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Thread: why can't I get my speedometer accurate?

  1. #1
    Junior Member
    Join Date
    May 2012
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    43

    Default why can't I get my speedometer accurate?

    I've been battling this thing for weeks.

    Adjusting revs per mile in the TCM, pulses in the ECM.

    No matter what I'm out 15% to the low.

    It's a 3.73 gear truck with 325/60R20 Nitto Terra Grapplers

  2. #2
    Lifetime Member tokymon's Avatar
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    Apr 2008
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    i just adjust in the ecm and messure the tires and put that in not what the tire calc says. (ie. tires= 35x12.5x16 but messure only 34.5 tall)
    97 2500 ecsb 5.7l/4l80e/4x4 411 pcm /thorley tri-y's/dual super 40's with x (catless)/aem cai/msd 6a and coil/zz4 cam/beehive spring/lm-1

    stock sucks

  3. #3
    Lifetime Member
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    Jul 2012
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    Post up the tune and ill look at it later tonight
    14 GMC Sierra
    5.3L CC SB 4x4
    Basic tuning....

  4. #4
    Lifetime Member minytrker's Avatar
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    Jan 2006
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    1,332

    Default

    Quote Originally Posted by tokymon View Post
    i just adjust in the ecm and messure the tires and put that in not what the tire calc says. (ie. tires= 35x12.5x16 but messure only 34.5 tall)
    THats the trick, almost every all terrain or mud tire I have measured was always off. All the low profile 22's, 24's, etc are usually dead on though.

  5. #5
    Lifetime Member THEFERMANATOR's Avatar
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    Mar 2009
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    DON'T CHANGE THE TCM, LEAVE IT ALONE! All you are doing by changing the TCM is changing your shift points and throwing your adapts off. The factory calibration is set up and should work pretty well with most combos regarding of gearing. Only make changes to the ECM for speedo changes. If you know your actual speed VS displayed speed, go into the speedo calculator select speedo fine tuning, and put in the numbers. This will get it pretty dang close.
    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.

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