This article covers disassembling and restoring the factory fuel level sender to a usable state. Most Fieros nowadays have highly inaccurate  senders, resulting in running out of gas at 1/4 to 1/2 tank. This repair typically gets the unit much closer to accurate.

For details on removing the tank from the car, see here:

How To - Replace A Fiero Fuel Pump

I did this repair on mine today, and now my gauge went from running out of gas at 1/2 tank, to actually reading almost right on.

First step, drop the tank and pull the sending unit. Process on doing so is covered elsewhere.

Now, check the resistance at the terminals connected to the Black and Purple wires. Or if yours is different just test the ground wire and whichever is connected to the float. Normal operation is 0ohms empty, 90ohms full.

Here is mine before the repair, with the float in the empty position I'm getting a reading of 40.6, nearly a half tank.

Remove these two Torx screws to get at the resistor, be careful not to lose the two springs:

Here is the resistor, you can see quite a bit of build up. Fortunately we are only really concerned with the leading edge, and the mount location.

Gently clean this leading edge, this is where the float mechanism slides against. I used a coarse sponge, very fine sandpaper may work as well.

Clean this plate as well, the spring needs to make good contact in this area:

Sand clean both ends of the upper spring, as well as the metal plate it contacts:

Re-assemble the resistor to the sending unit, ensuring the plate from the float is behind the resistor:

Re-test your sending unit in both the empty and full positions. I now get 7.6 empty and 107.6 full, this will work okay for now. I can adjust the gauge to compensate for the slightly high reading.

Re-install your sending unit into the tank and re-test. On mine, I had to bend the float arm up slightly, it appeared to be hitting the bottom. In fact, in the empty position it was below the bottom level of the pump.

Bending float arm:

Re-testing in tank:

My tank used to run out when the gauge read 1/2 , and filling the tank would result in the gauge pegging way off to the right. Now the gauge is nearly right-on. With the tank totally empty the needle is just above the empty mark, and filling the tank puts the needle just above full. This is the result of being high by 7.6ohms. Since its off by the same amount on both ends I'll just re-adjust the needle to be correct on empty.

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