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Fuel gauge stuck on full

Discussion in 'Tech Discussion' started by thecantaloupeman, Jul 15, 2019.

  1. Rickf

    Rickf Full Access Member

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  2. thecantaloupeman

    thecantaloupeman Full Access Member

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    So I just went out yesterday to check the fuses, and noticed the gauge was a little bit above 3/4 of a tank. When I went to turn the key on though, it was back at fully horizontal and past full. The gauge seems to slowly go down after a while with the car turned off. Anyway I replaced the gauge cluster fuse and it didn't do anything. It was worth a shot though. I still am not sure how to check my ground wire though.

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  3. thecantaloupeman

    thecantaloupeman Full Access Member

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    The main thing though is that I don't know how to check my ground wire. It is very hard to see in between the bed. Is there any way I can test the ground up front maybe?

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  4. DanMcG

    DanMcG Supporting Member Supporting Member

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    You should be able to feel around for the ground wire. the ground wire goes from the sending unit to the top of the frame rail, fastened right next to the tank. I'll see if I got a pic.

    well I just tried to see on my truck but due to some surgery I can't get under the truck. but there's only two wires on the sending unit, one goes into the harness and the other one is your ground. wiggle it and see if connected at both ends. then have someone watch the gauge when you're moving it, to see if it affects the gauge.
    hope this helps.
     
    Last edited: Jul 20, 2019
  5. thecantaloupeman

    thecantaloupeman Full Access Member

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    Thanks Ill give that a shot tomorrow morning!
     
  6. Rusty Nail

    Rusty Nail makes people uncomfortable Supporting Member

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    LUCKY DOG! ... Must be nice!
     
  7. thecantaloupeman

    thecantaloupeman Full Access Member

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    Hahahaha. Well quick update this morning I drove to the gas station and the gauge seemed to be working for about 5 mins. It was on half a tank and was bouncing around. 1/2 tank sounds about right. I went to turn it off and fill the tank, and now it's stuck past full again. When I turned it off it stated on half a tank. Until I started it again and it shot past full. Now it keeps slowly going down until I turn the key on again.

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  8. Rusty Nail

    Rusty Nail makes people uncomfortable Supporting Member

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    Sounds easy enough!
     
  9. bedwards

    bedwards Full Access Member

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    Mine goes well past full when full
     
  10. thecantaloupeman

    thecantaloupeman Full Access Member

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    Well that's the thing. When the key is off for a while, the needle slowly falls. When you turn it on, it goes right back past full. It was working this morning for 5 mins. It said half tank which was right because I put 10 gallons in. When I was filling it the needle wasn't moving either. When I turned it on though it went past full again. I drove it quite a ways and it didn't seem to go down. How do I find the ground wire underneath the car? Also isn't the gauge supposed to read empty when it's turned off?

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  11. thecantaloupeman

    thecantaloupeman Full Access Member

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    Is there a way to test my ground connection using my voltmeter? I looked around and still haven't found where the ground wire leads. I know where it is on the sending unit, but can't reach it or see it very well, and I looked around and can't find where that wire leads to.

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  12. Frankenchevy

    Frankenchevy . Supporting Member

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    The gauge stays where it last was when the key is turned off in my truck. It does not fall to E.

    Look at your bulkhead connector at the firewall. There are 3 ‘plugs’. The largest one closest to the center of the vehicle has a pink wire at the bottom—pink 30. Make sure it’s in good shape from there back to the tank sender—where the fuel lines and wires connect to the tank. You should be able to see it in the gap between the cab and bed.

    The ground may be between the tank and frame rather than on top of the frame. Look for bolt threads inside the frame rail for reference.
     
  13. Dave 84

    Dave 84 Supporting Member Supporting Member

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    A fuel sender wire that is open (cut or not connected) will read full tank a shorted to ground will read empty so so find that wire and ground it if it goes to empty your gauge is good you can also ohm the sender chevy is 0 to 90 ohms o witch would be full contact with ground will be empty 90 or higher will be full
     
  14. DanMcG

    DanMcG Supporting Member Supporting Member

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    Question for someone who knows, I don't think the sending unit is isolated, so if the tank shows it's grounded wouldn't the sending unit also be grounded? So instead for trying to get to the ground wire, just check continuity of the tank to confirm ground?
     
  15. 75gmck25

    75gmck25 Full Access Member

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    There is a rubber ring between the sending unit and the tank body, so the sending unit should be electrically isolated from ground. The sending unit body has a flat ground tab on it, and the ground wire may be soldered on or pushed on to the tab. The attached ground wire is about 12-18" (maybe) long. For the sending unit wire there is a threaded post sticking up and the sending unit wire plug pushes onto the post (despite the threads, it does not screw on).

    On my truck the ground wire comes down from the tank and through a grommet in the frame rail, and is grounded to a screw that is easy to access inside the frame rail. The sending unit wire comes through the same grommet, and there is a round pull-apart plug in the wire just inside the frame rail. When you remove the tank you take the ground screw out and pop apart the plug in the sending unit wire so that the tank can be removed with the wires still connected to the sending unit.

    Bruce
     
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