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Fuel Gauge Reading Off

Discussion in 'Intermediate CJ-5/6/7/8' started by Josephkerr, Nov 27, 2020.

  1. Nov 27, 2020
    Josephkerr

    Josephkerr New Member

    Georgia
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    Nov 17, 2019
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    On a full tank gauge reads full after a.few.days of driving it will rapidly run down to half a tank at that point when I gas up it was actually at a 1/4 tank. I've read people say that ethanol has can cause this? What say you
     
  2. Nov 27, 2020
    zila

    zila I throw poop

    Rock Springs,...
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    I say your fuel gauge needs calibrated
     
  3. Nov 27, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Make sure all the wiring connections are tight and clean. The reading is regulated by resistance in the circuit.
     
  4. Nov 27, 2020
    ToddsCJ

    ToddsCJ Phantom Phixer

    Williams, Arizona
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    Yeah, if you leave it stand too long at a 1/4 tank or so it would gum it up pretty quick, but I would bet ya need to pull the sending unit and calibrate it to your gauge. Be sure you have a good ground on the sender, and the gauge.
     
  5. Nov 27, 2020
    zila

    zila I throw poop

    Rock Springs,...
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    FWIW my gauge is off. It is too much hassle to fix it. I hate dropping the tank
     
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  6. Nov 28, 2020
    sterlclan

    sterlclan Member 2022 Sponsor

    exploring the...
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    Mine hasn’t worked in a few years have the sender to fix but nah.
     
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  7. Nov 28, 2020
    mrtii

    mrtii 1972 cj51986 cj7 2022 Sponsor

    gilroy, California
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    It is most likely the sending unit and poor ground connection
     
  8. Nov 28, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Year, model, equipment? It's important. All we can assume is that you own an intermediate or later Jeep, since you posted in that forum. No such info in your post, signature, or profile.

    There's no fuel gauge "calbration" per se.

    The inaccuracy could be in the gauge (less likely) or in the sender (more likely). Suggest you read this thread - Build A Gauge Tester - for some background. You don't need to build the tester, but the testing methods used will apply.

    You could also read the TSM for your year ... whatever year that is! :confused:

    To me, the ethanol idea seems extraordinarily unlikely. The density of the gas will change when ethanol is mixed in, and that could affect how high the float in the tank sits on the surface of the gas. This effect will be very very small, if measurable. Also possible that the ethanol would attack a plastic float in the tank, but then the float would sink, and that's backwards from the high reading that you see.

    Cleaning the connections is always a good idea, but the most likely problematic connections are on top of the fuel tank (assuming you own an intermediate or later Jeep), and a pain to get to. See Zila's and Jeff's post above.
     
    Last edited: Nov 28, 2020
    Rugerhound likes this.
  9. Nov 28, 2020
    bigjohn

    bigjohn Active Member

    Kelso Wa
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    If you have a semi functioning Guage you're ahead of most, haha. Your ohm capable multi meter is your friend. Id start under the dash to see if you're getting correct readings. If I recall the pink wire to your fuel gauge is the sender. 10 ohms is full, 25 is half, around 70 is empty if my memory is correct. If the ohm reading and gauge match, move to the sender. You'll not love dropping the tank. Run it as close to empty before hand. Last time I dropped the tank I thought I was nearly empty. It was still over half full. :banghead:
     
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  10. Nov 28, 2020
    zila

    zila I throw poop

    Rock Springs,...
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  11. Dec 4, 2020
    Josephkerr

    Josephkerr New Member

    Georgia
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    Your not gonna believe this i filled up my tank the other day with non ethanol and the gauge is reading acurately
     
  12. Dec 4, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    I don't believe it.

    We need a scientific hypothesis to peer review.
     
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  13. Dec 4, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I believe it happened, but I don't believe ethanol is the reason.

    Anecdotal. Provocative but not proof, could be coincidence. In most cases the rationale comes before the proof, not the other way. Otherwise you're just randomly testing stuff and hoping to discover something (like alchemy).
     
    Last edited: Dec 4, 2020
  14. Dec 4, 2020
    zila

    zila I throw poop

    Rock Springs,...
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    Mine is accurate after a fill up every time. Always reads "Full" It's around half a tank where things go sideways.
     
  15. Dec 4, 2020
    Boyink

    Boyink Super Moderator Staff Member

    Tulsa, OK
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    The most accurate Jeep fuel gauge I ever had was a wooden stick kept next to the driver's seat.
     
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  16. Dec 4, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I think the gauges are generally ok (except for the goofy CVR part), but the senders in the tanks seem to be both inaccurate and fragile/unreliable. Plus the aftermarket senders are a genuine roll of the dice. If you get a replacement sender, test it for reliable and accurate operation with your multimeter before it goes in the tank.
     
  17. Dec 4, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Me too, and I can do it from the driver's seat. It's big improvement over using a lit match to peer into the tank.

    (Model T Ford owners often had commercially produced rulers graduated in gallons for each style of tank.)
     
  18. Dec 4, 2020
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    My Jeep had this problem - the easiest fix I could devise was to run a wire from one of the sending unit mounting screws (through the same sheath the sending unit wire runs in) to the firewall up behind the dash, where it's grounded. The fuel gauge still doesn't read super accurately, but at least it now provides some indication that there's gas in the tank.
     
    Last edited: Dec 4, 2020
  19. Dec 4, 2020
    Downs

    Downs Rattlecan All The Things!

    Hunt County Texas
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    This is no kidding. I made sure to test my replacement out as well as I could. Found the wiper arm wasn't making contact right and the ohm readings were all over the place. Put more of a bend in the wiper arm which put more pressure on the little nub that rides on the coil. Now I get smooth and mostly accurate fuel readings.
     
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  20. Dec 4, 2020
    baldjosh

    baldjosh Member

    pacific north west
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    Yardstick here...
     
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