I am new to this site but, I researched this site considerably before asking so please bear with me.

The car is a 2002 Firehawk, m6, 46000 miles and bone stock-it has all the SLP goodies. I recently changed the plugs and the store gave me the wrong plug, delco 41-993 with the gap set to .060. I wanted to use the standard delco plugs even tho this site suggests the NGK TR55. Once installed the car idled fine and ran as good as ever under light load. Under heavier loads, the engine seemed like it misfired. For instance, when the skip shift would engage and I shifted into 4th the engine would buck and sputter. At this point I would not see the SES light, however, if I continued to accelerate while the engine was bucking the SES light would flash until I left off the throttle.

I then installed delco 41-110 plugs and checked the gap at .040". Those plugs have been installed for 500 miles with no problems. Until now. Again, I am starting to get some bucking under heavier loads. My first thought is that perhaps the plug gap has changed from when they were installed but, I don't want to get target fixated.

Has anyone has a problem like this? What corrected the problem? Does anyone has any suggestions to troubleshooting this? Obviously, continuing to change plugs is not very fun or economical.

Thank you any input.

 

I'll try to point you in the right direction. .040 gap is ok although I like .055, just works better overall. Its possible you have a bad plug wire OR you cracked a plug when you installed them OR a wire has come loose. Sometimes you think you have the plug wires on but they are not on all the way. I always use a silicone lubricant on the inside of the spark plug boot so it snaps on easily.

I would carefully go over all the plug wires to see if any are loose. Also if you have a scanner you see which cylinders are miss firing, That can save time looking for the problem.

 

I would just use NGK TR-55 plugs from now on. They come pre gapped at .059 I believe and I've never had any problems with them.

 

I read on here that with iridium plugs, .060" was too much and caused the bucking problems, plus delco wrote a TSB that said the iridium plugs needed less gap. That's why I switched away from the delco 41-993. Now I'm confused.

I can go through and check the wires easy enough though. What electrode do the NGKs have, the TR55s?

Thanks for the help.

 

NGK TR55's gapped at .055

I had the same issue long ago and 2 of mine were cracked, and one fell apart when removed (the ceramic). Wasn't fuel related like I first thought.

 

My car hated the NGK's. I had a misfire with them at idle, and high rpms. I checked and re-checked for any problems with the plugs, but I couldn't find any.

I tried the Autolite 5245. First the copper, and now the double platinum, and my car loves them both. Runs smooth and feels good. I'll be sticking with the Autolites for now.