Why does fuel guage go from half full to...

Discussion in 'Fuel and Air Systems' started by MAPS, Mar 27, 2018.

  1. MAPS

    MAPS Well-Known Member

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    Hello
    I'd like some help with the experienced folks here, my guage sometimes (less and less lately) shows the proper fuel level and then at times, empty, back to the correct level (usually when I just start it) and then back to not working, correctly.
    Thanks way way in advance.
    MAPS
     
  2. 70Duster440

    70Duster440 Well-Known Member

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    Sticky or crusty float/sender?
     
  3. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

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    Does your temp gauge do the same thing at the same time?
     
  4. MAPS

    MAPS Well-Known Member

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    Gas tank is brand new, the temp guage is disconnected add I have a set of guages on the bottom of the dash that work, (temp,oil, volts)
     
  5. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

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    Reason I ask is the temp gauge and the fuel gauge get their power form the same source (Instrument Voltage Regulator (IVR) on back of dash) and if one was acting odd and the other wasn't it points you in one direction if both are acting the same way points in another.
     
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    • Dana67Dart

      Dana67Dart Most undignified way to get to Colorado!

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      Did it work correctly before the tank swap?
      Did you reattach the ground strap that fits over the fuel hose at the sending unit?
      Did the sending unit look physically good when new tank installed, IE no corrosion etc?
       
    • jdsduster

      jdsduster Well-Known Member

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      tank is new what about sender?hopefully not new also,if so welllll.
       
    • kiss

      kiss Well-Known Member

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      Is your sending unit new (aftermarket) or original?
       
    • GTS Dave

      GTS Dave Where are them dang glasses??! FABO Gold Member

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      Had the same issue, ended up being the ground strap between the tank and fuel line at the tank. the strap uses spring steel connectors, easy to break.
       
    • MAPS

      MAPS Well-Known Member

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      iT WORKED FINE ALL SUMER LONG AT THE END OF THE SUMMER IT STARTED TO MISBEHAVE.
      IM GOING TO GET A NEW IVR AS IVE BEEN TOLD IT MUST BE THAT, MECHANIC WENT OVER EVERYTHING AND SAID IT'S THAT SO I WAS JUST ASKING THE FOLKS HERE TO SEE IF THERE MIGHT BE SOMETHING WE MAY BE MISSING.
      AS USUAL, GRATEFUL TO ALL THE MOPARITES HERE.

      MAPS
       
    • harrisonm

      harrisonm Well-Known Member

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      Since you are not relying on power from the IVR for oil pressure and temp, we cannot see if those gauges are also experiencing malfunctions. If they were, I would lean towards the IVR. I would say that your problem is either the ground strap, the IVR or the sending unit. If you are so lucky as to have the gauge read empty while you are in your driveway some time, crawl under the back of your car and give the gas tank a few good smacks. If it is a bad/sticking sending unit, this may well temporarily jar it back into life. Also, if the gauge is reading empty, try using a jumper wire with alligator clips and grounding out the tank to a known good ground. If the gauge works now, the problem is likely a bad ground strap. If these two tests do not work for you, then I would certainly consider the new IVR route.
       
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      • MAPS

        MAPS Well-Known Member

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        Harrisonm
        I have to admit that's exactly what the mechanic did (clips and grounding) said it should have read or shown something, he said it's the IVR and like I said,I was just asking for a second opinion. I have faith in my mechanic, real faith but like all mopar lovers, we think we just know better about our cars.. lol
        I went to 3 different folks for the six pack I have on the car and they all tried a shytload of things because of the back firing I'd very once in a while, he told me in the end it wad the timing and that's exactly what it was, at times when I opened it up (wide open) it would beck fire and then go he changed the timing, chef third springs in the diaphragm and it ran purr-fectly lol
        Thanks.
         
      • RedFish

        RedFish Well-Known Member

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        Intermittent connection, might be the senders chassis ground path.
        It might be on the positive side too, like the speedy nuts that mount the gauge in and to the printed circuit board.
        You didn't say what model. So I didn't reply.
        The gauges have threaded studs mounted in a piece of fiber board on the back of the gauge. These fiber boards warp with age. Nuts get loose. Thermal gauges have temperature changes, some a lot more than others. So cold makes contact, then heat/movement breaks the contact.
        I wont go into the 3 post fuel gauges also having a ground where they mount in the inst' panel, just ad that these are where the most temperature change is, where the more common loose connections are.
        Good luck with it
         
      • 4spdragtop

        4spdragtop FABO Gold Member FABO Gold Member

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        I can't offer much help here, but be sure to post back what you find Maps. Make sure to disconnect battery if you work under dash.
        I believe the IVR is inside the fuel gauge? I could be wrong.
        We are working on a 69 Barracuda?
         
      • GTS Dave

        GTS Dave Where are them dang glasses??! FABO Gold Member

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        Ditto. This is exactly what I did to find the problem. Just using a test lead (jumperwire w gator clips) from the sender (metal fuel line) to a known good ground, the gauge worked. You could bypass the sender by pulling the wire off of the sender and put a 40 to 50 ohm resistor in line to ground and the fuel gauge should move. If not, then the problem is back towards the wiring or the gauge (or voltage reg IVR )
         
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        • frederick_76

          frederick_76 FABO Gold Member FABO Gold Member

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          Stumbled upon this thread, think I found my problem. Or at least a couple of things to check out!