I have a problem with my SS/NA Auto. I'll be cruising at highway speeds and when I floor it, it will occasionally "misfire" between 5-6.5K RPM. No codes are thrown, and its very brief. It doesn't happen too often, and my buddy with a 1998 Grand Prix had the same problem. The only mod I have is an intake, and I only have 103,xxx miles. Any help? Thanks guys

 

Whats your maintenance like?

 

Pretty good. Just had all my fluids changed and my transmission looked at when I passed 100K miles. Always on top of my oil changes and I use synthetic. I used to be rough with the car, but now I baby it and only floor it when I really need to. And a vast majority of my miles are highway.

 

Spark plugs?

 

They were changed at probably 70,000 miles. I can check tomorrow, but they shouldn't be bad after 30,000 miles...or could they?

 

Iridiums shouldnt be. Pull them and check color

 

Most likely the coil using a scanner take the car out and scope the coils and look at the firing pattern one should look different and thats how you will know which coil is faulty. If your scanner doesnt scope then either do a powerflow test while driving or view the misfire monitor. If its misfiring it will be stored under history codes but doesnt occur enough to set the light

 

Did you pull the plugs? They can tell you a lot, and you can check the gap. Besides plugs it's probably the coils as mentioned

 

i had a misfire problem before and it was my cat, the core had turned inside so when i put the hammer down it would start misfiring around 6000rpm so i took the down pipe out and punched it for now and has run fine ever since.

 

I had misfire as well with stock cat

my 2 cents

 

I had this problem, although my misfire was at 4,000 rpm, and the CEL code I pulled was for cylinder 1. I first changed all 4 of my spark plugs, and still had the problem, so I simply swapped out a new ignition coil. No problems since!