One gas gage reads full all the time

[mlan12]

I have a 79 F-250 with two tanks. One tank the gage seems to be working properly. The other gage reads full at all times. Both gages were working proerly. I shut the engine off for a few minutes, when I restarted the engine one gage read full. Both tanks are about one fourth full. The selenoid valve selecting fuel supply source seems to be working fine. Any suggestions on how to trouble shoot this problem will be appreciated.

 

[Skitter302]

Welcome Mark,

Double Check that the sending wire isn't grounded out. You can do this by using a continuity testing probe. When you do this test, the Key has to be ON but the Engine can be OFF. If indeed the wire is grounded out, look for the place were the wire shielding could of chafed off. This could mean dropping the tank if you don't find anything on the outside of the tank. If you indeed have to drop the tank, unplug the sender and test for continuity before replacing the sending unit.

Best of luck to ya.

 

[mlan12]

Skitter302, thank you for your advice. I would like to clarify how to do the continuity test. If the wire is grounded does this mean I will not see any voltage on the wire?

 

[Skitter302]

Sorry for my late reply,

The wire is grounded out you should see no voltage, and if it isn't you should see some voltage.The sender works on resistance, the fuller the tank the less voltage, so an empty tank is closer to ~5volts.

See if this page helps you http://www.fordification.com/tech/fuel-sending-units.htm

 

[mlan12]

Thank you for your help.