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Tachometer recalibration information

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  • Tachometer recalibration information

    I saw this on facebook and thought it was important to post here

    ‎Jose A Berrios‎ to SyTy.net

    I noticed my tach was reading 1000 rpm at idle but my scanner was reading 750 rpm..at 4000 rpms at the dash tach the engine was really at 3000..i read that gm tachs go out of calibration because of a calibration resistor chip drifting ..i opened mine and i found the same calibration chip...to make the story short look at the pictures...i just removed the solder from the pins 4 and 10 on the white chip to remove it from the circuit..this is the bad resistor that drifted out of calibration...and in the same board there is a place marked r 14..there you just install a trio of resistors in series..2 100k and one 47k...total resistance will be 247k ohms...my original measurement of the chip was 306k...i hope this write up can help some of you





    Aaron T.
    Syclone #1084 AKA Crispy
    http://i151.photobucket.com/albums/s...psa99a8e26.gif

  • #2
    Re: Tachometer recalibration information

    the 4 cylinder board looks totally different. I will try to pull one out of the shed in the next few days...
    Aaron T.
    Syclone #1084 AKA Crispy
    http://i151.photobucket.com/albums/s...psa99a8e26.gif

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    • #3
      Re: Tachometer recalibration information

      I know this was also a problem for the G body cars. Specifically the Pontiacs. My mothers grand Prix had to go in to be recalibrated twice. My 2+2 was also way off but I never ended up fixing it. Maybe looking at the G body v8 tach will yield the correct resistor value to calibrate a syty for a v8 readout.

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      • #4
        Re: Tachometer recalibration information

        Good thinking to post it here.
        Not sure how easy it would be to find a post like this on Facebook if you are looking for the information sometime in the future.
        1991 Syclone 2241 - 87k miles
        2006 Cobalt SS
        2006 Trailblazer SS AWD
        RIP 6/10/08 1998 Saturn SL2 #1 - 236,456 miles
        RIP 12/12/13 1998 Saturn SL2 #2 - 315,000 miles

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        • #5
          Originally posted by Static View Post
          Re: Tachometer recalibration information

          Maybe looking at the G body v8 tach will yield the correct resistor value to calibrate a syty for a v8 readout.
          Did you ever find out?
          Kenneth R Zink II
          2001 Chevy S10 - Turbo 4.3L SFI conversion (Black Beauty)
          2000 GMC Jimmy SLT - Stock (J10)
          1994 Olds Bravada - Soon to be 455 Olds powered (Rocket)

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          • #6
            Negative.

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            • #7
              Originally posted by hellcat1 View Post

              Did you ever find out?
              Use 100k+50k resistors and a 100k potentiometer to find out exactly, but I suspect it's 200k.

              Unless you're talking about an LS1 - in which case it seems most people just change the LS1 ecu output to output for a V6 tach instead.


              Last edited by RealFastV6; 12-27-2017, 11:14 PM.
              Justin "RealFastV6"
              1991 GMC Syclone
              1993 GMC Typhoon

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