1992 Ferrari Speedometer Sensor Problem | FerrariChat
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1992 Ferrari Speedometer Sensor Problem

Discussion in 'Technical Q&A' started by reklats, Jan 21, 2012.

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  1. reklats

    reklats Rookie

    Jan 14, 2012
    4
    #1 reklats, Jan 21, 2012
    I'm pretty sure I've got a problem with my speedometer sensor, because when I measure the resistance between the two leads from the sensor with an ohm meter, I get between 2.4 and 3.7 on the 200 milliamp scale. I've talked to Ricambi about pulling a new one off the shelf and putting an ohm meter across it, but they can't, or won't do it. I have no problem buying the part if I need it, but at $277.99, I would like to know thats it and I'm not just changing parts out. Ricambi did say they sell alot of them to replace the original ones. If anyone can help me with the spec's, I would appreciate it. Thank you.
     
  2. Iain

    Iain F1 Rookie

    Jan 21, 2005
    3,354
    UK
    #2 Iain, Jan 21, 2012
    What's the part number? I have a brand new one (and a working used one) for my 328 here. Think the part number I have is 116987
     
  3. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    13,673
    San Carlos, CA
    Full Name:
    Mitchell Le
    #3 yelcab, Jan 21, 2012
    This may be just semantic ...

    You measure resistance on the Ohm scale, not miliamp scale. If you were looking for resistance of the sensor, and you used the miliamp scale, then your reading is meaningless.
     
  4. jerry v

    jerry v Rookie

    Nov 15, 2010
    16
    #4 jerry v, Jan 21, 2012
    I checked mine and it is 3.6 ohms.
     
  5. Darolls

    Darolls F1 Veteran
    BANNED

    Jul 2, 2003
    7,782
    Full Name:
    Sparky
    #5 Darolls, Jan 22, 2012
    When the impulse generator starts to fail, it usually causes an intermittent failure (sometimes the speedo works; other times it doesn't!)

    If this is the case I'd say it's definitely the pick-up.

    $277 sounds excessive. The last 1 I bought was a 100 and some dollars; shop around.
     
  6. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    2,389
    Frederick, Maryland
    Full Name:
    Brian Brown
    #6 Motob, Jan 22, 2012
    You cannot just measure the resistance of the speedometer sending unit. It is not just a winding wrapped around a coil. It has a printed circuit board inside with an integrated circuit and other components. The only way to test it is to replace it with a known good unit.

    Brian B.
    Patrick Ottis Co.
     
  7. Miltonian

    Miltonian F1 Veteran

    Dec 11, 2002
    5,966
    Milton, Wash.
    Full Name:
    Jeff B.
    #7 Miltonian, Jan 22, 2012
    If it only seems to happen when you go over a bump, it could be a bad connection at the harnesss coupling. I'm not familiar with the Mondial T, but on the 348 this coupling is near the top of the left rear shock tower, in the engine compartment, and it joins the main wiring harness to drivetrain harness, and includes the wires for the speedometer, oil pressure and water temperature gauges and warning lights, and a couple of others. I believe there are seven or eight wires in it. If the connector is loose or damaged (wouldn't be the first one) then it may be losing continuity when you hit bumps. Worth a look. It's supposed to twist together firmly. By any chance have you noticed the oil or water gauges acting up at the same time as the speedo?

    Of course a failure of the sensor isn't uncommon.

    Good luck!
     

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