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Tach Bouncing??

Discussion in 'The Garage' started by MTBLAZER89, Oct 3, 2003.

  1. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    My tach bounces about 200-400 RPM's until I hit 3000 RPM's then it is smooth until it shifts. I can't "feel" anything wierd while it is doing it. The coil and pickup both checked good. No codes. Also it idles about 500 RPM's when it is warm /forums/images/graemlins/confused.gif

    1989 350 TBI.....Any ideas?
     
  2. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    My OE tach acts really wierd when the alternator is failing.
    /forums/images/graemlins/thinking.gif
     
  3. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    My OE tach acts really wierd when the alternator is failing.
    /forums/images/graemlins/thinking.gif

    [/ QUOTE ] You guys have factory tachs? NO FAIR! /forums/images/graemlins/grin.gif /forums/images/graemlins/frown.gif
     
  4. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    Nope mine is a Sun Meter........Any Ideas
     
  5. bigblock454

    bigblock454 Clack Clack Clack Premium Member

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    Mine does it also, not sure what brand but I haven't been able to fix it on my 88 V3500 454
     
  6. bablazer73

    bablazer73 1/2 ton status

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    by chance, do you have access to an inductive digital tach? check and see if it's actually accurate? I know some of the "less expensive" tachs are prone to this, But i had a problem with a autometer tach that did that. I had to use a signal wire with a stainless sheild over it. The signal going in was affected by the "rf" put out by my ignition system. It was not noticeable at higher rpm's because the pulse signal was faster.
     

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