[Daves1SS]

I changed my spark plugs back in May to the 1 step colder NGK LTR71X-11's,
(gapped at .039") and even though I'd notice some slight acceleration pulsing under VERY VERY light throttle (like barely pressing the gas) before the motor has fully warmed up, I didn't think much of it. Now that it has gotten much colder (30's in the morning), and especially when I have to park my car outside, the misfires feel much stronger in the same scenario. I have a Aeroforce Interceptor guage that reads misfires, and on cold operation it reads anywhere from 2 to 12 misfires on mega light throttle.

How you get 12 misfires from an 8 cylinder car, I don't know, but that's what the numbers read. Once the car warms up good you no longer feel the hesitation under super light throttle, but before it warms up good you feel them strong. It kinda bucks the car.

Once warm, and I get into the throttle, it pulls hard and never misses a beat, even at WOT to redline. However, I still once warm sometimes will show either 0, 2, or 4 misfires on the gauge. It mostly stays at zero, but not all the time. No KR to speak of (blips of 1 degree and less).

Any ideas? When I changed the plugs I also put on new GM plug wires and used plenty of the dielectric grease.

[SSDan]

Well, I'll play and state the obvious - why not put the stock plugs back in and see if you get the same misfire result?

In fairness - mine is completely stock and I have had a few rough idle/misfire cold starts - pretty rare though and certainly not at the level you are seeing.

[brettman]

I had the same problem, only when cold. It went from rough to missing to backfiring, in a short amount of time. Plugs were fouled (black)
Pull one of your plugs, see what it looks like.
However, I didn't throw a code, hard to believe the way it ran.

[motorhead]

Here's a good read that may help. Not insulting your intelligence. Just thought this might help.


https://www.ngksparkplugs.com/about-...rk-plug-basics

[Daves1SS]

I haven't changed back to stock plugs because I wanted to throw a post up here first, and it's challenging to find time to work on the car with my stupid busy life. I may just throw a fresh set of stock heat range plugs in it at an .040" gap ASAP and see if that changes it.
Are others with my setup running stock plugs still? Or is 1 heat range colder suggested?
I read up on it quite some time back and a lot of guys were throwing in these plugs I put in. But they may be too cold. My car gets driven every single day, often in heavy traffic which would mean not a lot of throttle and a lot of idling. They could just be too cold. No codes thrown here either.

[motorhead]

Originally Posted by Daves1SS

I haven't changed back to stock plugs because I wanted to throw a post up here first, and it's challenging to find time to work on the car with my stupid busy life. I may just throw a fresh set of stock heat range plugs in it at an .040" gap ASAP and see if that changes it.
Are others with my setup running stock plugs still? Or is 1 heat range colder suggested?
I read up on it quite some time back and a lot of guys were throwing in these plugs I put in. But they may be too cold. My car gets driven every single day, often in heavy traffic which would mean not a lot of throttle and a lot of idling. They could just be too cold. No codes thrown here either.

You're last statement would lead me to suggest going back to stock plugs.

[Daves1SS]

Originally Posted by motorhead

You're last statement would lead me to suggest going back to stock plugs.

Yea sounds like it, either stock or NGK 6509 LTR6IX-11.
Not sure the difference between stock and the 6509’s but have alerted Ted to this thread to get his input.

What is the stock plug again (type)? I am not sure I kept mine.

[brettman]

AC Delco 12622441

[Daves1SS]

Originally Posted by brettman

AC Delco 12622441

Perfect - thank you!

Ted replied to my PM and suggested I put in the NGK 6509 LTR6IX-11's.
I may try those first, and if that doesn't cure the problem throw in some stockers.

[motorhead]

Originally Posted by Daves1SS

Perfect - thank you!

Ted replied to my PM and suggested I put in the NGK 6509 LTR6IX-11's.
I may try those first, and if that doesn't cure the problem throw in some stockers.

He's the man. I would have no problem taking his advice. Good luck. Let us know how you make out.

[Daves1SS]

Originally Posted by motorhead

He's the man. I would have no problem taking his advice. Good luck. Let us know how you make out.

Will do, thanks man.

[toohighpsi]

I run the factory Z06 plugs in the boosted LT1s. Not sure if they're cooler (never checked heat range - they are gapped smaller), but they have worked well.

[Daves1SS]

I put the ones Ted suggested in, and left them at the gap they were already gapped at right out of the box (.041”) and they’re performing great. Kinda strange that my aero force interceptor still shows misfires (???) but maybe it’s some erroneous reporting because the car doesn’t ever stumble and feels great everywhere.

Here’s a pic of the worst of the 6510’s that I pulled out.
The others were very black, just not completely covered like this one was.

[brettman]

Man, that is really sooted up, very thick deposits. (like oil deposits)
Are the others thick? Mine were just a black film. I also gapped mine at .037, running approx 9 lbs boost. I hope that solves your issue. I won't if mine is OK till spring.