New ac delco 41-993 spark plugs , No start

[Frank Enstein]

Small Block Vortec heads take a .708" reach, taper seat, 5/8" hex spark plug.

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[L31MaxExpress]

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.

Correct reach on a 96-02 Vortec 4.3, 5.0 or 5.7 is 0.750".

 

[mattillac]

I installed 41-993 plugs a couple of years ago in my 1999 5.7 vin R and remember having to adjust the gap for all eight of them.

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IIRC, had to decrease the gap, but it's been a while.
Other than that, haven't really had any trouble with them.

 

[1998_K1500_Sub]

You might want to check the gap on those plugs and see if it's .060; reportedly that's what they're supposed to be out-of-the-box. Stranger things have happened...

You can always connect a wire directly from the coil to one of those new plugs, then ground the plug to the engine somewhere (I've used a rubber band to strap a plug to, e.g., to a stud or some such thing that has a solid electrical connection to the block) and have someone crank the engine while you watch for spark. Optional: You might want to pull the fuel pump fuse beforehand so you're not pumping fuel into the engine while cranking.