fuel gauge question

[TERMN8OR]

I have a stock tank in my 69 camaro that was sumped. I'm running an autometer fuel gague...
When I fill the car up with gas, the fuel gauge only will go up to 3/4. What would cause this ? Do you think my sending unit is bad ?

[TERMN8OR]

anyone got any idea's about this ?

[CarlC]

1) Disconnect the sending unit wire from the plug located in the aft trunk.

2) Connect a jumper wire to the empty plug in the main harness.

3) With the jumper wire not grounded, turn the ignition key on. The gauge should go past empty.

3) If the gauge does go to empty, ground the jumper wire. The gauge should go past full.

If the gauge does not pass these tests, then something is wrong with the gauge.

If the gauge does do these things, then the gauge is fine and hence something is wrong with the sending unit.

Removal of the sending unit from the tank will be required. With the sending unit removed connect the body of the unit to ground, and the output to the body plug as noted above.

Move the float arm up and down. At full up the gauge should read past full. With the float arm full down the gauge should read empty.

If it does not go all the way to full then the sending unit is likely faulty. It should have a zero ohm reading empty, and 90 ohms full.

[TERMN8OR]

I tested the gauge and it's working fine... I guess I need to drop the tank now to check out the sending unit.

[esenior]

The same thing has happened to me. Dropping the tank was a pain, but replacing the sender fixed the problem.

Has anyone put a meter on their gauge before mounting their tank? Is it as simple as manually moving the arm, or does it need to be mounted in the tank? Any recommendations?

[CarlC]

It can be moved by hand but it must be grounded to the chassis of the car in order to work.

Most sending units have a range of approximately 93-94 ohms high/ 0.5 ohms low.