fuel guage not accurate

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    Author Topic: fuel guage not accurate  (Read 1385 times)

    Offline thetex

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    • Posts: 59
    fuel guage not accurate
    « on: November 04, 2005 - 12:42:13 PM »
    Old topic I'm sure but I couldn't find it. My original fuel guage on 73 chally works OK but never reads full and shows empty when 1/4 tank left.  How do I correct this?      Thanks.
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    Offline Fred

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    Re: fuel guage not accurate
    « Reply #1 on: November 04, 2005 - 01:01:10 PM »
    I think that there is a ground strap from the fuel tank to the metal fuel line that is required.
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    Offline wiging19

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    Re: fuel guage not accurate
    « Reply #2 on: November 04, 2005 - 02:39:01 PM »
    I had the same problem on my guage.  I had to adjust the sending unit in the gas tank so it measured things correctly.  The tubes out of the sending unit and the electric connector to the fuel guage need to be parallel to the ground instead of at a 45 degree angle to the ground.  At least in my case.  The only thing I didn't like about fixing the problem is my gas tank leaked gas for a while afterwards until it sealed again.  At $3 a gallon it was a high point for me.  I just got the car back from the body shop from an accident and haven't had a chance to fill the tank to see if the shop put it back correctly.  I'll just have to check that while I'm fixing a pinion seal leak on my rear axle.  Of course not having the ground or a poor ground between your fuel tank & body would create this kind of problem too.
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    Offline MEK-Dangerfield

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    • I don't get NO respect! Member since 1/25/2002
    Re: fuel guage not accurate
    « Reply #3 on: November 04, 2005 - 03:00:10 PM »
    It's definitely a sending unit problem. They sit in gas, and it gets the worst of it over the years. Make sure you have less than a half tank when you take it out. I think all new sending units come with a new rubber gasket too, so that will help.

      Mike
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    Mike

    1970 Challenger - SOLD
    2016 SXT+.  1 of 524 SXT+'s in Plumb-crazy for 2016.

    Offline thetex

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    Re: fuel guage not accurate
    « Reply #4 on: November 05, 2005 - 07:19:03 PM »
    Thanks, I'll replace the sending unit.   
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    Offline GregGarner

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    • Posts: 18
    Re: fuel guage not accurate
    « Reply #5 on: November 07, 2005 - 09:09:49 PM »
    I would point out a couple of things:

    1) The sending unit is supposed to read 10 Ohms when the tank is full.

    2) The sending unit is suppose to read 78.5 Ohms when the tank is empty.

    3) The voltage regulator on the back of your instrument cluster can cause the gauges to read improperly, but it usually will
    effect the oil pressure and temperature as well.

    4) You can check the calibration on the fuel gauge itself by replacing the sending unit with a 10 Ohm resistor, and if it reads full scale (after a couple of minutes), then
    the gauge is OK and it is the sending unit that is the problem. Radio shack sells 10 Ohm and 80 Ohm resistors (Close enough to 78.5 Ohms).

    See these links for more information:

    How to calibrate your gauges:

    http://www.moparts.com/Tech/Archive/elec/8.html

    Grounding issues with fuel tank sending units:

    http://www.moparts.com/Tech/Archive/elec/31.html

    GregGarner
    www.rt-eng.com
    Home of the mopar tach and clock repair kit
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