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Thread: Fuel gauge not working. Help!

  1. #1
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    Fuel gauge not working. Help!

    I don’t know what else to try.

    Sensor works (16 ohms at mt, can get up to 250 ohms when up). 6.6v at the sensor (not sure what voltage the gauge sends to it so maybe that’s it?) and good ground. I have 12v and ground at the gauge. It should work but is stuck on MT no matter where i move the float. Oh, and the sticker says it’s for that ohm range sensor also. Help!
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

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  2. #2
    Senior Member edwardb's Avatar
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    The usual Ford sender doesn't use voltage to the gauge. It's just a variable resistor, like a volume control or whatever. The gauge strictly reads ohms. The standard range for the Mustang sender used in Roadsters, which I'm familiar with, is in the 16 (empty) to 158 ohms (full) range. Yours might be different. Just confirm what it's supposed to be. You should be able to read the ohms at the sensor itself by putting a multimeter across the terminals and moving it through its travel. Also at the wires where it's attached to the speedo, which would confirm the harness is working properly. I'm assuming you've followed the instructions for calibrating your gauge to the ohm range of your sender? That would also confirm its powering up properly.
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  3. #3
    Papa's Avatar
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    Assuming you have the Speedhut gauges, as Paul said you need to be sure the calibration matches your sender. For the typical Ford sender, you need to run the calibration cycle until your fuel gauge is at 7/8.

    Dave
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  4. #4
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    I am running the auto meter gauges and the gauge is supposed to be for the sender. It’s marked 16-158, and that’s very close to what I measure ohms on the sender. The gauge cannot be calibrated like the speedhut gauges. (FWIW, these are temporary to run and test it).

    The gauge has to send an electrical signal in order to measure ohms. A known voltage, measure the current and ohms are derived. I have a voltage, I have ohms so why isn’t it reading? I will unplug and check the wires from gauge to sender just to make sure when next in the shop.

  5. #5
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    i had very very similar issue and what it turned out to be was the plug that snaps onto the sending unit, just did not make a good connection. Ended up removing the plastic holder on the female plug and snaping the wires on each prong, then held them in place with silicone.

  6. #6
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    Are you sure the gauge is good?
    Quick test for the AutoMeter gauge.....
    Connect the gauge to +12 and ground at the terminals on the gauge, the needle should go to F with nothing connected to the sensor terminal.
    Now connect the sensor terminal on the gauge to ground, the needle will now go to E.
    If the above works then the gauge is good.
    Last edited by JimLev; 08-25-2018 at 08:39 AM.

  7. #7
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    Quote Originally Posted by duff33 View Post
    i had very very similar issue and what it turned out to be was the plug that snaps onto the sending unit, just did not make a good connection. Ended up removing the plastic holder on the female plug and snaping the wires on each prong, then held them in place with silicone.
    I had also tried connecting the wires straight to the pins and it didn’t work.

    Quote Originally Posted by JimLev View Post
    Are you sure the gauge is good?
    Quick test for the AutoMeter gauge.....
    Connect the gauge to +12 and ground at the terminals on the gauge, the needle should go to F with nothing connected to the sensor terminal.
    Now connect the sensor terminal on the gauge to ground, the needle will now go to E.
    If the above works then the gauge is good.
    With nothing connected to the gauge, ie power on but plug disconnected, the gauge stays on E. Even then you turn the key on, it never moves from E. I will play with it and remove the sensor wire also, to make sure, but judging from what you say, it sounds like the gauge is bad. Which is where I was starting to lean anyway. I’d like to see it work (everything work) before I start swapping out the temp parts with my permanent parts later on.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

  8. #8
    Senior Member Big Blocker's Avatar
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    Any chance this gauge just needs the "Ol Engineers Tap" done to it?? My fuel gauge (Autometer Classic Cobra) sticks on E until I tap the glass three times, then it works perfectly until the next time I start the car . . . I always figured that when I shut down the car, the needle pins itself so hard to E that the next time I need to jar it loose.
    Wouldn't be the first time that someone has chased a mechanical problem thinking its electrical.

    Doc
    Last edited by Big Blocker; 08-25-2018 at 01:32 PM.
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  9. #9
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    Well, Doc, I haven’t tried it but I certainly will.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

  10. #10
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    Quote Originally Posted by Svtfreak View Post

    With nothing connected to the gauge, ie power on but plug disconnected, the gauge stays on E. Even then you turn the key on, it never moves from E. I will play with it and remove the sensor wire also, to make sure, but judging from what you say, it sounds like the gauge is bad. Which is where I was starting to lean anyway. I’d like to see it work (everything work) before I start swapping out the temp parts with my permanent parts later on.
    Are you sure you have 12 v at the gauge? Without it present it won't work.
    My gauges aren't wired to the car yet, I use some jumper leads to connect the gauge to a spare battery to test it.

  11. #11
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    Absolutely positive I have 12v at the gauge and good ground.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

  12. #12
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    OK, last test....(meter lead polarity doesn't matter)
    From the S to Grd terminals should read ~112 ohms.
    From the I to Grd terminals should read ~205 ohms.
    From the S to I terminals should read ~94 ohms.

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  14. #13
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    Quote Originally Posted by Big Blocker View Post
    Any chance this gauge just needs the "Ol Engineers Tap" done to it?? My fuel gauge (Autometer Classic Cobra) sticks on E until I tap the glass three times, then it works perfectly until the next time I start the car . . . I always figured that when I shut down the car, the needle pins itself so hard to E that the next time I need to jar it loose.
    Wouldn't be the first time that someone has chased a mechanical problem thinking its electrical.

    Doc
    Well, this is exactly what did it. A good old tap and it started working just right. Thaanks!
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

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