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Fuel gauge stuck on full...

Discussion in '308/328' started by PA PETE, Nov 7, 2021.

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  1. PA PETE

    PA PETE Rookie

    Oct 9, 2021
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    New Jersey
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    Peter Bailis
    #1 PA PETE, Nov 7, 2021
    OK, this is going to seem boring for some and most likely well covered but I am going to throw it out there anyway... 1982 308 GTSi fuel gauge stuck on full. Goes to empty with key off. Sending unit removed, cleaned, ohm meter shows proper readings through full range of float motion. Low fuel light works as designed. Checked for continuity on purple wire on tank to plug under steering column... no continuity... used jumper from sending unit to gauge... still sticks on full... any ideas??????
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,785
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #2 Steve Magnusson, Nov 7, 2021
    Last edited: Nov 7, 2021
    Your OM schematic shows three wires at the fuel sender: Z (purple) to the gauge; RN (red/black) +12V with key "on"; and an unlabeled ground wire (probably black). I'd make sure the ground wire is really at ground -- i.e., do something like add a jumper from the terminal at the sender with this ground wire to a known good ground to ensure it really is ground (pretty sure this is a simple voltage divider circuit arrangement so if the ground is lost, the Z wire going to the gauge will always be at +12V regardless of where the float is).

    (Your report of no continuity on the Z wire from the sender to the gauge is some concern, but, if you jumper that, too, that should take it out of the equation even if bad).

    ....and another first post -- my F has a problem -- happens a lot ;)
     
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  3. PA PETE

    PA PETE Rookie

    Oct 9, 2021
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    Peter Bailis
    #3 PA PETE, Nov 8, 2021
    Thanks Steve for your reply and ideas... found open in violet wire and repaired... now have 12V at sending unit until I plug in the wire to the terminal on the unit... voltage drops to 4V but the gauge still reads full (believe I have approx. 3/4 to 2/3 of a tank of fuel in the vehicle)... I'm fairly sure the ground is good because the low fuel light works as designed... I will continue to plug away at it... any other ideas will be REALLY appreciated.
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,785
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #4 Steve Magnusson, Nov 8, 2021
    Always possible the gauge itself has an internal flaw.
     
  5. PA PETE

    PA PETE Rookie

    Oct 9, 2021
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    Peter Bailis
    #5 PA PETE, Nov 8, 2021
    Ha ha... Yea, I have thought that but wanted to go through the other systems first... tomorrow is another day... I will keep at it until I get it.
     
  6. mike996

    mike996 F1 Veteran

    Jun 14, 2008
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    Mike 996
    #6 mike996, Nov 9, 2021
    "Always possible the gauge itself has an internal flaw."

    Or the tank is full. :p
     
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  7. PA PETE

    PA PETE Rookie

    Oct 9, 2021
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    Peter Bailis
    #7 PA PETE, Nov 25, 2021
    After disassembling the fuel sending unit and cleaning all the contacts and the steel bar the float assembly is attached to then reassembling the unit with new stainless nuts and bolts... an ohm meter disclosed that my sending unit was now operating as designed. So, I concentrated my efforts on the gauge... upon removing the gauge from the instrument panel I heard a tiny "snap" and discovered the fuse for that circuit had popped... checking all the internal circuits on the gauge (of which there are only 3, the low fuel light, the gauge light and the gauge itself) I found the gauge circuit (green wire) had a dead short. Found a good gauge on line for X amount and installed... fuel gauge problem fixed. I disassembled the old gauge and found what seems to be what looked like a resistor and failed (broken in two), I am still trying to figure out how this failed internal part could have caused a dead short... perhaps it is a diode ? Anybody have any thoughts on this or better insight as to what the little electrical device is??? Thanks to all who offered advice on this.
     
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  8. BigTex

    BigTex Seven Time F1 World Champ
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    Dec 6, 2002
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    Bubba
    #8 BigTex, Nov 27, 2021
    Good job getting ot sorted out, welcome.
     
    PA PETE likes this.
  9. PA PETE

    PA PETE Rookie

    Oct 9, 2021
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    Peter Bailis
    #9 PA PETE, Dec 14, 2021
    Thank you Big Tex... just took my time and my old mechanics brain.
     

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