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Need some help with my FAST

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  • Need some help with my FAST

    I am having an electrical issue after having a FAST ecm installed on my Sy. The speedo reads 30 mph when first started up and idling. I can turn on the lights and the speed goes to 20. I can then plug my power inverter into the cig lighter and the mph goes to 10. Then I can plug in my radar detector and the mph goes to zero. Has anyone that has installed a FAST in their SyTy had any electrical issues, or is this just a coincidence and I have other issues? I had my speedo checked and it is working fine.
    Cruzin' Mel Man
    Semper Fi

    Keep your fork

  • #2
    Are you saying that the Speedometer is reading 30/20/10 or are you saying that the Speedometer is reading correctly but the FAST is reading 30/20/10?
    Justin "RealFastV6"
    1991 GMC Syclone
    1993 GMC Typhoon

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    • #3
      I am saying the speedo is reading 30/20/10. I don't know how to check the speed readout in the FAST.
      Cruzin' Mel Man
      Semper Fi

      Keep your fork

      Comment


      • #4
        Your Speedo ground comes from a black cable that goes through the C100 connector that goes to the front drivers side intake bolt. It's shared with all the other things you mentioned.

        Location is C2 in the C100 Connector.

        I'd start with making sure that's there.

        Is this a Classic FAST or an XFI? Is it the adapter to the factory harness or a rip and replace of the factory harness?

        Justin "RealFastV6"
        1991 GMC Syclone
        1993 GMC Typhoon

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        • #5
          So RealFastV6, you are saying that it is just a coincidence that this happened when the FAST was installed and I have other issues? It is a FAST XFI 2.0. Also, it is the factory harness, re-pinned for the FAST. Do you have a FAST installed on your SyTy?
          Cruzin' Mel Man
          Semper Fi

          Keep your fork

          Comment


          • #6
            I wouldn't call it a coincidence - there was a significant amount of re-wiring that went on to install the FAST and there's a good chance that something got messed up or missed in that rewiring.

            The speedo only has three inputs.

            There's a Ground. (Let's check that first)
            There's a 5V reference.
            There's a Signal from the DRAC.

            Yes, XFI 2.0 in my Syclone.
            Justin "RealFastV6"
            1991 GMC Syclone
            1993 GMC Typhoon

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            • #7
              Thanks for the info, the ground will be checked.
              Cruzin' Mel Man
              Semper Fi

              Keep your fork

              Comment


              • #8
                Any update?
                Justin "RealFastV6"
                1991 GMC Syclone
                1993 GMC Typhoon

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                • #9
                  The Ground you are looking for is G109, originally it was located on front of the intake driver side.. However, if that ground isn't hooked up most things inside the cab want work.. for instance, Ashtray Lamp, Radio, Cig Lighter, Heater Lamp, Safety Belt Buzzer, Panel and Interior Lamp.. Etc..

                  Does your speedo working at all? Are you using the stock speed sensor from the transfer case or are you using an output from the Fast?
                  Syclone #0585

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                  • #10
                    It's a thought - but I can't see how the signal being messed up would show different MPH when the ground is impacted by different things being plugged into the cigarette lighter. I'm thinking more like poor ground circuit is gaining voltage +1V +2V, etc which is modifying the readout because the speedo references against it.

                    The FAST shouldn't be outputting to the Speedometer - it should be the DRAC directly to the speedometer.
                    Justin "RealFastV6"
                    1991 GMC Syclone
                    1993 GMC Typhoon

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                    • #11
                      I had the speedo tested and no problems were found, but not much else has been checked yet. I will probably know more after the new year. EVERYTHING was working fine before the FAST install and now the SPEEDO is reading erratically.
                      Cruzin' Mel Man
                      Semper Fi

                      Keep your fork

                      Comment


                      • #12
                        All wires, grounds and power, going to the FAST and gauge cluster have been checked, with no joy. What is the voltage suppose to be going to the DRAC? Does the FAST have an adjustment for speedo readings?
                        Cruzin' Mel Man
                        Semper Fi

                        Keep your fork

                        Comment


                        • #13
                          Finally got to do some more work on the Sy and I think the DRAC is bad. Does anyone have one, the broadcast code is AGS and the part # is 25073966.
                          Cruzin' Mel Man
                          Semper Fi

                          Keep your fork

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