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Thread: Fuel gauge ...back at it again

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    VCVC Member garagedoordennis's Avatar
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    Fuel gauge ...back at it again

    Has anyone successfully had a new vans tank and 30ohm sending unit work? 1st Gen of course.....
    1968 Chevy 90 250/700r/Fuel Injected - sold and missed
    1966 Chevy handyvan 350/auto (work in progress)
    1965 GMC 350/auto ( just had to have )

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    Fuel Guage

    I have not ...
    but what problem are you having? I maybe able to advise on testing an installed unit.
    Gary
    1965 Display

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    VCVC Member garagedoordennis's Avatar
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    When testing the sending unit with an ohm meter i can get a 20-30 ohm movement white bouncing the van around. I have tried 3 different factory gauges , tested the wire from the drivers side tail light ( plug ) to the dash, checked the ground ( factory location) added a ground to the tank ( just checking...) and no luck. Ive been just topping it off last summer and the one time out this year so i know im starting out full...and just paying attention to miles. This last time out it just reminded me looking down at the gauge ( "im still not working ").............
    1968 Chevy 90 250/700r/Fuel Injected - sold and missed
    1966 Chevy handyvan 350/auto (work in progress)
    1965 GMC 350/auto ( just had to have )

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    Fuel gauge ...back at it again

    It would be good to separate the problem gauge or sending unit issue (and their related wiring).

    I suspect since you replaced three gauges (wiring check?) a good start would be on the sending unit end.
    Two ways to check the sending unit with it still installed (save labor). Either by adding fuel to the tank or pumping out the fuel (electric fuel pump)

    The same white connector/ tan wire near the LR tail light you reference, disconnect that connection & hook one lead from an ohm meter to the fuel tank side of the connector. Hook the other ohm meter lead to the sending unit ground (factory location is near the RR tire, inboard side of the frame).

    Now your choice
    a) drain the fuel tank (electric pump?) and monitor the amp meter: Full tank = ~ 30 ohms, 1/2 full = 15 ohms & empty = 0 ohms. You should see a constant decreasing ohm values with no discontinuities in the readings.
    b) conversely slowly fill the tank and monitor the amp meter: Empty fuel tank = 0 ohms, 1/2 full = ~15 ohms & full roughly = 30 ohms. You should see a constant increasing ohm values with no discontinuities in the readings.

    To state the obvious - filling is an easier logistic - but if the sending unit is faulty then you have to drain the tank to repair...
    Last edited by gfleduc; 04-16-2021 at 06:11 PM.
    Gary
    1965 Display

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    VCVC Charter Member Vanner68's Avatar
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    This is probably not what you want to hear, but here goes:

    Every time I have a fuel gauge issue, I bite the bullet and drop the tank.

    Remove the sender, remove the gauge and bench test with clip leads and a battery. Verify that those two items are functioning flawlessly If there is anything but a smooth reaction on the bench, you are going to have problems in the van.

    The sender can be tested with an ohm meter. Use an old analog (needle type) if you have one. Look for a smooth reaction.

    The gauge can be tested with, of all things, the dimmer part of a headlight switch. It's not perfect, but pretty close to the rating of the sender.

    If everything passes a bench test, then it's time to dig into the wiring. All connectors are suspect, remember an open circuit makes the gauge go to full and a short circuit makes it go to empty.
    Gregg Groff


    There's no place like 127.0.0.1

    1968 Chevy G20 108 panel Now with 454 power!

    1965 Chevy G10 panel- OHC Pontiac inline 6

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