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Is a Factory Tach compatible with an MSD Ignition Box...?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by JimmyUp, Apr 4, 2002.

  1. JimmyUp

    JimmyUp Registered Member

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    I believe I am getting incorrect rpm ratings from my factory tach. A couple of people have suggested that it could be due to the fact that the factory tach is not compatible with my MSD ignition box. My rpms seem to be registering higher than they should be. Anybody have any thoughts on this?

    Thanks!
     
  2. Greg72

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

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    What year is your Blazer?

    This thread just happened on the '69-'72 board. The simple answer is that even an MSD ignition will "mess up" a factory tach....the same way HEI does.

    There is a published schematic in that thread showing how to fix the problem by softening the "edge transistions" of the tach signal. No personal experience with it, but it's simple enough to build and try it.
     

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