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    Wonky Digital Fuel Gauge

    My friend's '96 CV has a digital dash. The fuel gauge either reads "CO" (circuit open) or "F". Nothing anymore in between. I don't think the issue is in the dash but rather a wiring short from the sender to the dash (and most likely near the fuel tank). Could be the sender itself but if I had to bet, I'd say a short. Thoughts?
    What I Own: 1993 Mercury Grand Marquis GS
    What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

    #2
    Most likely the level sender in the tank. If a multimeter is handy, get under the car and pull the wiring connector off the fuel pump assembly and check the resistance of the level sender. Not sure which two wires that is, but if the harness has two fat wires and two skinny wires, go for where the two skinny ones connect. That will be the level sender. If you get more than 200 ohms, the sender is bad or the connections are crap. The range should be less than 200. Somewhere between 20 and 160 from what I can find. If you get a reading near the range, try cleaning the connector with some contact cleaner. Otherwise, probably going to have to replace the assembly. While you're under there, you can check the wires for damage.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Originally posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Originally posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

    Comment


      #3
      If you are getting a "circuit open" message, than it wouldn't be a short, but would be an open circuit?
      I would test for continuity and look for a broken/loose wire
      ..

      Comment


        #4
        Broken or loose wire is a real possibility. A lack of continuity (broken connection) would be a form of short? I was told, the tank had been changed along with a new Motorcraft Fuel Pump/Sender some years ago so who knows how the mechanic went about his business?
        What I Own: 1993 Mercury Grand Marquis GS
        What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

        Comment


          #5
          A short would likely blow a fuse, from 12v making contact to ground before reaching the load. A "shortened" circuit.
          An open just means that 12v is being sent but never reaches the load (loss of continuity). An "open" or not closed (incomplete) circuit.

          ..

          Comment


            #6
            Thanks for the detailed explanation and most helpful video! I would agree the issue is in the wiring as opposed to a problem in the digital dash (more expensive but easier to get to - at least for me!).
            What I Own: 1993 Mercury Grand Marquis GS
            What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

            Comment


              #7
              The usual culprit is a crusty connection at the fuel tank connector, which is why I said to check that first. It's also fairly easy to get to (other than the crawling under the car part).

              Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
              rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
              Originally posted by gadget73
              ... and it should all work like magic and unicorns and stuff.
              Originally posted by dmccaig
              Overhead, some poor bastards are flying in airplanes.

              Comment


                #8
                Originally posted by sly View Post
                The usual culprit is a crusty connection at the fuel tank connector, which is why I said to check that first. It's also fairly easy to get to (other than the crawling under the car part).
                I'll try to get to it to check out as that may somewhat "easy" to get to and hopefully repair. So many projects, so little time!! Haven't been under the back end of it in some time - anybody know if the connector is on the top or side of tank. I'm thinking side but don't remember.
                What I Own: 1993 Mercury Grand Marquis GS
                What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

                Comment


                  #9
                  I'm going with bum sender. Its a wiper on a resistance track that is printed on a circuit board. Fair bet the board is cracked and unless the float is full up its hitting the dead part of the board.


                  the sending unit is on the front side of the tank directly above the diff cover.
                  86 Lincoln Town Car (Galactica).
                  5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                  91 Lincoln Mark VII LSC grandpa spec white and cranberry

                  1984 Lincoln Continental TurboDiesel - rolls coal

                  Originally posted by phayzer5
                  I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                  Comment


                    #10
                    Originally posted by gadget73 View Post
                    I'm going with bum sender. Its a wiper on a resistance track that is printed on a circuit board. Fair bet the board is cracked and unless the float is full up its hitting the dead part of the board.


                    the sending unit is on the front side of the tank directly above the diff cover.
                    Argh! I assume the connection is there as well?
                    What I Own: 1993 Mercury Grand Marquis GS
                    What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

                    Comment


                      #11
                      Originally posted by friskyfrankie View Post
                      Argh! I assume the connection is there as well?
                      If it's the same as a 93, yes there is a 4-prong plug that plugs onto the sending unit.

                      Click image for larger version

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                      ..

                      Comment


                        #12
                        Originally posted by massacre View Post
                        If it's the same as a 93, yes there is a 4-prong plug that plugs onto the sending unit.

                        [ATTACH=CONFIG]57439[/ATTACH]
                        Thanks! Nice to know what it looks like before seeing it in person.
                        What I Own: 1993 Mercury Grand Marquis GS
                        What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

                        Comment


                          #13
                          According to Rockauto, it looks like this (Dorman) - now I may be confused?

                          Click image for larger version

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                          What I Own: 1993 Mercury Grand Marquis GS
                          What I Help Maintain: 1996 CV / 1988 CV / 1988 Tempo

                          Comment


                            #14
                            No it is probably what rockauto said. I was going by a different model year.
                            ..

                            Comment


                              #15
                              It's a 4-pin connector either way. Also, keep in mind the fat vs skinny wires to figure out which ones to test.

                              I'm leaning towards bum sender myself. I have a spare one from my old fuel pump assembly for my 93 just in case the "new" sender dies. I had to replace mine due to the pump giving up. Just make sure to run the tank down to about a quarter tank and then changing that pump/sender assembly is about a 30 minute job. Hour if it's stubborn.

                              Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                              rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                              Originally posted by gadget73
                              ... and it should all work like magic and unicorns and stuff.
                              Originally posted by dmccaig
                              Overhead, some poor bastards are flying in airplanes.

                              Comment

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