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Tach has power but not reading anything

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Dylastephens, May 13, 2019.

  1. Dylastephens

    Dylastephens Registered User

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    My tach is not working in my 1993 f350 7.3 idi with the e4od transmission causing it to go into limp mode. And sometimes the tach works and it shifts fine other times it doesn’t work at all and I have to shift it manually. I have pulled the sensor and cleaned it but nothing changed.
     
  2. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    How do the wires look coming out of the sensor?
     
  3. Slicknik

    Slicknik Registered User

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    @Dylastephens my guess is the sensor is toast that's in the block , check voltage at the sensor and contact points at the plug for burn marks

    Does it work over 1k + on the rpms and reads zero under 1k?
    Does is shift fine at 1/2 to full throttle ?
    Does the trans hunt in stop go city driving?

    There are also two more senors , ones in the trans and the other is in the diff
     
  4. Chrono558

    Chrono558 Registered User

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    When the tach is dead, is the O/D light flashing or is it off as well? If the tach is dead and the O/D light is off (not flashing) then I'd suspect that the TECA is losing power or ground somewhere.
     
  5. Dylastephens

    Dylastephens Registered User

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    The tach Either works fine or not at all and my od light never comes on even when I press the button the light won’t come on and my speedometer works so I don’t think it’s the speed sensor and when I put it in drive it is in a high gear at all times unless the tach works
     
  6. Dylastephens

    Dylastephens Registered User

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    Where is the teca and what sensor is in the trans and rear end
     
  7. SOCAL_Redneck

    SOCAL_Redneck Registered User

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    Literally just dealt with the same thing in my truck, take Slicknik advice and check out the sensor. I got one from partsgeek.com for $40 plus shipping and it got rid of the hunting issue and tac not responding.
     
  8. Slicknik

    Slicknik Registered User

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    @Dylastephens , your case is a little different, you don't have a light on at the OD switch or flashing for that matter, so you need to check the ground for the switch and find out if your getting power or not ,
     
    Last edited: May 15, 2019
  9. Dylastephens

    Dylastephens Registered User

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    I found out that the tach only works if the engine is warmed up and once it is warm I can shut the engine off and restart it and it works fine till it cools down
     
  10. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Sounds like a bad sensor. Still haven’t answered my q about the wires coming out of the sensor. Those tend to become bare over time
     
  11. Dylastephens

    Dylastephens Registered User

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    The wires are fine
     

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