrote:If I were in this situation, and being the lazy slacker I am, they'd stay at .040". Besides, as they erode with use, the gap is going to increase naturally.

I'm with you on this one, cuz i really don't have time to do it over, not that it's hard. i would rather change those plugs than the plugs in my 'Z' any day... so the play stands as called. thanks for the replies...

Did you have to change them much? 0.40 to 0.60 is a pretty decent amount of change. If they came pre-gapped, and you did not have to make much if any change to get to 0.40, you know you got it right.

For iridium plugs, they do not recommend changing the gap, as the electrode is very brittle and easily damaged.

yea, i know it's a decent amount, but i was careful in doing so... it's running fine, so if the electrode(s) end up going bad, won't be that big of a deal to do it again. but as i stated in the original post, i thought they were pre-gapped, and that would have been at .060. i just couldn't recall that at the time and asked the parts guy who looked it up and told me .040. adams99z71 also said there may have been an update... so i really don't know. i gapped them to what i believed to be correct at the time, and have no issues with it, so gonna roll with it for now. i had started this post cuz i just didn't know if i should expect any issues, or if an improper gap was going to cause any performance issues. if that were the case, then i would have corrected it. i do know that my mileage has improved with a smaller gap... the part number plug i got is 12621258, so if any of the GM peeps out there can confirm or deny the gap, or any tsb for it, then maybe that'll shed some light on the subject. is that part number an iridium plug anyways?

I replaced the plugs and wires on my 02 Silverado 5.3 at 150,000 miles and Noticed no difference in milage and performance, Sort of made me wonder if it was worth it!. Don't know what the gap of the old plugs was, but they were wide.....................