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89 IROC Tach Repair

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  • 89 IROC Tach Repair

    Just picked up an 89 IROC vert, the tach reads about 800 rpm high, and when you wind the car out it floats ahead well into the red zone, past 6500 rpm, when the car is really at about 4500 rpm. GM doesn't sell the gauge cluster anymore, anybody know of where to get these things fixed?

    Greg

  • #2
    YearOne sells a LOT of restore parts.
    -Ryan-


    1997 Pontiac Firerbird Formula LT1/T56
    2006 Pontiac G6 GTP, 3.9L V6, 6-spd

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    • #3
      It is possible the tach failed and somebody replaced it with a used one from a V6 car. That would exactly replicate what you say is happenning.

      I had the tach fail in my 88 Iroc and ended up just replacing the circuit board on the back of it. I re-used the gauge itself. Just make sure you get a board from a V8 car. It's fairly simple to replace once the cluster is removed from the dash.
      Tracy
      2002 C5 M6 Convertible
      1994 Z28 M6 Convertible
      Current Mods:
      SLP Ultra-Z functional ramair, SS Spoiler, STB, SFCs, Headers, Clutch, Bilstein Shocks, and TB Airfoil. 17x9 SS rims with Goodyear tires, 160F T-Stat, MSD Blaster Coil, Taylor wires, Hurst billet shifter, Borla catback with QTP e-cutout, Tuned PCM, 1LE Swaybars, 1LE driveshaft, ES bushings, White gauges, C5 front brakes, !CAGS, Bose/Soundstream audio, CST leather interior, synthetic fluids

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      • #4
        Originally posted by TraceZ
        It is possible the tach failed and somebody replaced it with a used one from a V6 car. That would exactly replicate what you say is happenning.

        I had the tach fail in my 88 Iroc and ended up just replacing the circuit board on the back of it. I re-used the gauge itself. Just make sure you get a board from a V8 car. It's fairly simple to replace once the cluster is removed from the dash.
        Thanks, I'll head down to the dealer and get a circuit board. Why didn't I think of that. Thanks for the help.

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        • #5
          you can get used gauge clusters for around 50 bucks. try the classifieds on thirdgen.org
          87 GTA: it's winter time, all tore apart

          ConElite: "Im 22, have had my TA since I was 21."

          "I wont lie, I have a heavy foot, but at the same time I know when its the safest to ring out a gear or 2."

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          • #6
            Originally posted by gage
            Thanks, I'll head down to the dealer and get a circuit board. Why didn't I think of that. Thanks for the help.
            I don't know if the dealer sells that seperately. I got mine from the local pick-a-part. I just walked around the salvage yeard until I found a V8 3rd gen. It was a totalled 82. It was t-boned and the dash was all busted up. I gently (LOL) removed the gauge cluster and the circuit board for the tach was untouched. I took the circuit board up to the front desk and they didn't even charge me for it because they agreed it was junk and might not even work. Well, it did work perfectly!
            Tracy
            2002 C5 M6 Convertible
            1994 Z28 M6 Convertible
            Current Mods:
            SLP Ultra-Z functional ramair, SS Spoiler, STB, SFCs, Headers, Clutch, Bilstein Shocks, and TB Airfoil. 17x9 SS rims with Goodyear tires, 160F T-Stat, MSD Blaster Coil, Taylor wires, Hurst billet shifter, Borla catback with QTP e-cutout, Tuned PCM, 1LE Swaybars, 1LE driveshaft, ES bushings, White gauges, C5 front brakes, !CAGS, Bose/Soundstream audio, CST leather interior, synthetic fluids

            Comment


            • #7
              Originally posted by MunsonGTA
              you can get used gauge clusters for around 50 bucks. try the classifieds on thirdgen.org
              But then you face the issue that different models and years had different gauges. The speedometers were different, the redline on the tach was different, etc.

              replacing just the circuit board allows you to keep the same gauges. Plus, the circuit boards are easy to find in a junkyard very cheap. All years were the same until they updated the interior in the 90s., it just has to be a V8.

              Just try not to destroy a good gauge cluster at the junkyard to get the circuit board. Look for one that is already messed up and leave the good ones for guys that need the entire cluster.
              Tracy
              2002 C5 M6 Convertible
              1994 Z28 M6 Convertible
              Current Mods:
              SLP Ultra-Z functional ramair, SS Spoiler, STB, SFCs, Headers, Clutch, Bilstein Shocks, and TB Airfoil. 17x9 SS rims with Goodyear tires, 160F T-Stat, MSD Blaster Coil, Taylor wires, Hurst billet shifter, Borla catback with QTP e-cutout, Tuned PCM, 1LE Swaybars, 1LE driveshaft, ES bushings, White gauges, C5 front brakes, !CAGS, Bose/Soundstream audio, CST leather interior, synthetic fluids

              Comment


              • #8
                Just bought a used gauge cluster on ebay and got it today. So is the circuit board the yellow box with the wires that plug in over by the back of the speedo? thanks

                Comment


                • #9
                  Originally posted by TraceZ
                  But then you face the issue that different models and years had different gauges. The speedometers were different, the redline on the tach was different, etc.
                  they have every different kind of cluster you could possibly want on tgo.

                  145 Speedo - $60 + shipping
                  $60 + shipping. Came out of 89 IROC. USPS M.O. only

                  (may be worth $100 but just can't do it)

                  Located in Spring, TX.

                  this guy ended up GIVING it to another tgo member and even paid shipping.

                  http://www.thirdgen.org/techboard/in...0-shipped.html
                  87 GTA: it's winter time, all tore apart

                  ConElite: "Im 22, have had my TA since I was 21."

                  "I wont lie, I have a heavy foot, but at the same time I know when its the safest to ring out a gear or 2."

                  Comment


                  • #10
                    Originally posted by gage
                    Just bought a used gauge cluster on ebay and got it today. So is the circuit board the yellow box with the wires that plug in over by the back of the speedo? thanks
                    If you take the cluster completely apart and remove the tach from it, on the back of the tach you will see the curcuit board. A few nuts and it will come free of the gauge.

                    The gauges are held into the cluster with pressure pins. Once the bezel and clear lense are removed the gauges just pull out.
                    Tracy
                    2002 C5 M6 Convertible
                    1994 Z28 M6 Convertible
                    Current Mods:
                    SLP Ultra-Z functional ramair, SS Spoiler, STB, SFCs, Headers, Clutch, Bilstein Shocks, and TB Airfoil. 17x9 SS rims with Goodyear tires, 160F T-Stat, MSD Blaster Coil, Taylor wires, Hurst billet shifter, Borla catback with QTP e-cutout, Tuned PCM, 1LE Swaybars, 1LE driveshaft, ES bushings, White gauges, C5 front brakes, !CAGS, Bose/Soundstream audio, CST leather interior, synthetic fluids

                    Comment


                    • #11
                      Originally posted by TraceZ
                      If you take the cluster completely apart and remove the tach from it, on the back of the tach you will see the curcuit board. A few nuts and it will come free of the gauge.

                      The gauges are held into the cluster with pressure pins. Once the bezel and clear lense are removed the gauges just pull out.

                      Glad I asked...I would have installed it back in the car with the new yellow box thinking it was the circuit board. Thanks

                      Comment


                      • #12
                        Swapped the circuit board from the used tach. When I start the car the rpms jump to 3k so now it reads 2000rpm too high... Is the circuit board bad from this car too or is something else amiss?

                        Comment


                        • #13
                          Originally posted by gage
                          Swapped the circuit board from the used tach. When I start the car the rpms jump to 3k so now it reads 2000rpm too high... Is the circuit board bad from this car too or is something else amiss?
                          That's odd. Do you have an aftermarket tachometer laying around that you could use to verify the signal going to the tach is good?

                          Do you have the gauge the new board was originally on? Maybe try swapping the gauge as well just to see if that narrows it down.
                          Tracy
                          2002 C5 M6 Convertible
                          1994 Z28 M6 Convertible
                          Current Mods:
                          SLP Ultra-Z functional ramair, SS Spoiler, STB, SFCs, Headers, Clutch, Bilstein Shocks, and TB Airfoil. 17x9 SS rims with Goodyear tires, 160F T-Stat, MSD Blaster Coil, Taylor wires, Hurst billet shifter, Borla catback with QTP e-cutout, Tuned PCM, 1LE Swaybars, 1LE driveshaft, ES bushings, White gauges, C5 front brakes, !CAGS, Bose/Soundstream audio, CST leather interior, synthetic fluids

                          Comment


                          • #14
                            Originally posted by TraceZ
                            That's odd. Do you have an aftermarket tachometer laying around that you could use to verify the signal going to the tach is good?

                            Do you have the gauge the new board was originally on? Maybe try swapping the gauge as well just to see if that narrows it down.

                            Yes, I put the donor gauge on there too and it behaves the same way....at idle the tach shows 3k, then revs from there...I put the orig tach and its board (the one you think is a v6 board) back in, idle at 1500, then same symptoms,revving way higher than the engine. I did notice that the board from my car and one from the donor gauge are different, diff part #s, circuit transistors are different size, so you may be right, it might be from a v6. I guess I got a bad donor board on ebay. Hopefully the guy will give me my $50 back. This is driving me crazy. Frustrating that no one makes these circuit boards. They make circuit boards for 75 vettes, but not for lates 80s camaros...I guess until the 3rd gens are considered antiques, no one is going to repro parts. Until then we stuck with used parts and cross your fingers...

                            Comment


                            • #15
                              ok, bought another ebay tach...it behaves the same way as the orig tach, reading about 13-1400 (waytoo high )at idle, then it revs way too high also. I disconn white wire at coil and hooked it to my shop tach...idle is 700-800 rpm, just right. I also hooked the tachs from the car straight to the coil wire, same behavior (elimnates the circuit board on the cluster) I notice the circuit board on the tach I just bought is the same physically as the one on my orig tach, which both differ from the 2nd tach I bought, which read 3000rpm at idle....This is driving me nuts. I guess I got another tach with a V6 circuit board. The shop tach reads correct so these other tachs must be messed up.

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