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HELP!!! Speedometer trouble

Discussion in '348/355' started by junkyarddog, Jun 7, 2007.

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  1. junkyarddog

    junkyarddog Formula Junior

    May 18, 2006
    353
    Palatka, FL
    Full Name:
    Kelly Lake
    #1 junkyarddog, Jun 7, 2007
    I thought I had this fixed but I was wrong. My speedometer randomly goes completely around while I'm driving and sticks racking up miles. It's calculating correctly I'm just not going that fast. I checked all the wiring behind the speedo and it looks good everything is real tight. I haven't checked the sending unit yet simply because if I give it a smack on the gauge console when it's in error mode it will go back to normal. This is very annoying and I'm not sure what to do. I'd hate to buy a new speedo to find out it is something else. Any suggestions? Thanks in advance.
     
  2. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,620
    The Brickyard
    Full Name:
    The Bad Guy
    #2 ernie, Jun 7, 2007
    Check the sending unit before you get a new speedo. I wouldn't be surprised if you found a busted wire. Or, the sending unit could be shot.
     
  3. No Doubt

    No Doubt Seven Time F1 World Champ

    May 21, 2005
    72,740
    Vegas+Alabama
    Full Name:
    Mr. Sideways
    #3 No Doubt, Jun 7, 2007
    #1. Swap the left and right engine ecus behind your seats. Only one ecu sends your speedometer its signal, but both have the same capability of sending that signal. That's free and quick (however, I may be thinking about the tach signal, so this may not help you....won't hurt anything to try, though).

    #2. Remove the two phillips screws that flank the bottom of your black driver's gage console. Lift up your console, turn it around, and verify that your plastic-covered electrical snap connections are all seated.

    Better yet, spray into each connection first with contact cleaner, and then dab in Stabilant 22a. Not quite so quick as swapping ecus, and the Stabilant 22a is pricey.

    #3. If the above two things fail to solve your problem, then replace your sending unit. Wait on mail-order part (probably) and pay for a Ferrari OEM replacement.

    #4. If the above three things fail to solve your problem, then you will probably need to repair or replace your speedometer. Not cheap. Not quick. (but at least it is easy to physically swap out with a good unit)
     
  4. Miltonian

    Miltonian F1 Veteran

    Dec 11, 2002
    5,966
    Milton, Wash.
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    Jeff B.
    #4 Miltonian, Jun 7, 2007
    What do you mean when you say "It's calculating correctly"?

    If the sending unit goes bad, the speedo needle will go up and down at random, and the odometer will show that you are putting on more miles than you are actually driving. For instance, the needle reads 150mph when you are doing 60mph, and the odometer adds up the miles as though you are actually driving 150mph.

    If the odometer reading seems to be correct, but the speedo needle is reading wacky, then it's your speedo, not the sending unit. The speedo should be repairable.

    What did you do when you "thought you had it fixed"?
     
  5. junkyarddog

    junkyarddog Formula Junior

    May 18, 2006
    353
    Palatka, FL
    Full Name:
    Kelly Lake
    #5 junkyarddog, Jun 7, 2007
    BY calculating correctly I meant that it was reading over 200mph and the odometer was rolling as it should if I were doing that speed. The car has done this too me before but I unplugged it, cleaned it, and reconnected it and it worked for awhile with no trouble. I just checked the sending unit and it looked ok. For safe measure I disconnected it and cleaned everything. I also just got done recleaning the connector that plugs into the speedo. I was able to get it to fail with a whack before I cleaned it. Right now it appears to be working ok. I'm going to get some of the Stabilant 22a hopefully that will be the all cure.
     
  6. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,620
    The Brickyard
    Full Name:
    The Bad Guy
    #6 ernie, Jun 7, 2007
    I still say it's the sender.

    The seal on the tip of the sender gets dry and allows oil to get inside it pats the magnet. So even though it looks fine on the outside, and the wires are all in good shape, it could have oil inside of it goofing up the circuitry. But, do try the Stabilant 22a first.
     
  7. Miltonian

    Miltonian F1 Veteran

    Dec 11, 2002
    5,966
    Milton, Wash.
    Full Name:
    Jeff B.
    #7 Miltonian, Jun 7, 2007
    Sure sounds like a typical sender problem.
     

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