engine misfiring

i have had an ongoing problem with my engine misfiring. it is a 99 gtp. the odd thing is that only one side of the engine misfires. basically, under heavy throttle, the spark plugs crack on that same side. i have replaced them over and over, and have been to numerous mechanics; even a dealership, with no luck. if anybody could have an idea as to why this would happen, please let me know.

What plugs are u running?? Stock??

That is exactly the same problem I have and guess what it is the exahust manifolds. What happens is that with time these manifolds develop thin and long cracks that get thicker with time. I bet that after you replace the plugs the car runs fine for a couple of days before the missing starts again. If that is the case the heat escaping the exahust manifold is heating to much your plugs and thus cracking them. In my case there are instances where even the cable gets all burned out. I will install headers but you can get ported exaust manifolds and that will heal the problem. I bet your problem plug is either 3 or 4

Well, I have had a few different plugs (have been through many because of this) but I tend to use AC Delco. They are the stock heat range, but that should be adequate. I have only installed an exhaust and CAI, so that shouldn't be a problem either.

Sounds like it could be the manifolds, your (kilroypr) description was pretty much on point.

If anyone has any other ideas, they would be much appreciated. Thanks for the feedback. I'll be checking the manifolds.

try some Autolite 605's or 104's
605 = stock heat range
104= 1 - 2 heat ranges colder


They are bout a buck a plug and ive never seen them crack. I have seen many AC Delcos crack and would never run them in my car.

To tell you the truth I think Ripn12s is into something with the sparks. I have installed Champions 408cp(Aka. they are the champion version of the Autolites 104)and the cables have got burned but the plugs are pretty much ok. I feel the car is behaving better because they are making the car run cooler along with the cooler tstat. And for the record what the car had installed where the NGK's not AC Delco. I feel the cracking is more related to the heat range not the brand.

if it were the plugs, though, wouldn't all of them crack, and not just the front three? i have had no problems with the back three plugs.

Id say try the autolites and see what happens. I mean you'll only be out 6 bucks.

ok, thanks. i'll see what happens.