Fuel Fuel Sending Unit Problem

Discussion in 'Classic Mustang Specific Tech' started by biggyfan1, Jun 22, 2013.


  1. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    Ok guys the fuel gauge in my 67 only went up to the empty spot when I start the car or put my key to the aux position. so I went out and bought a new sending unit and installed it and still it doesn't work. now here is the weird part. if I take the sending unit out of the tank and push the base of the unit to a solid ground the gauge works and then as soon as I install it, it doesn't work. is this thing supposed to be grounded?
     
    #1
  2. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    I also tested the gauge and grounded the sending unit wire and it pegged to full when it was grounded.
     
    #2
  3. iskwezm

    iskwezm Advanced Member

    Joined:
    May 24, 2005
    Messages:
    4,146
    Likes Received:
    17
    Trophy Points:
    69
    Location:
    Rowland Heights,California
    this would indicate from the wire forward(to the gauge) is good. The sender is grounded through the tank mounting screws.
     
    #3
  4. horse sence

    horse sence Please don't call me Mom SN Certified Technician

    Joined:
    Nov 30, 1999
    Messages:
    4,124
    Showcase:
    164
    Albums:
    5
    Likes Received:
    685
    Trophy Points:
    163
    Location:
    Wile Coyote's stunt double
    try a ground wire at the tank to the body.if that works i would check the screws at the tank and see if they are loose.if tightening the screws doesn't work i would put a ground strap on it
     
    #4
  5. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    ok so I removed the tank and then I wire wheeled the rim around where the gas tank seats to the body of the car. I also wire wheeled the holes where the bolts go threw the tank. got it all bolted in and tight and NOTHING. take it out, touch it to the exhaust and it works. I made sure the ring that secures the sending unit was nice and tight as well. took a ground wire from a bolt on the tank and the other end to an area where other wires are grounded and still nothing. im at loss for words and had to put the hammer out of reach because I might use it on a window. I am also adding 7 gallons of fuel to the tank so I know that should be enough for a reading, right?
     
    #5
  6. j69302

    j69302 Active Member

    Joined:
    Jan 31, 2006
    Messages:
    325
    Likes Received:
    1
    Trophy Points:
    29
    Make sure the float on the new sending unit is good. I bought a sending unit, came with a plastic float, was bad. It would register some indication but not correct. My friend had a spare brass float... I soldered it onto the unit and fixed that.

    However, all the trouble shooting you have done so far only tests the wire going to the sending unit and not the unit itself. You need to functionally check the unit off the car.

    Take the sending unit out. disconnect the wire, with a multimeter check for resistance from the wire connection on the unit , to the metal ring of the send unit where it contacts the tank.

    Also, check for a good ground on the tank itself where the unit installs, to a chassis ground. If the tank is properly grounded, the fault is in the unit itself.
     
    #6
  7. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    ok so I bench tested the old sending unit that I thought was the problem and it had a ohm range of 10.2 to 77.6 so this unit is still good. then what I did is test the new unit while it is still installed in the tank and it reads 59.8 with about 7 gallons of gas in the tank. no matter what position the key is in the needle reads \E. Guys im thinking that maybe 7 gallons is not enough for a reading.....? We have determined that the wire and gauge are good so im still stumped.
     
    #7
  8. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    im about to drain the tank again and bench test this new unit and see if it has the proper range that it needs then I will triple check the ground between the tank and chassis. if none of that works then turn on your local news as you watch a red 67 mustang ghost drive down the freeway with a brick on the gas pedal.
     
    #8
  9. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    ok so both units have now been checked and both work on the bench with an ohm meter. Im going to wire brush the ring and then scrub the gas tank opening with a plastic brush to remove 100% of all dirt even though I know its 99% clean already. The sending units both work when you have them out of the tank and grounding anywhere on the outer tank. as soon as I touch the unit to the tank the needle will show the correct range pre float position. somehow they are not getting grounded when installed.
     
    #9
  10. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    Ok guys its fixed. after slapping my self over 30 times in the face I just added 8 more gallons of gas to the tank and now it wants to show a reading. so I guess 6-7 gallons means im on dead dead \E. now with 14 gallons in the take it reads 1/2 full. this thing must have a 28 gallon take if 14 is 1/2. I do notice that my tank has a dent on it but its not that bad. and with a dent it should read fuller not emptier.
     
    #10
  11. horse sence

    horse sence Please don't call me Mom SN Certified Technician

    Joined:
    Nov 30, 1999
    Messages:
    4,124
    Showcase:
    164
    Albums:
    5
    Likes Received:
    685
    Trophy Points:
    163
    Location:
    Wile Coyote's stunt double
    then what you need to do is bend the rod untill it reads empty at epmty
    .i always set mine to read empty with a gallon still in the tank.
     
    #11
  12. biggyfan1

    biggyfan1 Member

    Joined:
    Mar 10, 2006
    Messages:
    187
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    High Desert CA
    pulling the unit again might have to wait till i burn all this gas out :) but i thank each of you for your advice.
     
    #12

Share This Page