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Recently, each time after filling the tank, the gas gauge will stay on full for a longer than normal time and then as the tank empties maybe after 100 miles or so, the needle starts jumping around a whole bunch and does so until the tank is actually around a quarter full, and then it settles down and registers a quarter tank. Is this the sending unit or a ground problem? If it is a ground problem, where is the ground? Thanks, Rich
 

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OK...you win.....

Wonder if the float on the sender came loose? I would pull the sender and have a look at it. If it was a ground problem, it would go past full and stay there.
 

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The sender has a ground wire from the body of it to the frame. There is also a sender wire to the gauge. If the ground wire is loose, the gauge will generally go way past full and stay there, so I don't think that is your problem.
 

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Doc here, :pimp:

Sounds Like you have a Worn carbon Contact on the Fuel sender Variable Resistor..To check remove the sender,Get your DVOM out, set it for RX1, calibrated to 000, it should read somewhere between 000 and about 300 ohms, or visa versa, SLOWLY move the float assembly up and monitor the meter, it should climb (or decrease) it's Ohmic value in proportion to the movement , this should be a smooth reading with no "Jumps" or dropouts, If you have any, it is bad, replace, or just replace since it's already out..

If you have no ground to the tank, you may be losing the sender ground under "Body Flex" the tank sits on Rubber mat, the lines , (usually) terminate into rubber hose, around the pump or filters, so the tank is Isolated ABOVE ground. You need to install a PROPERLY bonded ground, burnish the frame side, and use STAR washers, and on the tank side, look for a ground lug at the fuel line/sender egress panel.

That should cure your problem.

Doc :pimp:
 
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