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Thread: Tachometer way off

  1. #1
    Senior Member
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    Default Tachometer way off

    So the tach in my 1988 Ciera 3.8L FE3 coupe is off by a factor of at least 2 or 3. At idle it's at least 2K and when I just mildly hit the gas it jumps to around 5K and if I actually step on it, it buries beyond the 7k RPM max. I can hear that the RPMs are clearly not that high, plus I haven't blown my engine yet.
    Any ideas what's going on here?
    Does the computer use this data for anything that would affect drive-ability? It's been this way for a while and I've not noticed anything, plus it's my beater car, so I'm not overly concerned. Just curious.

    Thanks

    Dan



  2. #2
    Senior Member Keiths1976's Avatar
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    There is a ohm resistor in the tach that is that is going bad . The gm cars use the pulse from the ignition control modular and breaks it down and transfer that to actual rpm reading .

  3. #3
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    Thanks for the info.

  4. #4
    Junior Member adambweird's Avatar
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    Ive had a very similar problem on my 87 for quite some time, though not as dramatic.

  5. #5
    Senior Member 85_Ciera_Rebuild's Avatar
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    Quote Originally Posted by Sigurd Jarlson View Post
    ...tach in my 1988 Ciera 3.8L FE3 coupe is off by a factor of at least 2 or 3...
    A 1989 digital odometer did the same thing, until it stopped at 300k miles.

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