Thread: Misfiring after 100mph!

Okay guys i have a 2004 grand prix gtp competition package and it has 102k miles. Got the car checked out by a shop because of a random misfire after like 100mph or more. Only on freeway in the streets its fine no codes thrown or anything. Mechanic said start with a transmission fluid replacement and see from there and still charged me not answering why it was misfiring. He said everything looked good. What should i do. I changed the fluid in the transmission 2 weeks ago at another shop. Car runs great until 100 and more! Please help I'm tired of paying mechanics for no answers!
I was thinking of taking it to gm


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Plugs fuel filter etc done. Tune up done! I cant think of anything else.


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Yes its on and off. Yesterday was driving down the freeway. One pull i did full throttle and around 100ish it started flashing. So i let go off the gas because i don't want to damage anything. So i wanted to see it again to try to figure out if it happening constinetely and i did a pull to 110mph and no flashing. So it really weird


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What kind of plugs did you install? Also, did you reuse the old wires? The flashing is showing a possible catalyst damaging misfire as you seem to know.

Thats doesn't sound good! I already have changed the catalytic converter i got warranty but still would suck to pay labor again. New bosh wires with ngk i believe.


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Its been about 10k miles since i did the wires and plugs. I did the catalytic converter also with 02 sensor. Why would it happen only at high speed possibly overdrive


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Does it happen while cruising or WOT? By the sound of it, you're WOT 3rd gear...lots of load...probably around 4000RPM...

Correct! It only happens at wot high speeds! But not at low speeds. I can full throttle from a dig and go and no problem


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It's the load...possibly MAP/MAF related. I'd love to see freeze frame data on it.

I know i don't but i want to fix the problem or just fix it. Im just trying to conclude wether i should get rid of it or not. Cus if its serious i don't want to deal with it. But yes i understand but these cars are pretty strong they shouldn't have a problem at 100mph. I wish it was running 100 percent


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Thanks whats freeze frame data? I may get a second opinion by a gm mechanic here in my city hes very familiar with gm cars


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Yeah i already put in like 2k of mechanic work in the last year and a half!!!


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Cool. Ill have to look into that! Definitely sounds like kr


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I wont be doing pulls until i find out exactly issue and fix it. Ill see thanks for the information tho


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