How to test unknown fuel gauge.

Discussion in 'Electrical and Ignition' started by Futzy1, Apr 16, 2018.

  1. Futzy1

    Futzy1 Well-Known Member

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    First off, I'm sorry. I'm sure if I did a little more research I could find the answer, but I have to go to work and I'm super impatient.

    With that aside, I have been driving my 1973 dart custom for almost 2 years now. My last older vehicle had a bad fuel gauge the never quite made it to full or back down to empty, and unfortunately I didn't find this out until I was sitting on the side of the road on a 110° day. As a result I've just played it safe, and never let my dart dip below a quarter tank.

    I've done all the important drive stuff and I'm now working on the smaller things and I'm wondering if there is a way to confirm my fuel gauge operation that doesn't involve waiting for it to sputter out on me.

    Thanks as always

    Ps when I fill her up the gauge does make it to "f"
     
  2. 67Dart273

    67Dart273 Well-Known Member

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    Only way I know (this IS installed / working in a car right?) is to carry a gallon of "spare" in a safe manner, drain as much as you can (siphon, disconnect pump, drain into can) until you get the gauge "down" and then drive it till it drops. Heck you can just drive it round and round and round and rou........the block as long as the neighbors don't get upset LOL
     
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    • Futzy1

      Futzy1 Well-Known Member

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      Yeah that's what I've been learning towards. The only other option I can think of would be to disconnect the sender and test the resistance against factory specs. Honestly I'm not sure which would be more of a hassle
       
    • 67Dart273

      67Dart273 Well-Known Member

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      Factory specs don't tell you much because the float/ arm may be bent some from "factory." They were not necessarily "that accurate" but "you hope" you can run it down to E and keep going awhile LOL

      There's a device.......about 50 bucks.........called a "meter match" can calibrate the thing against some variation. Don't know how far they will compensate

      TechnoVersions - MeterMatch for Analog Gauge Correction
       
    • 67Dart273

      67Dart273 Well-Known Member

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      I've written "a bunch" here (hop most of it is correct LOL) about the problems with these gauges and accuracy. It's not just the senders, sometimes it's also connections in the cluster, wiring, the accuracy of the instrument regulator, etc etc. Here are the factory resistances:

      c-3826-jpg-jpg.jpg
       
    • AJ/FormS

      AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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      Yeah I ditched that factory point-type power interrupter general averager, years ago. There was a magazine article that came out in 99 or 2000 or close to that, where a guy built one from a 5v computer part and a resistor IIRC. Well I couldn't get one in my dash fast enough. That solved the drifting inaccurate needle. I think that was an E-burg story; possibly as late as 2003.Probably Mopar Action: I was big into that rag.
      Then I dropped the tank and bent the pick-up sock to sit on the bottom.
      And finally figured out where the sender had to be to show E on the gauge. Then I poured one gallon of gas in the tank and bent the float arm to indicate E on that amount of gas. Badaboom, now I have exactly 1 gallon in there when it says E. And the new electronic-regulator holds the needle dead-nuts accurate.

      OK that sounds too easy. Yeah it took several tries to get the float to the right height,lol.
       
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      • Murray

        Murray FABO Gold Member FABO Gold Member

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        Grounding the sender wire should let you know if the gauge is capable of showing "full" or "empty". This will help in determining if your problem is the gauge or sender.
         
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        • Futzy1

          Futzy1 Well-Known Member

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          I'm gonna laugh when I check all this stuff, and it turns out I'm just being overly cautious, and it was all completely functioning until I got my grubby hands on it.
           
        • TrailBeast

          TrailBeast Slightly Twisted Member

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          I built one of those for my car when I had the factory gauge and sender and they work just fine.
          IIRC it cost me about 85 cents at Radio shack.
          I stopped using it when I switched to an Ohm matched set sender and gauge.

          guageregulator.jpg
           
        • Futzy1

          Futzy1 Well-Known Member

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          :rofl::rofl::rofl::rofl: 20180417_093611.jpg
           
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          • TrailBeast

            TrailBeast Slightly Twisted Member

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            I realize that, but the part still exists, and you wouldn't be asking for a fuel gauge voltage limiter anyway.
             
          • Futzy1

            Futzy1 Well-Known Member

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            Sorry, that was not a critique on you, just my reaction to the RadioShack's failed business model.

            I hate that there is no "subtext keyboard" for the internet. Lol
             
          • AJ/FormS

            AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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            Yeah that's the one; some assembly required
             
          • krazykuda

            krazykuda FABO Gold Member FABO Gold Member

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            Del, weren't you going to try to make testers for the gauges??/ We cracked the code a couple of years back for the resistors...

            @halifaxhops was also going to try to copy one and I have one of his prototype gauge testers that are battery powered...

            Those can be used to test the gauge sweep...
             
          • Futzy1

            Futzy1 Well-Known Member

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            Not to butt in where I dont belong, but I'm much more proficient at electronics than automotive, and I'd love to offer a hand anywhere I can.
             
          • halifaxhops

            halifaxhops It's going to get stupid around here! FABO Gold Member

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            Pretty easy just three resistors and a rotary switch just went a bit further and made mine so It can test the gauges out of the car.
             
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            • 67Dart273

              67Dart273 Well-Known Member

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              Going to work part time ate up a lot of time LOL. Yes, really, you can get by with the three resistors, you don't even really need a switch, you can just "alligator clip" them. I've forgotten what wattage they should be as they do draw some current. 1 watt would probably be safe enough for the short time you are testing
               
            • Murray

              Murray FABO Gold Member FABO Gold Member

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              This would be great to develop a simple tester for the three gauges, gas, oil and water. If the basic parts could be identified, we could build it ourselves. I had a similar tester made by AC many years ago that got destroyed in a shop fire. Have been missing that tester ever since.
               
            • krazykuda

              krazykuda FABO Gold Member FABO Gold Member

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              Being able to test gauges out of the car is a handy option... :thumbsup:
               
            • Murray

              Murray FABO Gold Member FABO Gold Member

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              I understand how to test the three senders, gas, oil, temp. Being able to test the accuracy of the gauge out of the car would be great. I'll start- the source voltage would have to be 4 volts. The sender side of the gauge would need three options- 74 ohms, 23 ohms and 10 ohms. To adjust accuracy you bend the needle. How am I doing so far?