1. MoJo

    MoJo New Member

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    Before posting, I always search the forums for suggestions to help resolve any issues on my 1966 300. I followed all the posted suggestion and still cannot figure out why the fuel gauge is not working. In any event, I trying to troubleshoot why my fuel gauge reads empty all the time. Below are the steps and results I've done so far in trying to resolve the problem:

    1. Checked an verified all fuses are good
    2. Put temp ground jumper on fuel sending unit body and tested ground with test light all the way back to the battery to verify good ground - Result, no change in the fuel gauge
    3. Put test light on sending unit wire at the tank and got a pulsating light on the tester
    4. Put ohm meter across the fuel sending unit connector stud and unit ground and read 31 ohms
    5. Grounded out the fuel sending wire and gauge swings over to full when i turn on the key.

    So, I've got a good ground at the sending unit, pulsating voltage on the wire at the tank which indicates the voltage limiter is working, 31 ohms through the sending unit and I verified the gauge works when grounding the wire at the tank. It should be reading 1/3 to 1/2 of a tank, but only shows empty. Of course, this sending unit was new when I installed it last year and hasn't worked from day one. Any thoughts?

    IMG_3823.JPG
     
  2. Mudeblue

    Mudeblue Member

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    If it is the same gauge as the 65 Plymouth; new field gauge. Fought that problem for years and gauge was problem. Resistor in fuel guage!
     
  3. rkrochen

    rkrochen Well-Known Member

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    Sounds like a bad tank sending unit. Could be the float is leaking and saturated.
     
    • Agree Agree x 2
  4. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    There's a lot of extra nonsense in this thread, but here is what I did to diagnose and correct my gauge issues.
    Gas Gauge Fix
     
  5. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    As noted, you probably have a bad sending unit float. Pull the sending unit and rattle the float, if you hear liquid sloshing inside, it is a defective float. This must be fairly common because I have run across 3 like that in the last year. Floats are made overseas, so probably just more of the usual Chi-Com crap.

    Dave
     
  6. MoJo

    MoJo New Member

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    Thanks for the suggestions. My confusion is the ohm reading vs the gauge indication. I think i'll try another sending unit or possibly a 100 ohm potentiometer to test the gauge function.
     
  7. traintech55

    traintech55 Senior Member FCBO Gold Member

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    The fact that grounding the sending unit wire makes the gauge move tells you it is in the float. Did you replace the ground strap with the new float assembly? If you did then it is the float.
     
  8. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    The magic numbers for that are 10 ohms for full, 23 ohms for half and 74 ohms for empty.
     
  9. 73Coupe

    73Coupe Senior Member

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    I tried asking for the resistance readings from a few vendors on ebay before purchasing their overpriced new or NOS senders. Especially since a lot of them are listed "no returns".

    The responses I received were either crickets or an "FU".... so I didn't bite.

    So for now I am still relying on my "new" but barely functional sender. Fook.
     
  10. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    As far as I've been able to figure out, there is only one offshore manufacturer building the pickup/sender. Spectra seems to be the largest importer/distributor but I don't think they are actually manufacturing them. I you'll notice, the part number is pretty much the same across all the vendors.

    I really think the answer is a "work around" with the Meter Match adding the corrections or fudge factors to make the gauge accurate. See the link I listed above for my experiences and a link to the Meter Match. IMHO, that would correct for both the sender characteristics and an aging dash gauge. It does require a more constant power, so an electronic voltage limiter is needed, but I think the old mechanical limiter is often part of the issue too.
     
  11. Polara_500

    Polara_500 Senior Member FCBO Gold Member

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    Hey, I have three new senders with good ohm readings, the only problem is none of them fit my tank. So there's other ways to mess it up, as all the vendors sold me units for my specific vehicle.
     
  12. MoJo

    MoJo New Member

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    Big John, I saw those ohm reading you posted in another thread and thinking is with a reading of 31 ohms, the gauge should show some movement. If the ohm meter showed 100 or more ohms, then I could understand the gauge reading. Remember, when I ground the wire, the gauge swings to full so I know it's working. Perhaps it is a combination of failing voltage limiter and crappy sending unit. The Meter Match device looks promising and I will definitely look to install one to get the gauge to read accurately, however, it's not reading at all, it's pegged all the way past empty. The sending unit is a Spectra product purchased last year when I installed a new tank. I should have tested it before installing. I'll keep digging and see what i can find out. Thanks for all the input.
     
  13. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    31 ohms should give you something around 1/4-1/3 on the gauge.

    That tells you the wire is intact, and the gauge moves. Not necessarily working right though.

    The sender gets blamed for everything, but I don't think it's the case here. It may be off, but if you are getting a reading of 31 ohms, that tells me it's working. Any idea how much gas is actually in the tank?

    The 100 ohm pot idea is pretty good. It would work like my decade box and you can check the gauge. If it's like my '70, there's a plug under the driver side kick panel/door threshold trim that you can unplug to connect your pot and not have to crawl under the car. I really think that is what you need to check.
     
  14. MoJo

    MoJo New Member

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    Big John,

    The gauge reads past empty and never moves regardless of the amount of gas in the tank. The 31 ohms reading was with about 1/2 full tank. I just refilled the tank and will get a new reading to see if it changes and I'm picking up a potentiometer today to test the gauge function and accuracy. I'll post the results.