Gas guage trouble shooting

[billyk]

I have a 1980 GMC Sierra Classic 1500. I have installed a 350 Vortec and as a result installed an electric fuel pump. I have duel gas tanks and believe I am only drawing out of one side. Both tanks show full but I know the one that is being drawn on is not full. This false reading just occurred when I ran out of fuel.
Any suggestions on what to look for?
This is my first thread.
billyk

 

[wildhorsehans]

If you think it is a gauge issue. with the ignition on, pull the wire off the fuel sending unit. If the gauge goes to empty you have a shorted sending unit, if it stays at full you have a bad gauge or a short in the harness.

 

[1948]

are you running each tank to the same gauge? if its not unswitched from the other side it will mess with the resistance and screw up the reading(thats how a gas gauge works, ohms of resistance)

 

[Gary S]

The fuel transfer switch dictates which tank you are pulling fuel from, and also at the same time, which tank the gauge is reading.

You did put in two fuel pumps, didn't you? You should have one in each tank. And, the fuel transfer solenoid needs to be fully connected the factory way and working, or your gauge won't work.

 

[Gary S]

If you think it is a gauge issue. with the ignition on, pull the wire off the fuel sending unit. If the gauge goes to empty you have a shorted sending unit, if it stays at full you have a bad gauge or a short in the harness.

NOT on an old GM vehicle. Disconnecting the sender and turning on the ignition will cause the gauge to read all the way past Full up to the mechanical stop. On most gauges, that mechanical stop will be somewhere near the 3 o'clock position on the gauge.

 

[Canadian Cowboy]

NOT on an old GM vehicle. Disconnecting the sender and turning on the ignition will cause the gauge to read all the way past Full up to the mechanical stop. On most gauges, that mechanical stop will be somewhere near the 3 o'clock position on the gauge.

You are correct and if you ground the sending unit wire to a good known ground the gauge needle should go all the way down below empty.

CC