Thread: Really Poor Gas Mileage

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  1. #1 Really Poor Gas Mileage 
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    so i have a 1999 Pontiac grand Prix GT 2 Door with the 3.8 V6 and i am getting super poor gas mileage... like less then 300 khm per tank of gas... and i am also getting a random misfire and cant figure out what it is???? my coil packs??? ignition module??? i cant find the random misfire... plugs and wires are less then a month old just replaced them

    Any advice would be greatly appreciated

    THANKS!
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  2. #2 Re: Really Poor Gas Mileage 
    GTX Level Member cerick08GP's Avatar
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    Well, one place to start would be the battery. Just recently a guy here had your exact same problem, after about a month of troubleshooting the problem was a bad battery draining down his system voltage.

    Other than that, had the codes scanned yet? Also, a coil would only affect two cylinders. But it could be the ICM.

    Ten years of continuous driving excitement and counting!
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  3. #3 Re: Really Poor Gas Mileage 
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    well im in the process of replacing the plugs wires and coils, and if thats not it i will do the ignition module i just know itll be a lot from the dealer...
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