Sunpro tach bouncing

Electrical & Ignition

  1. wagonman

    wagonman Well-Known Member

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    just got done with the HEI conversion. Went from a GM 990 module and an older oil filled coil to a Pertronics 60103 coil and Accel 35361 module. Now the tach bounces what am I missing? IMG_0552.JPG
     
  2. 64SF

    64SF FBBO Gold Member FBBO Gold Member

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    I’ll be watching have a similar problem. Bounces and reads high.
     
  3. wagonman

    wagonman Well-Known Member

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    Same Sunpro Super Tach 2 ??
     
  4. Bee1971

    Bee1971 Well-Known Member

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    The HEI module is still an inductive discharge ignition system

    You just installed a very low ohm primary resistance E coil designed around the Pertronix Ignitor 111 module

    Try installing your canister type oil filled coil and see if your Tachometer reads correctly , and then
     
  5. wagonman

    wagonman Well-Known Member

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    Looking at My own Pic and you can see where the yellow tach wire is on the Coil tower and boot. Moved it and still the same.
     
  6. wagonman

    wagonman Well-Known Member

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    Will have to source another coil as the old one is junk.
     
  7. Bee1971

    Bee1971 Well-Known Member

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    Any old 1.4 - 1.5 OHM primary resistance oil filled coil

    Your just doing a simple test first , then
     
  8. Gsmopar

    Gsmopar Well-Known Member

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    Define “bouncing.” I’ve had a bad plug wire cause the tach to bounce.
     
  9. kiwigtx

    kiwigtx Trendsetter Staff Member FBBO Gold Member

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    Needle fluctuating incorrectly according to RPM of engine is how I read that.

    You may be experiencing "High voltage induction" due to the tachometer supply wire being too close and /or running almost parallel to the HT lead off the centre of the coil.

    This is a condition which can be cured (or disproved) by simply running the wires away from the HT cable, and as a test you could wrap the wire in foil. Normally I would run a twisted pair with a foil screen to really be sure of getting rid of that problem. I have done this before on a bespoke ignition system in a Hot-rod.
    Same problems can arise when running a Hall-effect speedometer and too close to ignition cabling.
     
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    • wagonman

      wagonman Well-Known Member

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      It has newer plug wires on and the engine runs fine, I will give the foil a try and also the twisted wires also wrapped.
       
    • Don Frelier

      Don Frelier FBBO Gold Member FBBO Gold Member

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      • Don Frelier

        Don Frelier FBBO Gold Member FBBO Gold Member

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        But seriously if you install a shielded cable with a drain wire.
        Cut and heat shrink at the coil end and then strip out and ground near the tachometer.
         
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        • Agree Agree x 1
        • wagonman

          wagonman Well-Known Member

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          Thanks Don, after doing some research I did what you suggested with some foil and a drain wire wrapped in electrical tape and heat shrink. It worked thanks again.
           
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          • Don Frelier

            Don Frelier FBBO Gold Member FBBO Gold Member

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            I have a bunch of 9463 let me know if you would like some.
            Screenshot_20210619-143215.png
             
          • wagonman

            wagonman Well-Known Member

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            Sure I will take what ever you think is best. PM Coming.
             
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