76 Nova reading full gas?!?
 

Got a 76 Nova concourse 350 engine and 350 trans. Recently started up the car and gas shot up past the full point and won't come down? I don't want to just start replacing s**t, so i decided to jump on here for suggestions. First thing that came to mind was fuel sending unit. Car is 35 years old so, it was my first assumption. Suggestions/troubleshooting methods?

its a super simple system. its pretty much down to the sending unit or the actual gauge. My vote would be for the piece thats been sitting in gasoline for almost 40 years.

Test the sending unit with a multimeter set on ohms. Connect the black lead to ground and the red to the terminal like in the pictures I attached. This is an old one I have for the Chevelle. I'm pretty sure yours is 0-90 ohms like mine is but it might be 0-30. When the tank is full (arm up) it should read 90 ohms. When the tank is empty (arm down) it should read 0 ohms. As you can see mine is a little off.

Ground the gauge signal wire at the tank and see if the gauge reads empty.

A open circuit will cause the gauge to max out "full" on the dash. A short to ground will cause it to read "empty" If you ground the signal wire and the gauge reads empty, it would indicate the sending unit is faulty.

Cool, thanks for the input guys. I'm going to drop the tank this weekend and I'm betting that's going to be the problem. I'll snap a couple pics along the way, hopefully one of them will be the gas gauge working lol.

When you're done fixing that fuel gauge come over and fix the one in the 87 for me

Lol i had to do it for my 89. It was a pita, because i had just filled the gas tank up and my pump died.

My sender works, but my float has a hole in it. I'm gonna need to install the 255 so i'm just waiting to replace it.

Brings back memories, that was my first car, a hatchback I bought off some ol' lady for 100 bucks with an inline six in it, dropped a toilet 350 out of a van into it...what a mistake...cool car though, blacked it out with chrome rally repros and all the babes were into me...ok last part's a lie.

Disconnect the tank sender, use a 12v testlight. Probe the wire and ground the clip to a known good ground. Key on, the testlight should "glow" and the gauge read about 1/2 scale. That proves the gauge itself and the wiring. Old time dealer mechanic trick. Any GM electrical gauge= water, oil, fuel can be quickly tested like that.