Hi everyone! This is my first post on this forum and I have a question about a gas gauge on a 78 El Camino my buddy just bought.

The gauge works fine BUT reads incorrectly. When the gas tank is filled up the gauge goes way past the full mark but when the tank is empty it shows there is still a quarter of a tank left.

I was told to unhook the hot wire at the sending unit on the tank and that it should go way past the full mark, WHICH IT DID, then to ground the hot wire and it should go to empty. If it does they said, that means the sending unit is bad.

Well, it only went to the quarter tank mark instead of empty. Does this mean the gauge is bad, or is the sending unit bad?

As I said before, the gauge works fine, but its almost like the needle was put on wrong as its exactly a quarter of a tank off in its reading.
SO, what do I do, change the gauge or the sending unit? Can the needle be removed and put back on in the correct place? Thanks in advance for your help. :cry:

Hi everyone! This is my first post on this forum and I have a question about a gas gauge on a 78 El Camino my buddy just bought.

The gauge works fine BUT reads incorrectly. When the gas tank is filled up the gauge goes way past the full mark but when the tank is empty it shows there is still a quarter of a tank left.

I was told to unhook the hot wire at the sending unit on the tank and that it should go way past the full mark, WHICH IT DID, then to ground the hot wire and it should go to empty. If it does they said, that means the sending unit is bad.

Well, it only went to the quarter tank mark instead of empty. Does this mean the gauge is bad, or is the sending unit bad?

As I said before, the gauge works fine, but its almost like the needle was put on wrong as its exactly a quarter of a tank off in its reading.
SO, what do I do, change the gauge or the sending unit? Can the needle be removed and put back on in the correct place? Thanks in advance for your help. :cry:

It's sounds like a gauge problem from what you describe.

You are doing just fine with your testing. Try one more test. On the back of the meter there should be 3 wires. Black is ground. Tan is the tank sender wire. Pink is 12 volts. Short the tan connection directly to ground. Suspect that the gage still will read 1/4 tank instead of empty. Your same problem as you have seen. Confirms a gage that is off.
Now on the back of your gage there is a white ceramic piece across the terminals. This is a calibration resistor. Suspecting it has gone bad.
Look at the junkyard for another Chevy meter around the same size. Mid 70s trucks should have one. Take the calibration resistor off (pay for it) and replace it on your meter. Good chance your meter will work again.

Thanks John, I appreciate the help.

It's also possible that you have a bad ground from the instrument pod. Though that calibration resistor is more likely for the symptoms you report.