My fuel guage is acting up. When I fill my truck up with gas it goes all the way up to full and stays on full until it gets to 3/4 of a tank then goes to empty and stays there any idea's

 

Mines similar. Probably the sending unit. Its supposed to vary the ohms resistance at level changing liquid measure into a electrical current to be read at the gage. Its either wore out or maybe has a pinhole in the float that allows it to float at full but has enough gas in it to make it sink when the pressure evens.

Anyway they are about $60 at lmctruck.com . While youre at it hit up a junkyard and get a filler neck from a 87-96 truck. This will fix the slow pumping at the gas pump if you have that problem.

 

I have had a similar issue since I bought and got my truck running. I put a new sending unit.The fuel gauge when filled up reads 3/4. And it seems to go to E faster than it should. I just have to look at how many miles between full ups to know when I need gas. I would really like the gauge to read correctly. The truck only has the rear tank with an electric fuel pump. I dont know if that has something to do with it or not.

 

Probably got a unit for a 16 and have a 18 or got a 18 and have a 20 or some combo of that.

 

Thank you, I will have to check that out.

 

This page shows 2 tanks. A 22.5 and a 20.5 for side mount tanks.
http://lmctruck.com/icatalog/fc/full.aspx?Page=40