Tach goes down instead of up ?

Posted by Big Red 211, Dec 4, 2004

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  1. Big Red 211

    Big Red 211 Proven Member

    Joined Dec 10, 2002
    On my 90 TSI I just swapped the ECU with one from a 93 TSI cause a cap burnt on the 90 ECU. After I installed the 93 ecu the tach will go down when I'm accelerating then it levels off when I take my foot off the gas. Before with original 90 ecu the tach would jump around (about 100-200rpm) at any engine speed. It did that all the time and I'm guessing that's why the 90 ecu burnt up.
    The car runs fine. The tach just isn't working right. Also I did switch the 2 wires at the ecu terminals.

    Anyway, if anyone knows why my tach is going the wrong way please lmk, I don't want to burn up another ECU.


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  2. sjgYFZ200

    sjgYFZ200 Proven Member

    Joined Jun 25, 2004
    Albany, New York
    isnt it true that very early ECU's cant be used with later ones?
  3. i1nk83

    i1nk83 Proven Member

    Joined Dec 30, 2003
    dothan, Alabama
    you are going to have to go and find either a 91+ tach/cluster or swap back in a 90 ecu
  4. Big Red 211

    Big Red 211 Proven Member

    Joined Dec 10, 2002
    Damn, I never heard about that before. I guess I'll have to get my old one fixed.
  5. jott5555

    jott5555 Proven Member

    Joined Apr 10, 2003
    salem, Oregon
    another thing to check that can mess with your tach is a small "noise filter" it was only on 90's its on the drivers side of the intake manifold. the connection is very close to where the knock sensor connects. its a small 1in x .5in silver box with i beleive 2 wires comming out of it..

    now from satan this little trinket is over 50 dollars i beleive. if you know anyone in the area that has a 90 dsm bum his or hers plug it in and see if you still have a problem.
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