Gas Gauge Only Reads Half Full

Im having a trouble figuring out why my gas gauge only read half full when topped off and empty with 5 gallon still in the tank. I have a late model cj 15gal plastic rear mounted gas tank with a mts sender and autometer gauge in the correct ohm range. I dropped the tank yesterday and took the sender out and connected the sender wires. The gauge seemed to read correctly when moving the float by hand but once reinstalled into the tank it wont read higher than half. Im going to pull the tank out again this weekend, how should i check and adjust the sender and gauge?

 

I had an experience like that with my '76 jeep. I removed the fuel sender from the tank and tested it with a multi-meter. It worked fine. I connected the sender to the gauge circuit but the fuel gauge didn't read properly when I manually moved the sender's float. I tracked down the problem to the ground wire. The ground went through a corroded connector. A wire from that connector was attached to the undercoated frame with a rusty screw. The fuel gauge measured the added resistance of the poor ground with the variable resistor of the tank sensor. I fixed the poor ground with a stainless steel screw and the fuel gauge then indicated the correct fuel level.

 

Does your tank have a baffle inside that the float may be hanging up on? Also as stated above maybe a bad ground.

 

Test with resistors as described in the TSM. This will verify that the gauge and wiring from the gauge to the tank are working properly. Then you can focus on the sender function.

 

Mine reads similar. My grounds are good and I matched the gauge to the sender. It should read fine, but it reads close to empty with 5 gallons or so. I could bend the float arm or do something else, but since it reads empty with gas in it, it does the job I need it to. If it was still underseat I could just look in there to see if I had fuel.

 

I had the same problem with mine. Grounded the tank, but no success. So I bent the arm on the sending unit. Reads spot on now.

 

This should be part of the installation instruction. My tank depth is 6 inches and the float arm coming out of the shipping box was bent to about 8 inch depth. Bent arm for proper depth and works good.