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Stock tach with HEI

Discussion in 'The Garage' started by TONYP, Sep 16, 2002.

  1. TONYP

    TONYP 1/2 ton status

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    my tach reads way to high with the HEI. will it work with it or do I need a new one? I have one wire running to the tach from the HEI, and the other wire runs to the + batt., anyone seen this or is my tach a goner /forums/images/icons/crazy.gif
     
  2. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    THe GM tach harness has a resistor inline on the wire from the tach to the dist, do you have this? I've also had my tach become very erratic with charging system problems.
     
  3. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Tony,

    You need to build this:

    [​IMG]

    This is the schematic to cure the high tach readings with HEI and a stock tach.

    Enjoy! /forums/images/icons/cool.gif
     
  4. kennyw

    kennyw N9PHW Premium Member

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    Is this for a vehicle that orignally used points? Because my 79 K10 Doesnt use this setup. It just has 3 wires: power, ground and direct hook up to the HEI tach slot.
     
  5. Michael

    Michael 1/2 ton status

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    The schematic is just a (factory) filter that appears to have been starterd in '81 or so. Earlier models didn't seem to have them. I believe Tony has a '72 that used a different style factory tach that was used with points.
     
  6. TONYP

    TONYP 1/2 ton status

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    it is a 72, so it did work with points. Going to make one up and see if that does the trick.
     
  7. TONYP

    TONYP 1/2 ton status

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    Greg,
    Have a guestion on the "15 MF", the guy that put it together put in a "15 MFD" But hes not sure what the 15 MF is. Wnats to know if it's a passive or ceramic relay. Not sure if I'm tell you the right things or not so if you need more info let me know.
    Thanks
     
  8. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Tony,

    Those parts are capacitors....usually rated in Farads. The smaller values will be in Microfarads (MF or MFD are both acceptable abbreviations), or the REALLY small ones are PicoFarads (PF, PFD, or sometimes called "puffs" by the E.E. Guys! /forums/images/icons/grin.gif )

    Neither are relays....I think he may be asking for the type of capacitor you want....ceramic is one style, there are other types also. I don't know enough about the materials to know which is BEST....it may just come down to the power rating it's designed for, and the accuracy (1%, 5%, 10%)????

    I know for resistors, those are some of the considerations....with "caps" I suppose it's the same deal.

    Sorry I can't help more....I'm not an Electrical Engineer. I just saved that image the last time this post was answered, since I figured someone else would need it! /forums/images/icons/cool.gif

    I chickened out and bought an MSD ignition and Autometer tach so solve my accuracy problems........ /forums/images/icons/tongue.gif
     
  9. Michael

    Michael 1/2 ton status

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    Just stick in whatever 15 micro farad you can get...this is just a filter...no need for tricky parts.
     

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