I've got a 1988 Firebird, when the tank is full, the gauge only reads half full. Does anybody know what pin at the gauge cluster harness is for the fuel gauge? Also, what the resistance should be at full and empty? I'd like to determine if the gauge broken, or if the sender or wiring is at fault.

 

Here’s how to test the fuel gage.

Remove the sender wire going to the gage.

Tape the removed sender wire so it can’t short.

Use a potentiometer with a value of 90Ω or the closest you can find.

Connect one end the potentiometer to the gage from the location you removed the sender.

Connect the wiper of the potentiometer to ground.

Turn the key to RUN.

Slowly adjust the potentiometer from 0Ω to 90Ω.

If the gage is bad it will exhibit the problem you have.

If the gage is good it will display a smooth transition from one end of it’s range to the other.

Therefore the problem is with the sender or wiring going to it.

0Ω = Empty, 90Ω = Full

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Happy Racing!

 

Do you know where I could pick up a 90ohm potentiometer? Radioshack doesn't have one, I found a 100ohm pot online though.

For now I'll just test the sender directly, I would want to put the ohm meter between the sender wire and ground at the fuel pump harness correct? I'll fill up the tank, and check if it reads close to 90ohms.

 

A 100Ω potentiometer is fine for testing.

When you go past 90Ω it might peg, but you’ll know why it’s happening.

Also, with an ohmmeter, you can find where 90Ω is on the potentiometer and mark it.

Quote:

For now I'll just test the sender directly, I would want to put the ohm meter between the sender wire and ground at the fuel pump harness correct? I'll fill up the tank, and check if it reads close to 90ohms.

That’s true.

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Happy Racing!