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Technical 1952 3100 Fuel Gauge Always Reads "E"

Discussion in 'The Hokey Ass Message Board' started by Ty C. Denton, Jul 10, 2019.

  1. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    I hope I'm posting this in the right section. I read through all the guidelines and I think this is the right place.

    I just reacquired my grandfather's '52 3100 from my aunt and uncle who had it fully restored. My fuel gauge always reads E, however. I've done some searching on this forum and some Googling and am still having issues.
    • The first thing I did was pull the sending unit and bench test it.
    • I get 0-30 ohms for E/F on the bench (within 1 or 2 ohms each way).
    • Key on, sender wire disconnected from sender, gauge goes to F
    • Reattach sender wire to sender, key on, gauge stays at E and I get something around 118 ohms resistance from sending wire post on the sender; key off and this drops to about 1.5 ohms
    There was a 12-volt conversion done during the restoration, but I'm not sure if the gauge was changed out to a 12-volt gauge. The gauges that are installed are clearly aftermarket (same style, font as originals, but white face with black lettering/numbering). I checked the back of the gauge and did not see a runtz resistor installed; just a red wire on the E side of the gauge and black wire on the F side. I feel like either one of two things could be the issue after testing: either it's a 6V gauge and I need the runtz OR the sending wire is grounding out somewhere between the tank and the gauge. Any insight would be very much appreciated. Thanks!!
     
  2. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    I tried one more thing. I disconnected the sending wire from the sending unit and then ran a jumper between the sending unit and the gauge and it still reads E.
     
  3. 52HardTop
    Joined: Jun 21, 2007
    Posts: 1,078

    52HardTop
    Member

    Usually a Runtz resister would have been installed on the power side of the gauge when the 6 volt instrument is to be used after a 12 volt swap. The sending unit is just a resister si the 12 volts shouldn't cause it any harm. If the gauges are new, you would think the gas gauge was 12 volt. Maybe not and it was burned up when the higher voltage was introduced.
     
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  4. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    Thanks, 52HardTop. My aunt and uncle are out of town at the moment, but I'm going to get with them and see if they can put me in touch with whoever did the restoration. Hopefully that person will know more about the gauges.
     

  5. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    I finally got a Runtz installed on my fuel gauge, but it still doesn't work. In still waiting to find out if the gauge was switched out for a 12v gauge when the conversion was done, but figured I'd try the Runtz in the meantime. Before installing the Runtz, when I turned the key on, the gauge would move ever so slightly lower past E. With the Runtz installed, I get no movement at all. I get 14v and some change on the battery side of the Runtz and 9v and some change where the Runtz connects to the gauge. I tried making a ground jumper from sender to ground and also a jumper from the sender side of the gauge to the sender post on the sender and still nothing. If I disconnect the sender wire from the sender, gauge goes to F with the key on. Also with the key on, I get about 1.7v at the sending unit. Does this sound like the gauge is bad?
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    It sounds like the guage is working properly. The sender is shorted to ground, or the float is full of gas, or the truck is out of gas, or something.

    If you have an Ohm meter (like on a digital multimeter) you can measure the resistance of the sender to ground, after you disconnect the sender wire. It should read anywhere from zero to 30 ohm, depending on how full the tank is. If you remove the sender so you can manually move the float up and down, it should read 0 ohms at the lowest point of float travel, and 30 ohms at the highest, and a proportional number in the middle.
     
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  7. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    Thanks, squirrel. I did bench test the sender and it seemed to be working properly. I did not, however, disconnect the sender wire and test resistance with the sender installed in the tank. I will give that a shot and report back. Thank you!!
     
  8. Do you have power and ground connected to the gauge?

    The actual gauge should only have a wire from the sender and another wire to ground.
    ( if the gauge is lit then a power and ground to the bulb as well)

    I’m thinking your gauge is not wired correctly or it’s the wrong gauge or sender.

    Some fuel gauges go low to high resistance and some high to low
    Also some to 30 ohmsand some to 60.

    Need to know first if your gauge and sender are compatible
    And second if it’s wired correctly
     
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  9. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    I'm assuming it's the factory gage and sender, or a direct replacement.
     
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  10. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    @VANDENPLAS The gauge is wired as such: 12v switched ignition to "E" side of gauge (via the Runtz), sender wire to "F" side of gauge. The sending unit has the sender wire from the "F" side of gauge hooked up to the post protruding from the top of the unit and then the sending unit itself is grounded via a wire from one of the hold down screws to a ground location on the back of the cab. I've jumpered the ground wire from the sending unit to a known good ground with no change and also jumpered the sending unit wire from gauge to sender with no change. I've also bench tested the sender and it appears to be working. The only thing I have not done is remove the sender wire from the sending unit and test the resistance while installed in the tank as @squirrel mentioned.
     
  11. farmalldan
    Joined: Sep 4, 2009
    Posts: 141

    farmalldan
    Member
    from Duncan, OK

    "Before installing the Runtz, when I turned the key on, the gauge would move ever so slightly lower past E. With the Runtz installed, I get no movement at all.[/QUOTE]
    This makes me think gauge polarity is backwards. Would a gas gauge be polarity sensitive?
    Farmalldan
     
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    the 6v gauges seem to work with positive connected to them.

    I think it's not a very important symptom...
     
  13. 1953 chevy
    Joined: Sep 30, 2011
    Posts: 119

    1953 chevy
    Member
    from tucson

    Had this same problem on my 52 chevy truck the guage itself has lost its ground. Its been so long since I fixed it I forgot now what I did but after 11 years it still works.

    Sent from my LG-K550 using The H.A.M.B. mobile app
     
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  14. 52HardTop
    Joined: Jun 21, 2007
    Posts: 1,078

    52HardTop
    Member

    Have you tried testing the sender wire itself? With both ends disconnected and not touching any metal, try one end to a good metal ground anywhere on the truck. See if the sender wire is shorted or grounded.
     
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  15. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,230

    Mimilan
    Member

    This ^^^

    Then also check the resistance [from the terminal to ground] of the sending unit while installed. with the sending wire still disconnected .

    It is either a sending unit problem or wiring problem
     
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  16. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    @1953 chevy , @52HardTop , and @Mimilan - thank you for your suggestions! I will try to make some time tomorrow and try these and report back with my findings.
     
  17. I was recently stumped with the same problem after converting my 51 3100 to 12 volts. I used the original gauge with the runtz resister. Gauge was always showing empty with just a slight movement upon ignition. After much testing I finally discovered that the sender float had a tiny split and was filling with gas. Seems obvious but it took me a while to discover it. Replaced the float and all was good.
    Good luck, and I hope you get it resolved soon!
     
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  18. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

  19. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    The "sunk float" possibility is one I listed, definitely something to check for, it will trip you up easily!
     
  20. I wondering if the gauge being 6 volt, if 12 volts were run through it at some point, that gauge would be done for. At work, i get calls from guys that converted to 12 volts, but didn't put a reducer in, it burns the 6 volt gauge out pretty fast. ordinarily, an empty reading means bad ground
     
  21. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    listen guys, he gets a reading of Full when disconnecting the sender (infinite resistance), and a reading of E with the sender connected...the gauge itself is working!
     
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  22. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    EDIT: Something else I found, when I disconnect the sender wire from the sending unit and measure resistance between the disconnected end of the wire and ground, I'm getting somewhere in the neighborhood of 135 ohms. Not sure what that means, though.

    I didn't have much time today, but I disconnected the sender wire from the sending unit and then measured the resistance between the post on the sending unit and ground and got a reading of 11 ohms and change.

    Sometime this weekend I'm going to remove the sender wire from both the gauge and the sending unit so I can get it completely out of the equation. I'll then run a jumper between the gauge and sending unit and see what I get.

    Thanks again for all the feedback and help, folks!!
     
    Last edited: Jul 19, 2019
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  23. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    11 ohms sounds like the sender thinks you have 1/3 full tank of gas.
     
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  24. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    @squirrel That is about how much is in the tank right now.
     
  25. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    UPDATE

    So, I've found out that the gauge in my truck is a 12v gauge so no need for the Runtz.
    1. With the sending unit installed in the tank and hooked up, if I measure resistance between the sending unit post and ground KEY OFF, I get a reading of 5 ohms. As soon as I turn the key on, I get no reading at all.
    2. If I remove the sending unit from the tank (sending wire still hooked up) and lay it on the top of the tank and turn the key on, the gauge moves from E to F as I move the float. As soon as I reinstall the unit in the tank, it just stays on E (there is plenty of gas in the tank).
    3. I also tried running a jumper from the sending unit to the gauge (I wanted to be sure the actual sending wire wasn't grounding out somewhere) with no change.
    I'm really at a loss here. I know the sending unit works because I've bench tested it and it'll move the gauge as mentioned above in #2. I know the sending wire is good because I've run a new wire with the same results per #3 above. I know my 12v switched ignition source is good because I've measured the voltage at the gauge with a voltmeter key on/off (and because the gauge works per #2 above). I know the ground from the sending unit to the cab is good because I'm getting a resistance reading when testing between the ground and the sending post with key off per #1 above. What the heck else could it be??
     
  26. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    My guess is that the strap on the sending unit, that connects the terminal to the resistance unit, is shorting to the tank when you install the sender. Look where the mounting flange on the tank and the sender meet, see if the hole in the flange needs to be trimmed, or the strap needs to be bent away from the edge of the sender flange, so it won't make contact.

    Whatever is happening, it is that the sender wire is somehow getting shorted to ground when you install the sender in the tank.
     
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  27. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    Thanks, @squirrel . The strap was going more or less straight down for a couple of inches before bending outward and then bending back towards the resistance unit. I removed all the screws from the sending unit, but left it in the tank just resting on the rubber gasket and not touching anything else; I also disconnected the ground wire, but left the sender wire attached. When I turn the key on in this configuration, the needle jumps to F. As soon as I touch the ground wire to the sending unit mounting flange, the needle goes straight to E. At this point, I may just need to buy a new sending unit.
     
  28. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    Did you check the float to make sure it's floating?
     
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  29. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    @squirrel I will double check that in the AM. I did shake the float a few times when I had it out earlier to see if any gas was inside and didn't hear any sloshing around. But I'll take it out and test it in a little container of gas and check.
     
  30. Ty C. Denton
    Joined: Jul 10, 2019
    Posts: 44

    Ty C. Denton
    Member
    from Austin, TX

    So I finally got around to installing a new sending unit and the gauge seems to be working. I put a couple of gallons in and the gauge moved up. Next thing will be to fill her up and see what it reads. I'm a little gun shy filling it all the way up, though, since the last time I did it the pump shut off like it's supposed to, but not without a nice splash of gas out of the filler first. But I digress. Hopefully I can put this one to bed. Thanks to all those that chimed in with help and suggestions. Now I've got a leaky rear axle shaft seal, but that's for another post.
     

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