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Tach Problems

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigJohnson, Sep 15, 2001.

  1. BigJohnson

    BigJohnson 1/2 ton status

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    I've got an Autogage tach that I can't get to work properly. I hooked it up following the directions. Green to tach terminal on my HEI, black grounded to the battery, white to switched 12v for back light, and the instructions say the last wire is an optional 12v source. When I hook up all the wires but the optional one the tach does nothing, it stays around 500RPM. When I hook up the optional 12v wire the tach goes down to about 200RPM and never gets above 1000RPM when driving around. I have wired everything with good connections and grounded it directly to the battery. Also, it is set to 8 cly. inside. What could the problem be?
    Thanks,
    Jordan
     
  2. dragricinMT

    dragricinMT 1/2 ton status

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    Where exactly did you ground the wire to? Also the wire you say is optional is your power wire. All 4 wires need to be hooked up. Red wire needs to be hooked to a constant 12volt source with key on. Make sure green wire is connected securely to tach terminal{not loose to move around when driving}.
     
  3. BigJohnson

    BigJohnson 1/2 ton status

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    I grounded it directly to the negative terminal on the battery. Its got a good connection at the distributor. Should I move the ground somewhere else?
    Thanks,
    Jordan
     
  4. dragricinMT

    dragricinMT 1/2 ton status

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    Yes. Ground it to the metal dash. I have an autogage and a 5" autometer and both are grounded to dash. The ground needs to be to the body.

    Let me know if this works. JR
     
  5. Liberator

    Liberator 1/2 ton status

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    This may be a dumb question, but did you set it for an 8 cylinder?

    Bo

    If it breaks, it wasn't good enough!
     
  6. BigJohnson

    BigJohnson 1/2 ton status

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    I moved the ground to the dash and nothing. Just like before. Then I decided to move the switch inside to the 4 cly. position. Now the tach seems to work. It idles around 500RPM and when I shifted the tranny manually I was able to rev it to 4000RPM. I still don't know if it is right or not. I guess 4000RPM is a good bit for a stock 350, it sounded like about all it would take.
    Thanks for the help,
    Jordan
     
  7. Thunder

    Thunder 3/4 ton status

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    Sounds like its hooked up correctly. The cyl selection switch works in one position but not the other? It looks like you got a bad tach. I would take it back and get a new one.

    <a target="_blank" href=http://coloradok5.com/gallery/Thunders-Blaze>http://coloradok5.com/gallery/Thunders-Blaze</a>
    <font color=blue>NEVADA: Where the pavement ends, and the West begins.</font color=blue>
     
  8. TorkDSR

    TorkDSR 1/2 ton status

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    what rpm does the tack say at 60 mph in full lockup with what rears and tire size?

    Tork DSR
    I just got a winch, it takes the fun out of things.
     
  9. BigJohnson

    BigJohnson 1/2 ton status

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    Its around 1800 to 1900RPM with a TH400, 3.08 rear gears, and 31inch tires. That sounds close, right?
    Jordan
     
  10. TorkDSR

    TorkDSR 1/2 ton status

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    right on the way i figure

    Tork DSR
    I just got a winch, it takes the fun out of things.
     
  11. chevyracing

    chevyracing 1/2 ton status

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    Sounds like you may have figured it out but one more thing to check is to make sure it is for an HEI and not a points system. There is a thing-a-ma-bob I had to put on my cheap little sun tach to use it on HEI.

    John

    Like to go sloppin' 'round in da mud in a rapid fashion....=)
     

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