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55 Thunderbird Fuel Sending Unit


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I have a 55 Thunderbird 6 volt. I replaced the fuel tank and now the fuel gauge does not register. I have done all  the tests and from the results it  shows the problem is the sending unit. If  I take the unit out of the tank and ground it. it will work. If I put it back in the tank It will not work even if I ground with a wire.?????????Thanks in advance.

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When you test it out of the tank are you testing it upside down or the way it sits when installed?  Sometimes that arm moves away from the sweep and could cause it to read if upside down or if you are putting any sideways pressure when actuating a sweep.  The same could be the case when installed if it has play and in the tank moves away from the sweep.  Otherwise I would still lean on it being a ground issue.  I'm not sure if you can take it apart and see what's going on inside,  even if you have to drill rivets and re rivet it back together.  I was able to take the one in my 48 Plymouth apart and repair it inside, then rivet it back together.  It worked great afterwards. 

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13 hours ago, auburnseeker said:

When you test it out of the tank are you testing it upside down or the way it sits when installed?  Sometimes that arm moves away from the sweep and could cause it to read if upside down or if you are putting any sideways pressure when actuating a sweep.  The same could be the case when installed if it has play and in the tank moves away from the sweep.  Otherwise I would still lean on it being a ground issue.  I'm not sure if you can take it apart and see what's going on inside,  even if you have to drill rivets and re rivet it back together.  I was able to take the one in my 48 Plymouth apart and repair it inside, then rivet it back together.  It worked great afterwards. 

Hi auburnseeker, Thanks for your response. When I test it outside the tank  I hold it  as it would be in  the tank. I can ground it to the tank or the trunk floor and it will work. If I install it in the tank it does not work even if  I ground it to the same two places. The unit worked ok in the old tank. I do not want take it apart if I don"t  need to.       Neil

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Did you notice if there was alot of play in the arm when you have it out? There will be a little but it shouldn't be too much or it would be able to move away from the sweep as I mentioned.   Is the float shot so it sinks right to the bottom?  I think they are cork but if they are a brass cylinder maybe it's filling right up with gas.  Just guessing here.  

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30 minutes ago, auburnseeker said:

Did you notice if there was alot of play in the arm when you have it out? There will be a little but it shouldn't be too much or it would be able to move away from the sweep as I mentioned.   Is the float shot so it sinks right to the bottom?  I think they are cork but if they are a brass cylinder maybe it's filling right up with gas.  Just guessing here.  

Auburnseeker, The float is brass and  floats. No extra play in the arm.     Neil

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5 minutes ago, auburnseeker said:

Is your tank full, 1/2 or empty of gas? 

The tank has 10 gal. in it. When I can get the gauge to read  outside the tank, it reads  correct.  Neil

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I'm wondering if there isn't a dead spot on the sweep that happens to be right where the fuel level is.  Even if you activate it out of the tank you might go by it just fast enough though you may think you aren't going fast, that it doesn't really show.  Did you check the sending unit with an ohm meter and watch it as it sweeps? 

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21 minutes ago, auburnseeker said:

I'm wondering if there isn't a dead spot on the sweep that happens to be right where the fuel level is.  Even if you activate it out of the tank you might go by it just fast enough though you may think you aren't going fast, that it doesn't really show.  Did you check the sending unit with an ohm meter and watch it as it sweeps? 

yes  

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Did you run a jumper wire right from the back of the gauge to the sending unit in the tank?  Maybe it's an issue with the wiring in between or the gauge itself.  Did you check it on the gauge or just with an ohm meter when you had it out of the tank? 

Just shooting ideas and thinking out loud here. 

Edited by auburnseeker (see edit history)
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1 minute ago, auburnseeker said:

Did you run a jumper wire right from the back of the gauge to the sending unit in the tank?  Maybe it's an issue with the wiring in between or the gauge itself.  Did you check it on the gauge or just with an ohm meter when you had it out of the tank? 

Just shooting ideas and thinking out loud here. 

Did all of the above

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My friend said to check this. 

 

The arm may be touching something in the tank, he should ground the unit connect the positive side, then slowly lower into the tank while some watches what the dash gage does as he slowly lowers into the fuel.

Especially since it is a new tank.  He thought there could be a baffle in the tank possibly not in the original tank. All worth checking. 

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Is the car still 6 volt positive ground?  Maybe a pinched wire when you put the tank in? Though Bypassing that with wires directly to the gauge would eliminate that making sure of course you hooked the wires up the right way at the gauge if it's still 6 volt positive ground. 

Let me know what you do or don't find. 

Edited by auburnseeker (see edit history)
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5 hours ago, auburnseeker said:

Is the car still 6 volt positive ground?  Maybe a pinched wire when you put the tank in? Though Bypassing that with wires directly to the gauge would eliminate that making sure of course you hooked the wires up the right way at the gauge if it's still 6 volt positive ground. 

Let me know what you do or don't find. 

 The car is 6 volt Pos.  The wire is not in any position to be pinched. Gage is hooked correctly.  I rechecked the ohms. When the float is down it reads 12. When the float is raised  the numbers decrease. I am not sure what the numbers  should be, but they do not seem correct to me. I need to find what they should be.  Thanks for all your help so far.  Neil 

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On 5/10/2020 at 12:36 PM, auburnseeker said:

Curious if you figured out what the problem was? 

I have not worked on it   lately. I  don't know what to do  next.  Have tried everything.    Neil

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Just now, auburnseeker said:

Were you able to find Ohm Values online? 

Yes I was , it was  much higher  then what I was getting when I tested  for It. I am thinking of just biting the bullet and buying a new one  Neil

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