New ac delco 41-993 spark plugs , No start

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wirlybird

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Compare the '993s to the old plugs. Is the threaded portion longer?

'993s are probably not the correct plugs. I bet the reach is too long.

'Course, you could have told us what engine the truck has...

Check with AC-Delco. Could be you're not supposed to re-gap the plugs. Problems with breaking-off the li'l Platinum nubs, or bending the thin center electrode.
He has the 5.7. The 993 is the Iridium plug we have talked about that supposedly does not fit the 7.4 Vortec but does fit the 5.7. Go figure!
It does have a longer reach, which I think you pointed out to me, than some of the other plugs for that engine.
 

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Schurkey

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I looked on the AC-Delco web site. I was wrong--the reach is not .900, it's .980.

They claim that plug is correct for a "VIN R" Vortec 5.7L; but then they also say it's got a gasket seat instead of a taper seat. I don't think those boneheads know what they're talking about.

I would damned sure be measuring the amount of thread-depth in the spark plug hole, to make sure you don't have a quarter-inch of threads sticking out into the combustion chamber leading to detonation, and difficult plug removal once they carbon-up.

AC also specifically says "don't re-gap".
 

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Whatever OTHER plugs the AC-Delco site recommends.

Unless you've verified that you've got an inch of thread-depth in your cylinder head. Based on the other choices, I'd guess you've got enough threads for a .680-ish reach plug. But I haven't done thread-depth measurements.

I really believe that the '993 plugs are listed for that engine by mistake.

As I said in the other spark plug thread, the '993s are what fits my '92--'93 Lumina 3.4L, aluminum heads with long thread engagement to make up for the reduced structural strength compared to iron threads.

According to the AC-Delco "Buyer's Guide", they're listed for my Luminas and similar 3.4L DOHC vehicles, along with 4.3L V-6, 5.0L and 5.7L V-8. But I don't know how they can be right for the iron-head engines if the plug threads in those heads aren't long enough.
 
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