Hello, I have a 1994 Pontiac Firebird Formula. Some of you may recognize me from previous threads, but if you don't know I have been restoring this car to be road worthy for about a month now. It had been sitting close to 12 years.

I replaced the fuel sending unit and fuel pump all at once when I first got this car. They were both bad and keeping the car from running (obviously). The new fuel sending unit worked fine.

I recently have been driving on the road and the fuel gauge jumps an awful lot while running and will even show all the way past the full line. From experience I know that this is caused by the fuel sending unit circuit not being completed. It always works however when I start the vehicle later.

The fuel pump still works when this happens.

Does anyone have an idea of what might be causing it? I don't know much about it so I thought maybe somebody had an idea of where I can start looking before I pull the fuel pump assembly back out.

 

Bump...

 

Is it like a really quick jump or a slow jump? If its really fast and twitchy when it moves I would look for a loose wire or connector somewhere. I have a 93 T/A and the gauge will move up and down quite a bit once it passes under 3/4 of a tank. If it happens under acceleration, braking or turning it sounds like it may be normal. It's just caused by the sending unit moving up and down due to gas sloshing around in the tank at the time.

 

It works on and off, not just jumping up and down.

 

Gm thought gas gauges were For pussies, overrated and wouldn't matter in the future so they didn't do enough R&D in f-bods to provide an accurate one OEM.
super glue the needle to say full all the time if it bothers you.
OR
Print this and tape it to your dash:
Gauge Past full=full, on full=3/4full, 3/4full= half tank, half tank= 1/4tank , 1/4tank= 1/16 full , on/near E= your probably walking already

I've began treating half tank as empty

 

The fuel sending unit and the fuel pump are not OEM, they are aftermarket.

 

Per GM design, the tank shape is the culprit.

 

I don't care that it doesn't read right, It doesn't read at all. the circuits not being complete and it's not being caused by the the circuit inside the gas tank.

 

It was a loose connector on the undercarriage, where the circuit goes into the floorboard. I fixed it with aluminum foil. As I had just said, the whole assembly in the tank was new and aftermarket.

My gauge works fine, has about two gallons left on E and is on the F line after fill up. As for your fuel sending unit, I'd replace it with a new one.