How to find why fuel gauge doesn't work?

[rsgt]

Originally Posted by Freestate

I'm going to piggy off of this thread as I'm having similar issues. I have not started diagnosing the problem but wanted to see if I could get some expert advice as to where I should start.

Issue: When the gas tank is full, the fuel gauge will read just barely over 1/4. As the tank gets empty, it will drop to 1/8. I've never let it get below that before filling. My first thought would be to check the float. Thoughts? Should I check something else first before pulling the float out?

Freestate, Mine was just like yours. Passed 1/4 tank when full then went down as gas was used. Here was the fix: http://67-72chevytrucks.com/vboard/s...d.php?t=744066

[VetteVet]

Originally Posted by demian5

Work smarter, not harder.

Pull the wire off the sender, turn the ignition on and ground the wire to the body. It should go to full.

High resistance equals more fuel and low resistance equals less fuel. Grounding the wire will give less resistance. I think you will find the gauge will read empty.

Remember, when the tan wire is off the sender the gauge reads past full because of the high resistance to ground AKA infinity between the wire and ground.

The temperature gauge works just the opposite, when you ground the sender wire the gauge goes to full HOT. Perhaps you had them mixed up.
I have done it myself, because they are so similar. VV

[demian5]

Originally Posted by VetteVet

High resistance equals more fuel and low resistance equals less fuel. Grounding the wire will give less resistance. I think you will find the gauge will read empty.

Remember, when the tan wire is off the sender the gauge reads past full because of the high resistance to ground AKA infinity between the wire and ground.

The temperature gauge works just the opposite, when you ground the sender wire the gauge goes to full HOT. Perhaps you had them mixed up.
I have done it myself, because they are so similar. VV

Ah, right. i'll go back and edit. Yeah usually its the temp gauge people have issue with. Thanks!

[Freestate]

Originally Posted by rsgt

Freestate, Mine was just like yours. Passed 1/4 tank when full then went down as gas was used. Here was the fix: http://67-72chevytrucks.com/vboard/s...d.php?t=744066

Awesome! Thank you for the tip. When I get a chance to do some diagnosing I'll let you know if that was the problem.