Gas gauge Issues

[bladerunner]

My gas gauge is acting weird.  When the truck is off, the gauge needle just kind of sits at a random place (always has). Once you hit the ignition, the needle will travel to the correct position. Not sure if that is normal or not.

Anyway, lately the gas gauge has been reading flat; the needle is all the way to the right.  Once I turn the truck off though, the needle will slowly move back to about 1/3 full position. I haven't looked that much into this as I stink at electrical work, but I hope to this weekend. Any ideas?

[zieg85]

If it is reading past full, about 3 o'clock that usually indicates there is a bad ground.  As far as the other tendencies you mention some of my trucks act that way, some haven't.

[bladerunner]

Does the gas gauge ground via the ignition?

I only ask as I have had intermittent issues with the engine not turning over (literally just started this morning).

[zieg85]

Gas gauge is grounded at the tank, a wire on the sending unit...

[bd]

The fuel gauge uses three connections: 12V Ignition, Constant Ground and Sender.  Ignition and constant ground provide a fixed magnetic field inside the gauge.  Ignition and sender (which is actually a variable ground inside the fuel tank) create a variable magnetic field inside the gauge.  Interaction of the two magnetic fields controls needle position.  As Zieg said, your symptoms are characteristic of an open sending unit, sender wire or sending unit ground connection, etc.

Does the gas gauge ground via the ignition?

I only ask as I have had intermittent issues with the engine not turning over (literally just started this morning).

Ignition is necessarily insulated from ground. 
Based on your engine not cranking, check your battery grounds to engine and frame.

[bladerunner]

Well I did not get to the gas gauge issue as I was tackling the crank issue.  I narrowed the problem down to a faulty neutral safety switch.  I did not figure it out in time to go pick one up, so hopefully tomorrow or Monday.

[Captkaos]

Did you search the Technical forum?  This comes up a lot.  There is a whole post devoted to it:
http://forum.73-87chevytrucks.com/smforum/index.php/topic,9072.0.html

[bladerunner]

Thank you Chris

[Elpresidente]

My gauge on the passenger side tank reads way past full at 3 o'clock, would the ground issue likely be the ground wire from the sending unit to the frame?

[Captkaos]

Not saying this is what is wrong, but most of the ones that have the gauge at 3 o'clock that I have worked on the sending unit has to be replaced as it was shorted out.