New ac delco 41-993 spark plugs , No start

[mkcustoms881]

So today I installed new ac delco 41-993 spark plugs on my 1998 silverado and would not start , so I pulled them.back out there was 6 plugs that still looked new and 2 that are completely black what went wrong ?

 

[wirlybird]

What engine? Just curious on that.
My first guess is the plug wires are out of order. I'd verify the firing order/plug wire order from cap to cylinder first.

 

[mkcustoms881]

5.7 , funny thing is I put the old plugs back in and it fired up

 

[mkcustoms881]

I was thinking maybe something wrong with the cap and rotor but why does it start with ****** old plugs

 

[wirlybird]

See if you can check the gap between the old plug and the new one. Careful not to change it.
I think the 993 is gapped large at .06 the old one might be at about .04 so could be that the coil can't fire that large gap. Just a theory.

 

[mkcustoms881]

Ok I will check that , if that's the case should I re gap the new plugs to what ever the old ones are?

 

[Schurkey]

Compare the '993s to the old plugs. Is the threaded portion longer? '993s have about a .900 reach, I bet the correct plugs have a .680 reach.

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

I don't recall a seven-cylinder engine being offered in a GMT400.

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Check with AC-Delco. Could be you're not supposed to re-gap the plugs. Problems with breaking-off the li'l Platinum [EDIT] Iridium [/EDIT] nubs, or bending the thin center electrode.

 

[wirlybird]

I have read that you should not try to re-gap them as it could damage them. However you could google it and especially for the Iridium ones.
The gap is a long shot theory!

 

[mkcustoms881]

I did say the engine 5.7

 

[mkcustoms881]

Ok thanks