spark plugs

[MT-2500]

Originally Posted by cf1

well if i got 120,000 out of these delco, why not put the same number ac delco back in. im happy with the results.. thanks guys..

That is your choice.
But Gm has a lot of updated and improved spark plug no. and gaps on a lot of there engines and for the best most of the time.
Like they say best to go by the good book.
Good luck with them.

Did the new AC delco spark book show a change from your OEM plugs or still the same no. and also gap.?

[Ol'Jim]

I am changing the plugs on my 2002 Silvy HD 6.0, and since I have put 93,000 miles on this set, I figured I would replace them with whatever came out. Turns out AC/Delco plug and the only marking on it is "12". (And "Made in USA"). Nothing else anywhere. I can't find the AC #12 plug at any of the local parts stores, or the Autozone and O'Reilly websites. The show a P/N 41-110, is that that the same? Crazy thing is, the owners manual specifies only 2 plugs, an NGK P/N, and a Denso P/N. (Why only 2 Japanese plugs and no GM/AC Delco???). Anyway, the plug I pulled looks perfect, not too hot or cold. May even be the originals, (Truck had 97K on it when I bought it, now at 190,000). Gap is worn very wide, .100", still running good, with occasional miss at idle. So where do I get an AC/Delco 12, or does anyone have a cross-reference to another P/N? Definitely gonna stick with a GM/AC/Delco plug, I'd be a fool not to, in this case.

[Ol'Jim]

Interesting, the 93,000 mile plugs I removed from my truck are the "cheapie" AC/Delco Rapid-Fire plugs, $2.99 each. They are not on the list of recommended replacements, so I went with the (Ouch!) $7.09 each AC/Delco Irridium plugs listed as the GM replacement by several sites. They do have a 100,000 mile warranty on them. Also, as I pulled the first plug, the wire broke, leaving the terminal on the plug. The wires have those metal shells surrounding the plug boot, so there is nothing else you can pull on, other than the metal or the wire. I twisted it first, to break the boot loose from the plug insulator, I don't know what else I could have done to avoid breaking the wire. Maybe after 190,000 miles, they are just deteriorated to the point where it's inevitable... Anyway, replacement wires are very expensive also - $49 for the set. So a "routine" plug & wire change cost $115! Hopefully they will all last another 100K miles. The replacement wires were the "cheapie" house brand at O'Reilly, (Opti-Spark). At least they are lifetime warranty, and made in USA.
Will post an update when the job is done, hoping this will eliminate the "Service Engine Soon" light, so I can pass the annual Texas inspection and get my registration renewed. (The code scanner at AutoZone said "intermittent ignition miss", and recommended about 10 different things to change, plugs was 1st on list.

[MT-2500]

Originally Posted by Ol'Jim

I am changing the plugs on my 2002 Silvy HD 6.0, and since I have put 93,000 miles on this set, I figured I would replace them with whatever came out. Turns out AC/Delco plug and the only marking on it is "12". (And "Made in USA"). Nothing else anywhere. I can't find the AC #12 plug at any of the local parts stores, or the Autozone and O'Reilly websites. The show a P/N 41-110, is that that the same? Crazy thing is, the owners manual specifies only 2 plugs, an NGK P/N, and a Denso P/N. (Why only 2 Japanese plugs and no GM/AC Delco???). Anyway, the plug I pulled looks perfect, not too hot or cold. May even be the originals, (Truck had 97K on it when I bought it, now at 190,000). Gap is worn very wide, .100", still running good, with occasional miss at idle. So where do I get an AC/Delco 12, or does anyone have a cross-reference to another P/N? Definitely gonna stick with a GM/AC/Delco plug, I'd be a fool not to, in this case.

Someone before you changed the plugs to no 12 rapid fire plugs.

I show replacement plugs for it are AC 41-985 at .040 gap

[j cAT]

first post the DTC check engine failure codes ALL...

I agree with MT 2500 that the 41-985 ac delco irridium plugs are what is called for with the 2500HD 6.0l engine..

my 1500 5.3L engine uses the 41-110 iridium...

It you have the po300 code this can be many things..with all those miles check the fuel pressure with a pressure guage..low fuel pressure will do this ...as well as other items..make sure the plug wire resistance is checked on plug replacement..spark plugs should be replaced at 50,ooomi. use dielectric grease in the boot ends..this aids in removal and keeps water out which reduces the wires being damaged. those plugs you need are about a dollar more ..

[Ol'Jim]

The latest AC Delco Spark Plug book I could find, (2010), now shows the 41-110 Irridium as being the correct plug for the 6.0 engine, using a .040 gap.

The air cleaner decal on truck says .060 gap, but I went with the .040 recommended in the book. The plugs were apparently pre-gapped by the factory at .040, but I checked them all VERY CAREFULLY with a feeler gauge, using .039 as a "go", since .040 was somewhat snug, and I didn't want to damage the fragile-looking electrodes. All were precisely there.

Replaced all the plug wires as well. Truck starts quickly, idles beautifully, seems much more responsive off idle, and no more "Service Engine Soon" light. (Yes, it was PO300 DTC).

Thanks Guys!

[MT-2500]

Originally Posted by Ol'Jim

The latest AC Delco Spark Plug book I could find, (2010), now shows the 41-110 Irridium as being the correct plug for the 6.0 engine, using a .040 gap.

The air cleaner decal on truck says .060 gap, but I went with the .040 recommended in the book. The plugs were apparently pre-gapped by the factory at .040, but I checked them all VERY CAREFULLY with a feeler gauge, using .039 as a "go", since .040 was somewhat snug, and I didn't want to damage the fragile-looking electrodes. All were precisely there.

Replaced all the plug wires as well. Truck starts quickly, idles beautifully, seems much more responsive off idle, and no more "Service Engine Soon" light. (Yes, it was PO300 DTC).

Thanks Guys!

You are welcome.

Right on with what the newest AC Delco plug book calls for.
And never try to reset the gap.
Or use old specs off of decal
If the gap is not right pitch them back and get some that are right.
Good Luck