fuel tank sending

Discussion in 'Electrical and Ignition' started by Snake, Apr 13, 2012.

  1. Snake

    Snake Mopar Nut

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    Ok had this problem when first started to restore the Dart.My fuel Gague reads way empty now the sending unit is only 3 years young.could someone refresh me on how to test to find the problem.If I remember right if I pull the wire off the unit and ground it the gauge should go to full meaning the gauge is good and the sending unit is bad right? I do have a ground wire back there.So if I ground that wire and nothing happens were do I look next thankssssssssss fabo.
     
  2. racerhog

    racerhog RacerHog likes his Mopars

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    Yep.....

    If all is good to that point....Pull the sender and bench test it....
     
  3. mcnoople

    mcnoople Well-Known Member

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    Basically the procedure would be

    1. check voltage going into gauge
    2. check continuity of sender wire from gauge to tank
    3. verify grounding of tank/sender
    4. substitute the fuel sender with a resistor of known value to simulate the tank sender.

    If all of the above check out then I would pull cluster and gauge

    this thread is from a week ago and has the resistance values for the tank sender
    http://www.forabodiesonly.com/mopar/showthread.php?t=184924
     
  4. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    Ground the sender wire to the frame without the key on, turn the key on and see if the gauge goes to full, if so the gauge should be good. When you do this do it quickly as you can damage the gauge if left on too long.

    Do you have the ground strap from the sender to the fuel line?
     
  5. wjajr

    wjajr Well-Known Member

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    Make sure there is a good ground to the sending unit. Factory uses a metal strap which clipped to the male fuel fitting on sending unit bridging the rubber coupler and the other end clipped to fuel line.

    Sometimes that strap becomes lose, rusts apart, or fuel line loses its ability to provide a competent grounding point. This lack of ground at sending unit is the cause of gage not working more often than not.

    You can order a new strap, or make up a jumper wire using a few small hose clamps to attach to steel lines accomplishing the task of grounding sending unit.

    Another test you can do is to check the resistance of the sending unit. It should be anywhere between 10 and 75 ohms give or take depending on level of fuel in tank. Just touch one VOM probe onto electrical stud at sending unit, and the other to its fuel tube.
     
  6. Snake

    Snake Mopar Nut

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    Ya i do that was the first thing i did back than.
     
  7. 67Dart273

    67Dart273 Well-Known Member

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    These are a simple series circuit

    The voltage limiter is supplied by the "ignition run" line which powers the cluster and warning lights (oil light)

    The output of the limiter goes to both fuel and temp gauges, so if the temp gauge seems OK, the limiter is at least functioning

    From the sender terminal of the fuel gauge, the sender wire goes down to the left kick panel, to the connector at the rear harness under the sill plate and to the rear, to the tank.

    So if grounding the seder wire does nothing, try grounding the correct wire in the kick panel at the connector, and if nothing, time to pull the cluster.
     
  8. Snake

    Snake Mopar Nut

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    Ok will try that so what do I do if I have to pull the cluster whats next new gauge?
     
  9. 67Dart273

    67Dart273 Well-Known Member

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    There are several issues that crop up in these clusters

    First, make sure your switched ignition (dark blue) or "ignition run" power to the cluster is solid

    Second, make sure your sender wire and sender are not the problem

    Then....

    1 The cluster harness connector can be loose/ corroded

    The PC board connector pins can be loose/ broken corroded

    So solder the pins if possible, in my case SEVERAL of the pins were broken/ loose, corroded, bad shape. So I elected to go with a pair of "Molex" style connectors which I bought at RadShak. I just soldered leads to the board traces and brought them out to the Molex connectors. If you search the site, there are several posts about guys fixing these connectors

    2 The PC board / cluster can have a poor ground

    Loosen/ tighten all board mount screws, clean the board if necessary, and either solder a wire to the board ground, or attach a lead wire to a board ground screw. Bring this out and screw to the column support

    3 The VR can be faulty, even though it is somewhat functional, may not be the correct output

    The VR SOCKET in the PC board may not be making good contact with the board

    Replace the VR, and check resistance and examine the brass fingers that make the contacts. On my 67, I soldered short wires from the brass clips to the board traces. They were NOT making contact on mine

    4 The gauge nuts ("fake" sheet metal) may be loose/ corroded, as can be the PC board surface

    Replace the nuts with real nuts, clean the board if necessary, and don't overtighten them.

    5 And of course the gauge can be faulty

    After you've checked and fixed everything else, this is a possibility. Both fuel and temp use the same sender resistance, this is where the test resistances come into play. You can either get resistors from (limited selection) at Radio Shack, or places like Mouser Electronics or Digikey

    the resistance to obtain MT, 1/2, and full (or "hot") are

    L = 73.7 Ohms (empty)
    M = 23.0 Ohms (1/2)
    H = 10.2 Ohms (full)

    Another way, if you have your fuel sender out, is to lay it out, move it until you get the resistance listed above, and then hook to the sender end of the gauge with test leads.

    The gauge needs a properly working VR, or you can rig a supply (battery) of 5--5 1/2V
    You can buy battery holders from RadShack, and if you can rob some AA cells out of some of your remotes, etc, and they are "down" just a little from new, they should be very close

    And, for example, if you think the temp gauge is OK, you can compare readings between the two gauges. With the same voltage to the gauges, and the same sender resistances, they should read very close to the same. That should give you and idea if one is way off from the other.
     
  10. Snake

    Snake Mopar Nut

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    Thankssssssssss 67Dart273 for sticking with me,I did find the problem,not enough gas in the tank:eek:ops: Back some 3 years ago when I got the new sending unit I ask for help here because the gauge would not move until there was 1/4 of gas in it.The needle was so far down I thought the sender was toast again.There is something wrong tho with the sending unit so if the needle says 1/4 there is like 1/2 in the tank.I found this out by testing the sender out of the tank and moving it by hand than seeing what the gauge said.again big thanks,my bad.:violent1:
     
  11. DusTed74

    DusTed74 Well-Known Member

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    I'm having the same issues right now on my Dart. I'm reading only 2,5 volts on the blue wire that goes to the sending unit. Is this a correct voltage reading or is it really low?

    Thanks in advance..........Ted
     
  12. 67Dart273

    67Dart273 Well-Known Member

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    Hi DusTed. You really should start a separate thread. There are no specs for what you read on the sender side of the gauge, and the original VR "pulsed" just like a flasher, so there was no real spec for voltage TO the gauge, either.
     
  13. racerhog

    racerhog RacerHog likes his Mopars

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    Had a feeling thats what you where going to find....:coffee2:
     
  14. DusTed74

    DusTed74 Well-Known Member

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    This was really strange. It turned out to be a blown fuse. I was getting low voltage right to the main power feed to the dash gauges. I followed that down to the fuse box and found the fuse had 12 volts on the feed side and only 5 on the other side. I've never seen anything like that before. Everything works just fine now.
    Thanks..........Ted
     
  15. 67Dart273

    67Dart273 Well-Known Member

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    Actually, "that can't be." The gauge power is NOT fused, it comes directly off the igntion switch to the cluster. This is the same ignition "run" (IGN1) that powers the alternator field, regulator, and ignition. It powers the voltage limiter for the gauges, and the oil warning light, as well as the brake warning light.
     
  16. Snake

    Snake Mopar Nut

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    I here ya there when doing my tasting I was worried about frying my ballets resistor and such.you sure know your stuff 67dart273
     
  17. Snake

    Snake Mopar Nut

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    Yup pecker head for sure,I am lol.
     
  18. RedFish

    RedFish Well-Known Member

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    Agreed. A fuse wasn't that actual culprit.
    Lets imagine the dark blue with white has a fault/weak connection somewhere like a welded splice. Everywhere the branches go could show low or no voltage.
    Owner states he followed that wire to the fusebox so he likely disturbed the weak link and temporarily corrected the problem. My best guess