[mopartner]

The fuel gauge does not work on my 70-Challenger. I think it has the wrong sending unit. The car has a small block which would not have a return line port on the sending unit. The unit on the tank is new and has the return port that is blocked off. Could the sending unit be the Problem?

[Moparman1972]

Even if its the wrong sending unit, it should still make the fuel gauge swing wildly or jump to the extremes of the gauge. Might be your wiring. Did you clean the plug that goes on the sending unit if it was unplugged for a length of time? Mine was corroded and required cleaning with a pipe cleaner to get a good connection. The sending unit also needs to ground back to the body.

[72challengerorange]

My replacement sending unit came with a second port. Check the ground strap as MM72 said.

Tom

[mopartner]

I will check the connection and the ground. If it is a bad gauge will it have to be rebuilt or is a new one available?

[dave-r]

First of all. Forget about the return line pipe. Blocked off is fine.

Second. If the sender unit is faulty you will need a new one. Easily found.

Third. In the very unlikely chance that it is the gauge itself I think I have a spare somewhere.

But chances are it works fine and you have an electrical problem.

First check that the earth strap over the rubber hose section of the sender outlet is clean and making good contact.

Next test the gauge in the dash.
To do this remove the lead from the sender and touch it to a good chassis ground with the ignition switched on. Just touch it long enough to see if the needle jumps up. Keeping it shorted to earth will burn the gauge out as it operates on less than 12 volts.

Last of all remove the sending unit from the tank and connect a ohmmeter between the body of the sending unit and the terminal in the center of the unit.

With the float in the 'empty' position you should get a reading of 73 ohms (+/- 12 ohms).

In the full position the reading should be 9.6ohms (+/- 1 ohm).

These tests will narrow the problem down.

If the fuel gauge does not work when you test it the most likely problem will be the low voltage supply from the dash. The fuel gauge works on a much lower voltage than the rest of the car. It is a safety thing. You wouldn't want a spark in the fuel tank sender. The circuit for that sometimes breaks.