What GPs did GM put in for 1999?

[AndyL]

Are my stock GPs the 60Gs?

[ucdavis]

I don't think so. I believe the orig were AC-11G.
You can tell easily, model number is stamped on collar. Use a 3/8" deep socket to remove one.

[AndyL]

Were they the ones that burned the tips off or swelled?

[john8662]

Nope, the Ac11G's were good plugs, just some say they were short lived. I have a set in my 6.2 with no problems, good starting plugs. These plugs won't swell like the AC9G's. But offer better starting than the 60G's. As long as they are still working good, leave em be!

[AC Bingel]

I just replaced my original glow plugs in my 99 Suburban (just turned 100,000 miles). They were the AC 11-G's. One was burnt out. I replaced them with the ones Kennedy sells. Seem to work just as well and are talked highly of on this site.

[ucdavis]

One caution, my rig was supposedly equipped w/11G's, but wasn't; I had 9Gs. Everything I had read said the 9Gs were discontinued B4 production date of my rig. Moral of the story is you have whatever plugs were used; check the model # stamped on one (the middle plugs on driver side are easy to get out for a check).

[damork]

ucdavis,
I have a 1995 too which came factory equipped with 9G's. I switched them out 100k ago with 60G's and still have them in it. I also found I needed a new relay which really made it start good - the relay it comes with doesn't seem to have heavy enough contacts in my opinion. A bigger relay seems to make sense, but I haven't tried that.

About the time I think the glow plugs are to blame, I end up getting a tank of good fuel and it starts the way it should.