Possible sender fault

Discussion in 'Fuel and Air Systems' started by TOY440, Apr 17, 2018.

  1. TOY440

    TOY440 Member

    Messages:
    12
    Likes Received:
    0
    Joined:
    Jan 15, 2013
    Location:
    Sydney
    Local Time:
    11:56 AM
    ok guys, was jacking car up from the diff, slipped off the jack and came down on the jack on the fuel tank. Didn't really damage the tank at all, just a bit of a dint as the jack is a decent size.

    I noticed my fuel tank now reads full. I disconnect the feed wire from the sender (I only have one wire, some have 2 wires, like an earth, mine has one), and it still reads full, I earth out the wire, it reads empty but very very slowly creeps towards full.

    Any ideas what my issue could be?

    Thanks in advance.
     
  2. Steven190

    Steven190 FABO Gold Member FABO Gold Member

    Messages:
    462
    Likes Received:
    142
    Joined:
    Jan 13, 2012
    Location:
    Omaha
    Local Time:
    8:56 PM
    I think that the tank has a ground wire, or strap, the grounds the tank. Most time it is connected on the fuel tube on the sending unit, to go around the rubber piece.
     
  3. TOY440

    TOY440 Member

    Messages:
    12
    Likes Received:
    0
    Joined:
    Jan 15, 2013
    Location:
    Sydney
    Local Time:
    11:56 AM

    Yeah, some do, some don't, mine doesn't. I'm not too concerned about the earth, I'm concerned why my gauge is reading full all the time now, perhaps I damaged something inside, resistor perhaps......
     
  4. 65wgn440

    65wgn440 Well-Known Member

    Messages:
    194
    Likes Received:
    50
    Joined:
    Aug 16, 2016
    Location:
    Toledo, ohio
    Local Time:
    9:56 PM
    Possibly bent/ damaged float arm. Have to pull it and check.
     
  5. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

    Messages:
    644
    Likes Received:
    173
    Joined:
    Jul 16, 2017
    Location:
    Northern Colorado
    Local Time:
    7:56 PM
    If I'm not mistaken the gauge reads full when the resistance to the gauge is low like 10 ohms and empty when the resistance is in the 72 ohm or above range. If you short the sender wire to ground the gauge should read full. If it is not connected or shorted it should read empty. If it is reading full when disconnected and not grounded I suspect you pinched the wire and it is grounded. Grounding the wire and you get empty but slowly raises to full might be you moved the wire away from the sort and when you let the wire be it moves back to the short.

    Also it is important to be sure the tank is properly grounded or there is no path for the ground side of the sender to get back to the chassis and make a complete circuit.
     
    • Agree Agree x 1
    • 67Dart273

      67Dart273 Well-Known Member

      Messages:
      36,131
      Likes Received:
      4133
      Joined:
      Oct 14, 2010
      Location:
      Idaho
      View My Photos
      Local Time:
      6:56 PM
      Sorry this does not make sense. Dana67 ^^ above is correct. When the sender is "full" the resistance is low, causing more current to flow in the gauge. Here are the factory tester values

      c-3826-jpg.jpg

      I would re-test.......perhaps you did not get the sender wire well connected to ground.
       
      • Agree Agree x 1
      • Dana67Dart

        Dana67Dart Most undignified way to get to Colorado!

        Messages:
        644
        Likes Received:
        173
        Joined:
        Jul 16, 2017
        Location:
        Northern Colorado
        Local Time:
        7:56 PM
        I remembered 72 when the value is 74. Not too bad from memory from an old fart like me... now where did I put my glasses!
         
      • 67Dart273

        67Dart273 Well-Known Member

        Messages:
        36,131
        Likes Received:
        4133
        Joined:
        Oct 14, 2010
        Location:
        Idaho
        View My Photos
        Local Time:
        6:56 PM
        That value varies depending "where you read." Bear in mind that value did not come from any Chrysler literature that I'm aware of. It came from guys measuring the dealer tester!!! And they likely vary as well!!
         
      • Frnknsteen

        Frnknsteen FABO Gold Member FABO Gold Member

        Messages:
        261
        Likes Received:
        118
        Joined:
        May 26, 2011
        Location:
        Spencer, IN
        Local Time:
        9:56 PM
        I agree with you Dart. I have seen references ranging from 73ohms to 75 ohms in different readings. I don't think it makes a huge difference in those two numbers.

        To test my gauges, I set my power supply to 5volts and verified. My meter read 4.99 volts. I connected two 150 ohm resisters in parallel to make my hi resistance wire. When I test resistance in the test wire after assembling them, I get 74.8 ohms. When I test my gauges with that resister, I barely see the gauge move. I then put in the 23 (22.9 actual) ohm resister wire and the gauge goes to about midpoint. The 10ohm (9.8ohm actual) brings it to just over the max mark.
         
      • Dana67Dart

        Dana67Dart Most undignified way to get to Colorado!

        Messages:
        644
        Likes Received:
        173
        Joined:
        Jul 16, 2017
        Location:
        Northern Colorado
        Local Time:
        7:56 PM
        Toy440 any update??
         
      • harrisonm

        harrisonm Well-Known Member

        Messages:
        1,602
        Likes Received:
        855
        Joined:
        Jan 16, 2005
        Location:
        Topeka, KS
        Local Time:
        2:56 AM
        The original post said that the car slipped off the jack and the jack hit the tank. Couldn't the wire going to the sending unit have gotten pinched between the tank and a frame rail? That would ground out that wire and cause the gauge to read full all the time when the key is on.
         
        • Agree Agree x 1
        • TOY440

          TOY440 Member

          Messages:
          12
          Likes Received:
          0
          Joined:
          Jan 15, 2013
          Location:
          Sydney
          Local Time:
          11:56 AM
          Ok guys, got it sorted. Due to an aftermarket electric fuel pump being fitted, the lines were changed also. There seemed to be an alloy vent tube that may/may not have been used as some type of earth. I have made an earth wire and everything seems to be working fine now.

          Thanks for all the advice