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550 speedometer jumping up and down

Discussion in 'Technical Q&A' started by AndersJL, Nov 29, 2005.

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  1. AndersJL

    AndersJL Formula Junior

    Apr 16, 2001
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    AL
    #1 AndersJL, Nov 29, 2005
    Help, my 550 speedometer is jumping up and down (when going at constant speed, so it isn´t me playing with the accelerator...)
    The problem only occurs when the engine has reached full temp. Could it be a potentiometer ? If so, where is it located (pics.) ?
     
  2. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
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    Malcolm W
    #2 Ferrari_tech, Nov 29, 2005
    Not sure about this (I will have to check), but I think it gets it's signal from the ABS electronic control unit.

    Have you had any ABS warning lights come on ?
     
  3. AndersJL

    AndersJL Formula Junior

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    #3 AndersJL, Nov 29, 2005
    No (not yet...)
     
  4. Ferrari_tech

    Ferrari_tech Formula 3

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    #4 Ferrari_tech, Nov 29, 2005
    Just had confirmation - the speedo does get it's signal from the ABS ECU
     
  5. AndersJL

    AndersJL Formula Junior

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    #5 AndersJL, Nov 29, 2005
    Hmmmm, so, it the ABS is (supposingly) working, could it be a cable that is struggling / oxide ? Where is this ABS ECU unit located ?
     
  6. PapaiK

    PapaiK Formula Junior

    Mar 5, 2005
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    Kyle
    #6 PapaiK, Nov 29, 2005
    My dad has the Same problem in his 70' MGB :p
     
  7. Ferrari_tech

    Ferrari_tech Formula 3

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    #7 Ferrari_tech, Nov 29, 2005
    Sorry don't know where it's located, but the best thing to do is to get the car to your dealer who will test the system on the SD2 and hopefully trace the fault - it could just be a poor connection at the ECU or a wheel sensor connection.
     
  8. plugzit

    plugzit F1 Veteran
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    Bruce Bogart
    #8 plugzit, Nov 29, 2005
    When mind did that, I found that one of the wires from the speedo sensor was cracked and the wire broken, sometimes breaking contact.
     
  9. Frari

    Frari Formula 3

    Nov 5, 2003
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    tony
    #9 Frari, Nov 29, 2005
    Sorry but must ask, is it on a bumpy road?
     
  10. AndersJL

    AndersJL Formula Junior

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    #10 AndersJL, Nov 30, 2005
    Yepp, that´s the case! Thinking back on when / where it mostly happens, it strucks me that you are right. It does happen on the FWY, but mostly on smaller roads. -Anyone knows where the cables are located ?
     
  11. plugzit

    plugzit F1 Veteran
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    #11 plugzit, Nov 30, 2005
    the sensor is located on the transmission. two wires come out of it. usually the break is where the wires exit the sensor.
     
  12. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
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    #12 Rifledriver, Nov 30, 2005

    The ABS system provides the signal Just as Malcom said, and it is distributed to many systems. There is no speedo signal from the trans on a 550.
     
  13. AndersJL

    AndersJL Formula Junior

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    #13 AndersJL, Nov 30, 2005
    Hmmmm (again)....
    Many thanks for your input. I guess I have to leave the car to the authorised garage then. Not a do-it-your-self, save a buck kind of thing.
     
  14. dapper

    dapper Formula Junior

    Nov 10, 2003
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    #14 dapper, Nov 30, 2005
    My 348 speedo does the same, only when up to working temp, needle drops completely sometimes then wavers about a bit, then comes good again. None of this happens when getting to normal working temp. Guess its also ABS derived signal? I'll have to dig out the WSM and have a look. Another one to add onto the list for when engines out.
     
  15. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    Phil Hughes
    #15 ferrarifixer, Nov 30, 2005
    The speed signal originates from the rear wheel speed sensors....

    jack up the rear and drive it with the wheels off the ground to prove it.

    I'd check the rear wheel speed sensors, wheel bearings, and connections.
     

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