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Fuel Sending Unit Works Outside of Tank But Not In the Tank

Electrical and Ignition

  1. money pit

    money pit Well-Known Member

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    I have a 70 Barracuda. My gas guage reads a quarter to a half a tank after I fill up. Up to this point it was working fine. I tried replacing the sending unit (an OER unit). The same thing happened. I have a ground to the sending unit, directly from the battery. I tried both sending units outside of the tank, both seem to work fine. When I place the units back in the tank, they read the same as before. I checked the sending units with an Ohm meter, it's within specs. I know the guage works, I grounded the lead, it pegs the guage. Could there be something in the tank that is interferring with the sending unit? I read about the same problem on a number of forums but no difinitive answer. This is driving me crazy. Thanks
     
  2. 69hemibeep

    69hemibeep Well-Known Member

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    See if you are getting a full 5 volts past the limiter on the cluster. I had two from Redline that were 4.5 volts which equaled almost 1/4 tank
     
  3. money pit

    money pit Well-Known Member

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    I'm not familiar with the limiter you are speaking about. Where is it located on the cluster? Also, could my temp gauge be causing this problem? I read in a couple of forums that sometimes the temp and gas gauge have problems at the same time. I'm not using my stock gauge. Electrical issues isn't my thing, that's why I'm getting frustrated. Thanks again
     
  4. tonysrt

    tonysrt Well-Known Member

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    Also make sure your tank is grounded. Gauge won't work without ground.
     
  5. money pit

    money pit Well-Known Member

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    I have a ground directly to the battery. I check to make sure I Have a pulsing voltage at the wire that connects to the sending unit. Thanks
     
  6. 69hemibeep

    69hemibeep Well-Known Member

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  7. gs73rallye

    gs73rallye Member

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    Not sure if you have this fixed yet, I see it's a month old. There should be a ground strap that goes from the sending unit, to the fuel line on the body. The gas tank does not ground the sending unit. The rubber o-ring isolates it.
     
  8. tonysrt

    tonysrt Well-Known Member

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    On the sending unit, the metal ring that holds it in place should ground the unit. But use that metal strap on the fuel line also.
     
  9. money pit

    money pit Well-Known Member

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    I have the sending unit grounded directly to the battery. I found a modification on one of the other forums. I soldered a wire from the piece that holds the float to the pick up tube. Thanks for your reply.
     
  10. tonysrt

    tonysrt Well-Known Member

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    Did that wire solve your problem? There is a grounding strap internally in the sender. Check continuity from the top flange to the rheostat to see if you have very low resistance. I find it hard to believe 2 senders would have the same problem. But of course in this day & age with import quality being suspect anything is possible.
     
  11. money pit

    money pit Well-Known Member

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    I guess the issue with the fuel sending unit is a common issue. The modification that was on one of the other forums said that the sending unit is grounded only in one place on the rheostat housing. So although there may be an internal ground strap, it may not be good enough. It looks like the modification worked. It was actually the more expensive OEM unit that I had just replaced, that failed. Thanks for your input.