flyingethan

I know that this subject has been beat to death but I haven't found a thread that helps me with my possible unique problem.

I have 1970 Cutlass Wagon.

I have the same problem with my fuel gauge that others have. It reads way past full all the time. I ran a makeshift ground from the back of the gauge to the chassis, plugged my gauge back into the wiring harness and the gauge went to empty. I thought "cool, I found my problem". I removed my makeshift ground and remounted the gauge to the instrument panel as it should be.

I jacked up the car, removed the back tire and removed the stone shield. The ground wire from the sending unit appeared to be a little corroded so I unscrewed the ground from the body where it is attached and cleaned it. I lightly sanded the ground lead.

I decided to see what the gauge was reading with the ground disconnected. The fuel gauge went to a quarter of a tank when I turned the ignition on. I didn't start the car I just turned the key to accessory position. A quarter of a tank is about how much gas in it so it was reading correctly (or close enough to correct). I thought that was weird because the ground was disconnected from the fuel sending unit.

So I re-connected the sending unit ground wire to the inner body wall like it was before. The fuel gauge was still reading a quarter of a tank when I turned the ignition on to the accessory position. I thought "awesome, the car is fixed" even though it was reading correctly with the ground wire not attached and attached. But who cares, it's working.

I put the stone shield back on, the tire back on and lowered the car back onto the ground and went inside my house for a little while. I came back out a little later to start my car and move into the garage. When I started my car the gauge went back to way past full again. Now I thought "what the hell it must be the a crack or slight break in the fuel sending unit main wire that goes from the sending unit to the dash.

So, since my main sending wire from the sending unit has already been spliced, back by the rear bumper before it goes into the main wiring bundle (somebody before me spliced it), I thought that I could just separate the wire in two and run a makeshift sending unit wire up to the dash just to test it.

I ran a wire around the outside of the car from my sending unit to the back of the fuel gauge. With the fuel gauge plugged into the wiring harness as it should be with the new sending unit wire temporarily replacing the tan/ beige old/ original sending unit wire I turned the car on and the the gauge remained at way past full.

I undid my splice and returned the wiring to the way it should be, re-installed the gauge the way it should be and it still reads way past full.

I did all of this this past weekend. In the past month or so the gauge has appeared to read correctly a couple of times but only momentarily.

SO, any thoughts?

Bad sending unit? Bad gauge? Loose wires at the top of the sending unit (which I have not inspected yet because that means removing the tank to get to it)?

oldcutlass

The fuel gauge does not work in the accessory position. Take the wire off the fuel sender, ground the wire with the key in the "on" position and see if the gauge goes to E. If it does there is probably an issue with the sender.

MDchanic

You beat me to it, Eric.

+1 all the way...

But be sure to really carefully check the connections from the gauge wire to the sender and from the sender to ground.

- Eric

Fun71

Agreed.
I had the same issue with my '70 reading way past Full. I dropped the tank and discovered the main sending unit wire was loose on the sending unit stud. I tightened the push-on connector with pliers so it was tight on the stud and that solved the problem.

flyingethan

Thank you guys. I will work at it some more this weekend. I appreciate y'all's input.