working on my friends z28 today, again. 95 z28, motor is an lt1, lt4 heads, lt4 intake, 383, 230/236 cam, ltcc, and a dyno tune, wot 12.5:1 afr, no knock.

for some reason, the car is eating spark plugs. they fail after as little as 20 miles. when one or more fails, the car has a noticeable stumble and chugs really bad.

replacing the plugs *always* resolves the problem for a short period of time. taking ohm readings of the plugs finds 1 or more with very inconsistent readings from the others.

any thoughts on what this could be? we have tried ngk, autolite, ac delco plugs, all with the same results. we are really bored of doing plug changes on this thing.

should we try a colder heat range? could it be under hood heat? totally lost.

thanks for the help.

 

What is the failure mode of the plugs (missing electrode, fouled)?

 

neither. they look perfect when pulled out. but if you resistance test them, they are all over the place and usually over 10kohms.

 

Is that checking wire end to center electrode, or to ground? Any signs of arc tracks along the outside of the ceramic, from the boot to the metal body?

 

its checking from the center electrode to the stud where the wire connects.

no signs of arc tracks, no cracks in the ceramic, nothing.

 

Hmm. I frankly don't know what plug resistance should be, as I always test them by making them spark, and looking. Even searched for a spec.

 

I've seen some plugs do this if they are overtightend. Also take the rubber out of the spark plug socket if using one or just use a regular socket. The rubber can cause side loading of the porcelin. Can't think of any engine issues that would cause resistance failure so soon.

 

Also make sure your not cracking the plugs when you install them, this can make them arc to the engine and cause a miss. Dropping them can cause this also.

 

of course a few have been cracked at install, but i always pull them out and replace them. if i drop one, it gets junked as well.

tks for the infos.