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Thread: Speedometer jumping around...What gives?

  1. #16
    Join Date
    Jul 2003
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    Ottawa, Ohio
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    5,415
    Thats not the speed sensor.
    SCCoA Member#: 2515
    1990 SC AOD 2.1L Kenne Bell
    11.676 @ 121.35 mph
    506hp/478tq
    My Garage

  2. #17
    Join Date
    Jul 2009
    Location
    Mooresville, IN
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    120
    Yea i know i thought it plugged into the sensor that goes into the transmission. There is like a circular hole in the piece that it looks like it goes in but it cant.

  3. #18
    Join Date
    Jul 2009
    Location
    Mooresville, IN
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    120
    Here is a picture of my old speed sensor. I thought it went where the yellow piece is but there is no way to screw the threads on that are on the cable.
    Attached Images Attached Images  

  4. #19
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    Ottawa, Ohio
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    Nothing plugs into that yellow piece, just the 2 wire sensor plug.
    SCCoA Member#: 2515
    1990 SC AOD 2.1L Kenne Bell
    11.676 @ 121.35 mph
    506hp/478tq
    My Garage

  5. #20
    Join Date
    Jul 2009
    Location
    Mooresville, IN
    Posts
    120
    Ok thanks. I just didnt know if maybe I broke something off that cable that I thought went in there or not.

  6. #21
    Join Date
    Jul 2017
    Location
    Northern Virginia
    Posts
    35

    Speedo sits at 125

    This is an old thread, but it has the best pictures of the likely problem part.

    A few months after buying my 89 5-spd, the speedo pegged to 125 while I was driving it. A couple days later it worked fine, then went out again while driving it. Now is just pegs to 125 at start up and sits there.

    I have already had the IC out for previous issues and I'm confident all the connections are good. The odometer is still working as well, or at least it is still turning and seems accurate for the mileage I have driven since the problem, which is very low. Overall the car has 70K miles, no rust, and is very clean.

    My best guess is the speed sensor has gone bad. I have found the replacement sensor at Rock Auto. I'm wondering how hard it is to change out, and how I get at the sensor. I am not a mechanic, but willing to learn and give it shot before taking it in to my local shop. I'm also wondering what the likelihood is that the plastic gear inside the trans is the problem. That would probably be a real pain to fix.

    Given I won't be driving the car much until spring, I have time to sort this out. It's no fun to drive without a speedo. The GPS readout on my traffic app keeps me out of trouble, but it's just not right to look down at an unmoving speedo.

    Thx,
    MP

  7. #22
    Join Date
    Dec 2007
    Location
    Pacific Rim
    Posts
    6,721
    One wiring connector and one bolt on the clamp/retainer. The connector is aged, so be gentle with the ears so you don't snap them off.

    Unless it's gummed up and chemically welded, it should pop out with a slight twist/pull, I'd think. Have the new one ready in case fluid tries to escape. Pay attention to the orientation so you don't have to fight the connector going back on.

    Good luck, but if it were me, I'd suspect the gears in the speedo head first. Is the trip meter stuck on 0000?

  8. #23
    Join Date
    Jul 2017
    Location
    Northern Virginia
    Posts
    35
    Quote Originally Posted by KMT View Post
    One wiring connector and one bolt on the clamp/retainer. The connector is aged, so be gentle with the ears so you don't snap them off.

    Unless it's gummed up and chemically welded, it should pop out with a slight twist/pull, I'd think. Have the new one ready in case fluid tries to escape. Pay attention to the orientation so you don't have to fight the connector going back on.

    Good luck, but if it were me, I'd suspect the gears in the speedo head first. Is the trip meter stuck on 0000?
    The odometer and trip meter are both working. I don't see anything in the Ford shop manual or pics of the odometer gears that indicates they are connected to the speedo. The EVTM troubleshooting guide just says to replace the speedo, which I would rather not do unless it's the only option. Of course if the odometer is working that would seem to indicate the speed sensor is sending a signal, so that isn't a very likely fix either. I'm mostly guessing at a fix at this point.

    But replacing the odometer gears is good idea for preventative maintenance regardless, so I'll probably do that.

    Thanks,
    MP

  9. #24
    Join Date
    Jul 2002
    Location
    Roanoke, Virginia
    Posts
    3,293
    The sensor is held in with a single 10mm bolt if my memory is any good. You can get to the sensor pretty easily by jacking the car up mid door on the drivers side...no harder than changing a light bulb.

    -Tim
    Current Collection
    1994 Thunderbird SC - Auto converted to 5spd

    1995 Thunderbird SC - Auto

    1994 Thunderbird SC - 5spd
    1989 Thunderbird SC - 5spd - Daily Driver
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    1994 Thunderbird SC - 3v Project

  10. #25
    Join Date
    Jul 2017
    Location
    Northern Virginia
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    Quote Originally Posted by Tim Groth View Post
    The sensor is held in with a single 10mm bolt if my memory is any good. You can get to the sensor pretty easily by jacking the car up mid door on the drivers side...no harder than changing a light bulb.

    -Tim
    Thanks, that helps. I just wish I was confident this would fix the problem.

  11. #26
    Join Date
    Dec 2007
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    Pacific Rim
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    Quote Originally Posted by 91 Titanium View Post
    I just wish I was confident this would fix the problem.

    You can always just pull the connector, then live test to see if the speedo rests at zero instead of 125. If the head unit itself is borked, it shouldn't make any difference.
    Last edited by KMT; 02-04-2018 at 11:58 PM.

  12. #27
    Join Date
    Jan 2010
    Location
    Bossier City, LA
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    2,237
    There's a second part. The VSS signal drives the odo and the speedo off the same feed; if the odometers are working properly, most likely the VSS is OK and it's internal to the speedometer.

    Third part. Does the VMM, if so equipped, call for oil and filter changes early? That is, at say 1500 miles not 3000 miles? If it calls early, it may be a bad VSS or a bad shield in the wiring from there to the cluster; if not, again, the VSS is probably OK and it's in the speedometer.

    RwP

  13. #28
    Join Date
    Jul 2017
    Location
    Northern Virginia
    Posts
    35
    Thanks, I'll look at those options to narrow down the problem.

    The VMM hasn't called for any changes. I have put about 3000 miles on the car total, but only a couple hundred since the speedo went out.

    MP

  14. #29
    Join Date
    Jul 2017
    Location
    Northern Virginia
    Posts
    35

    New speedo fixed problem, but came with bad odometer

    Update:

    I decided the sensor must be good since the odometer was working just fine so I picked up a new IP. The speedo now works, but the IP came with a bad odometer. Plus the check gage light is on just for fun. No light with the original IP. I think I'll track down a new speedo for the original IP, upgrade the odometer gears, and put that IP back in. We'll see if that fixes everything.

    Of course now the heat and AC don't work, but that's a separate thread.

    MP

  15. #30
    Join Date
    Sep 2014
    Location
    Broken Arrow, Ok
    Posts
    196
    Mine jumps around when I'm stopped and even in park. Ill be sitting there and it will jump up to 100mph to as far as it will go. It doesn't work but the odometer still works.

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