Fuel Level Always Reads Empty

Interior and Electrical

  1. Leizurtime

    Leizurtime Well-Known Member

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    1977 Plymouth Volare Wagon w/318. This has been an issue since I bought the car, as it sat for over 20 years and many of the systems have deteriorated. When ignition is off the needle of the gauge comes to rest far in the corner of the "E". Switching the ignition on the needle bobs up slightly, but not by much. It always remains in the same position no matter how full the tank is. Early on I had to pull the dash to change the indicator lights. I inspected the gauge and noticed the needle had become dismounted from its inner workings. It was a very delicate operation, can't believe how fragile their insides are, but I managed to fit it back together and reinstall it properly. Yet the gauge still reads empty.

    I consulted my Haynes manual and decided to do an ohm test off the sending unit leads. I tested it with the tank empty and the tank full. Both readings were around 75 ohms. This indicates to me that the sending unit only gives an empty resistance reading no matter how full the tank is. Problem is, I went and pulled a similar sending unit from a 77 Dodge Diplomat with a 318. They both operate by the same concept, but are set up for different gas tank configurations. The diplomat had a top port gas tank sending unit, my wagons sending unit port is low, near the bottom of the tank and it faces forward toward the differential. All the connections were the same though so initially I tested it and it gave 75-80 ohms @ empty and 11 @ full. It appeared to work properly, so I hooked up the diplomat sending unit to my wagon, grounded it and propped the float up to the full postion, but the gauge still reads empty :eek::confused:

    I also hooked up a test light to the guage wire and it would give an intermittent blip, don't know if that means anything. Tired of running out of gas without knowing when, lol. Its been impossible to adequately calculate the gas mileage with the carb in the state it is. I have to keep a gas can on me all the time.:cool: Anyone have experience repairing this system? Much obliged for your help, a Merry Christmas to everyone.
     
  2. Aspen500

    Aspen500 Well-Known Member

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    The blip of the test light is the cluster voltage regulator. It regulates to 5 volts basically by using pulse width modulation. That's a certain time on, a certain time off. The faster the pulse, the higher the voltage and vice-versa. It's similar to a dimmer switch in your house which just pulses the current faster or slower for bright or dim.
    I would check the resistance of the level circuit at the cluster. If it shows infinite, there's a problem in the circuit to the tank but if you had the "blip" at the tank, the wire is fine. If it's OK and varies with the float position, it has to be the gauge. Double check also that the contact in the printed circuit hasn't fallen out. I mean the part the studs on the gauge plug into. Also make sure the gauge ground is good at the cluster.
     
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  3. slant6billy

    slant6billy Well-Known Member

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    Ditto on that ground check. Unplug at the tank. You can back probe the signal wire from ground and it should push the needle to full. If not the gauge is of issue. I had to just add an extra ground wire to sending unit and it cleaned up the needle sweep without going any further
     
  4. slant6billy

    slant6billy Well-Known Member

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    This should explain it better:
     
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  5. Leizurtime

    Leizurtime Well-Known Member

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    I tested the blip at the gas tank connection. The blue wire that connects to the sending unit housing. Hooked the tester lead to the gas tank ground (one of the fuel lines) and thats how I got the blip. I wanted to make sure it was sending some kind of signal. So with the blue wire grounded it should read full. I think I tried that with the light and the needle still didn't budge. I'm also worried about the ohm reading of the sender itself. It read 75 ohms at both full and empty. There could very well be a problem with both the gauge and the sending unit. Which troubles me, because my research indicates that it is really hard to find a sending unit for my particular car. Its the Calif emissions with two fuel lines design and even then, most new ones sold are of the top mount variety. Not side mounted like mine. Is it possible to Frankenstein the diplomat sending unit with mine?
     
  6. Aspen500

    Aspen500 Well-Known Member

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    You certainly could have two separate problems. If the car sat for 20 years it's almost a guarantee the sending unit is shot. Worse if the tank sat with fuel in it all that time. It's probably corroded beyond all recognition.
    Leave the test light out and ground the blue wire straight to a good ground. As mentioned, if the gauge doesn't show full or close to it, the gauge is bad.
    Good news is fuel gauges are fairly easy to come by, unlike the early style sending units, especially with CA emission.

    I take it you have the "hump" tank? Don't quote me on this but you MAY be able to Frankenstein it by taking the sending unit off and adapting the good one. I'd almost have to have them side by side to see if it's possible though.
     
  7. F body Deconstructor Jim

    F body Deconstructor Jim Well-Known Member

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  8. Leizurtime

    Leizurtime Well-Known Member

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  9. F body Deconstructor Jim

    F body Deconstructor Jim Well-Known Member

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    you could use it for parts to fix yours.
     
  10. Leizurtime

    Leizurtime Well-Known Member

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    Already looking at it to see if I could modify the second port. Idk, I'll have to pull mine and inspect its configuration. Good looking out though.
     
  11. F body Deconstructor Jim

    F body Deconstructor Jim Well-Known Member

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    it will physically fit your tank so the rest is just swapping parts.
     
  12. Leizurtime

    Leizurtime Well-Known Member

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    I wonder how they secure the actual measuring device to fuel inlet tube. It doesn't appear to be welded, but maybe soldered some how. Thinking of grinding off the float sensor mechanism and attaching it to mine, but I wonder if welding maybe too hot. It could damage the internals of the float sensor. Any thoughts?
     
  13. Leizurtime

    Leizurtime Well-Known Member

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  14. Aspen500

    Aspen500 Well-Known Member

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    I believe the sending unit bracket is spot welded to the tube. Don't recall how the sending unit card is attached to the bracket though. Probably tabs that get bent over or something like that(?)
    You can add a vapor tube to the single tube unit. Drill a hole so the tube slides in tight and then solder it in. Either use the tube from the old unit, if possible, or make a new one from fuel line tubing.
     
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  15. F body Deconstructor Jim

    F body Deconstructor Jim Well-Known Member

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  16. BudW

    BudW Moderator Staff Member

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    The wagon fuel tank is the same as the car.
    ’76 to mid-year ’77 are the same tanks then late ’77 to ’89 FMJ tanks should all be the same.

    Fuel senders are different between the two year breaks and between CA and other.

    I wouldn’t do this to an old sender, but you can make a new vent tube and weld it (or epoxy it) into/onto a new sender to make a non-CA sender into a CA sender.

    Swapping the electrical guts is about the same amount of work.
    I think I would rather get the new sender, and add a tube to it.


    Note: pretty much all fuel senders from early ‘60’s to mid ‘90’s use the same resistance, so getting your hands on “a” or “any” fuel sender and plug it in, then have a 2nd person watch gauge (or move sender) to see if problem is sender or gauge (or other).

    Testing power at the sender will give you a false reading.
    The 5 volt voltage limiter does work on a slow pulse – which works fine, sense senders don’t change readings that fast – but doesn’t help for testing purposes.
    BudW
     
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  17. Leizurtime

    Leizurtime Well-Known Member

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    Anyone able to tell me the size of the rubber fuel hose coming off of the tank at the sending unit?
     
    Last edited: Jan 2, 2017
  18. BudW

    BudW Moderator Staff Member

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    The newer FMJ's used three different fuel lines/hoses.
    5/16” for main fuel line.
    3/16” for return fuel line
    1/4” for vapor line (going to charcoal canister from tank).

    Not sure for '77 – but would guess 5/16” and 1/4” only.
    BudW
     
  19. Leizurtime

    Leizurtime Well-Known Member

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    I don't doubt it, but when I bought the car, whatever fuel it once had evaporated long ago. Nearly every system has deteriorated on the car. The guy I bought it from was afraid to put gas into it to start it, thought it might clog the carb with varnish. I just put on a new fuel filter, put a gallon in the tank and it fired up. Heres what it looked like when I first came upon her.

    00w0w_lcLq2h2mKkD_1200x900.jpg
     
  20. Leizurtime

    Leizurtime Well-Known Member

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    Got the new sending unit you guys mentioned, should be here on Monday. I'll try to post some pics of the different ones that I have when it gets here. So, you believe its safe to solder a new tube into the new sending unit cover? That will be strong enough and seal it well too or should I have someone weld it on? This thing mounts near the bottom of the fuel tank, wouldn't want to have any issues with it.
     
    Last edited: Jan 20, 2017