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Newbie needs input

This is a discussion on Newbie needs input within the Firebird / WS6 forums, part of the Vehicle Specific category; I recently bought a very clean 1998 TA, automatic and totally stock with 93K miles. It runs great! I did ...

  1. #1
    Junior Member
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    Red
    1998 Trans Am

    Newbie needs input

    I recently bought a very clean 1998 TA, automatic and totally stock with 93K miles. It runs great! I did replace the stock muffler with a flowmaster and put on 18" staggard wheels. Then I realized I was only getting 10 mpg. I took it to my mechanic and had him do a complete tune up, plugs, K&N filter, LOF, fuel filter and what ever else you would normally do. After all that money I am now getting 13mpg. I did research on here and saw others are getting much better than that. I also read about the 02 sencors so I took it back to him to check, he said there were no codes for that but I read they can be bad and still not show a code so I had the front ones replaced for another $300.00 charge and zero difference in mpg. Is there anything else I can do?
    Im 54 my driving habbits are calm and mostly all city. Is 13 mpg city the best I can expect? Thank you

  2. #2
    Big Gulps, huh? HOBS's Avatar
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    Black
    1999 Trans Am

    I get 17-18 in the city and with lets say spirited driving. The first thing that popped into my head was maybe your fuel pump is on its way out, so I'd have your mechanic check fuel pressure. Does your car seem to have plenty of power or does it still seem doggy after the tune-up?

  3. #3
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    Silver
    2000 Trans Am

    There has to be a problem. I get 17 with hard city driving. I average 20 in the city normally.

  4. #4
    Spaz is My Mentor SMWS6TA's Avatar
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    Navy Blue Metallic
    98 T/A w/a little mods...

    MAF needs seriously cleaned. Get a can of MAF cleaner and do it.


    K&N filters always effect the MAF because the oil from the filter gets on it and mess with it's readings.

  5. #5
    Moderator 35th-ANV-SS's Avatar
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    Red
    02 35th LE Camaro SS

    What Scott said.

    Any SES codes? How responsive is the car? Does it have good acceleration? Does it miss at all?

    Any black soot in the tailpipes?

  6. #6
    Veteran 0rion's Avatar
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    98 Formula
    06 duramax

    how are you calculating your mileage? Has your speedo been corrected for the tires and have you verified your speedo is actually accurate? Perhaps the prior owner had the rear replaced and a different ratio was installed.
    Last edited by 0rion; 07-18-2011 at 01:16 AM.

  7. #7
    Moderator 35th-ANV-SS's Avatar
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    02 35th LE Camaro SS

    One way to easily check your rear end ratio is to jack the rear of the car up. Make sure it's secure. Then, crawl under the car and mark the drive-shaft with a paint stick or something similar. Turn the wheel 1 full revolution and count the number of times the drive-shaft rotates.

    Ex: If you turn the wheel 1 revolution and the drive-shaft turns a little over 4X, you have a 4.10/4.11 ratio. If the drive-shaft turns 3-1/2 times, you have a 3.42 ratio. And so on...

  8. #8
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    Black & Blue
    '02 WS.6 / '07 Suburban

    Any actual signs of excessive fuel consumption such a black smoke coming out the exhaust or black spark plug electrodes?

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