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  • fuel tank sending unit install, nothing is easy

    Well put in my new sending unit today. Just my luck the gas line to it has a small inside diameter line and wont fit the new unit as it needs a larger diameter hose. I was trying to find a fitting that would fit the hose coming up from bottom car to sending unit and put it into the hose I bought to run to the new unit. Could not find anything. Arrg
    While I had the new unit in I did connect the the wire from gauge to the unit and could get the the gas gauge to read 3/4. It is closer to full, the gas was right at the opening of the sending unit. I bounced the rear around to see if the sending unit just needed a little help. Does it just need some driving around to get it to settle in correctly.
    Tim
    1962 Conv Tbird
    1993 Miata LE
    1994 Miata

  • #2
    The sender and gauge should both be calibrated. It's best to do this with the sender out of the tank. Ground the sender to the body of the car and connect the wire to the sender. Turn the key on. Check the gauge with the sender arm all the way down. The gauge should be at E. Then move the arm all the way up. The gauge should go to F. If the gauge is ok at E but doesn't go all the way to F you can try to bend the tab on the sender so the arm goes up further. If it then goes to F reinsert the sender in the tank and see if it reads closer to full. If it's off both at the E mark and F mark then the gauge probably needs to be calibrated. There are instructions in the TRL.

    John
    John Pizzi - Squarebirds Administrator

    Thunderbird Registry #36223
    jopizz@verizon.net 856-779-9695

    http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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    • #3
      ok i can do that. I still can't think of a work around for my hose connection issue. Will have to find something creative.
      Tim
      1962 Conv Tbird
      1993 Miata LE
      1994 Miata

      Comment


      • #4
        I second John's post. It's always important to know when your tank is empty, so the float needs an unobstructed path to the bottom.

        Understand that your sending unit is a rheostat that ranges from 10-ohms to 100-ohms. This can be measured with an ohm meter (or a multimeter from Harbor Freight for under ten bucks). Driving around will never change the resistances.

        What about the top of the tank? Is this range of motion of the arm consistent with the depth of the tank? That would be determined by the length of the float arm. In other words, if the arm is too long, the float may hit the top of the tank and your gauge will never show 'F'. So, make sure the new float arm is the same length as your original.

        Most arms are too short (on newer cars). You may fill up and run for many miles before the gauge moves at all. This condition is easier to take for your confidence level and most aftermarket arms are intentionally short. Again, the float must be accurate at the bottom of your tank. So how do you attack this?

        I would measure the depth and subtract 1/4" or so. This is your range. Aa John said, it's easier to make all your adjustments with the sending unit on a bench.

        Use a square to make lines across the top and down the side of a long sheet of cardboard. From the top line, mark your depth. Now, use the square to hold the sending unit's mounting base at the top of your line so the sending unit does not tilt.

        The arm needs to nearly touch the bottom but not quite. In other words, there are stops on your sending unit. Don't let the tank stop your float from stopping, let the stop tabs do their job. Bend the arm to make this true.

        If when you raise the float, the float hits the top of your mark before hitting the stop tab, the arm is too long. I use a couple pairs of pliers to bend the arm with a 'Z' in the middle to shorten it.

        If the arm never hits the top line, the arm is too short. How much too short? Hey, a little is ok. You really don't want to hear the float 'clunking' on the top OR the bottom. The float should never touch or rub against anything but liquid.

        I use the 'adjustments' in the back of the gauges to allow the needle to go passed the 'E' when the tank is absolutely empty. This should already be set from the factory. Without a full understanding of the gauge adjustments, don't move them.

        For your hose, use a slightly larger diameter that fits one end and get a good clamp for the smaller end. Those stainless steel gas line (worm-type) work best. - Dave
        Last edited by simplyconnected; September 29th, 2018, 09:36 PM.
        My latest project:
        CLICK HERE to see my custom hydraulic roller 390 FE build.

        "We've got to pause and ask ourselves: How much clean air do we need?"
        --Lee Iacocca

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        • #5
          Originally posted by blue62tbird View Post
          ok i can do that. I still can't think of a work around for my hose connection issue. Will have to find something creative.
          Is it a Spectra sender? The fuel line was changed from 5/16" to 3/8" in 1963. I imagine the sender you bought has the larger 3/8" diameter. You will have to run new 3/8" rubber fuel line to the metal gas line

          John
          Last edited by jopizz; September 29th, 2018, 09:42 PM.
          John Pizzi - Squarebirds Administrator

          Thunderbird Registry #36223
          jopizz@verizon.net 856-779-9695

          http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

          Comment


          • #6
            yea it is a 3/8 connector.
            Tim
            1962 Conv Tbird
            1993 Miata LE
            1994 Miata

            Comment


            • #7
              Originally posted by jopizz View Post
              Is it a Spectra sender? The fuel line was changed from 5/16" to 3/8" in 1963. I imagine the sender you bought has the larger 3/8" diameter. You will have to run new 3/8" rubber fuel line to the metal gas line

              John
              I don't think it is spectra. I compared the units and the arm lengths were the same, travel of the arm seemed to be the same but I did not look that closely at it, i will when I pop it back open. I will get back to it when I can run the 3/8 gas line. Won't I run into the same issue with the 3/8 being too big for the metal line it will connect to under the car?
              Tim
              1962 Conv Tbird
              1993 Miata LE
              1994 Miata

              Comment


              • #8
                Originally posted by blue62tbird View Post
                Won't I run into the same issue with the 3/8 being too big for the metal line it will connect to under the car?
                You shouldn't have any problem clamping the slightly larger rubber line. It's not under any pressure so I don't think it will leak. A sender with a 5/16" outlet is not being reproduced so you have no choice but to make it work. Your other option is to try and find a 5/16" to 3/8" hose adapter. Try NAPA, they usually have a decent assortment of adapters.

                John
                John Pizzi - Squarebirds Administrator

                Thunderbird Registry #36223
                jopizz@verizon.net 856-779-9695

                http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

                Comment


                • #9
                  Well I finally got around to getting the fuel line issue resolved. I know the tank is full based how close the fuel was to the opening for the sending unit.
                  The gauge is reading close to half. I drove around last night, maybe 15 miles, then will to work and back today for another 20 miles. The gauge seems to be moving down fast than I thought even with it reading wrong. Got to wonder if the unit is bad. The float assembly hung exactly as the old one did, assuming when it worked it read correctly. So with a little more driving my thought was IF the float it hitting the top of the tank it is keeping it from reading full and that once I burned off a little gas it may eventually go up to 3/4 then drop.
                  If no to all above I can replace it or do the other things described above.
                  Tim
                  1962 Conv Tbird
                  1993 Miata LE
                  1994 Miata

                  Comment


                  • #10
                    I finally got to drive the bird today and filled the tank and the fuel gauge went to full. It was a little over quarter when I filled it which only took about 9 gallons. I take these gauges are just not real accurate or does that last quarter drop slow? If I recall the take is like 25 gallons?
                    Tim
                    1962 Conv Tbird
                    1993 Miata LE
                    1994 Miata

                    Comment


                    • #11
                      Originally posted by blue62tbird View Post
                      If I recall the take is like 25 gallons?
                      It's a 20 gallon tank.

                      John
                      John Pizzi - Squarebirds Administrator

                      Thunderbird Registry #36223
                      jopizz@verizon.net 856-779-9695

                      http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

                      Comment


                      • #12
                        If your electrical components are working correctly, your gauges are VERY accurate.

                        The most important setting is at the bottom of your tank. You need to know when you're out of gas. The way your sending unit works is, when the float is all the way down, the electrical resistance is at its greatest. The bottomed-out float should make the sending unit read 100-ohms on an ohmmeter. That means very little current passes through the gauge and it should show, 'E'. The gauge should indicate the same when you remove your key.

                        What resistance value did you get before filling the tank? Tim, I wrote about this eight posts ago so I would expect you measured your sending unit. - Dave
                        My latest project:
                        CLICK HERE to see my custom hydraulic roller 390 FE build.

                        "We've got to pause and ask ourselves: How much clean air do we need?"
                        --Lee Iacocca

                        Comment

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