Have a 86 1/2 Gt with the fuel gauge pegged past full. Pulled the fuel tank, cleaned the sender, check it with an ohm meter and it is reading correctly. What is the next step? Thank you in advance.

If the fuel gauge shows FULL when the tank is not full, disconnect the fuel sender connector (in the engine compartment), turn the key to RUN (engine off) and in the chassis half of the connector jump the pin with the black wire to the pin with the pink wire. If the fuel gage now reads empty, the wiring between the instrument panel and the engine bay is good. If it does not, then the fuel sender is malfunctioning or the wires between the connector and the sender are faulty.

quote Originally posted by Bloozberry: If the fuel gauge shows FULL when the tank is not full, disconnect the fuel sender connector (in the engine compartment), turn the key to RUN (engine off) and in the chassis half of the connector jump the pin with the black wire to the pin with the pink wire. If the fuel gage now reads empty, the wiring between the instrument panel and the engine bay is good. If it does not, then the fuel sender is malfunctioning or the wires between the connector and the sender are faulty.

upon jumping the pink and black pins on the chasis, the gauge goes to empty. So I would assume, per the above that the dash gauge and the wiring to the chasis connector is ok and that the problem is the wiring to the sender or the sender itself per your above post.

That's correct. To to isolate the problem even further, use a multimeter set to the 200 ohm range and measure the resistance between the pin with the black wire and the pin with the pink wire on the gas tank side of the harness. Depending on how full the tank is, you should get 90 ohms (full tank) or zero ohms (empty tank) or somewhere in between. If you get way more than 90 ohms then the sender is the wrong one. If you get infinite ohms then either the pink wire or the black wire is broken, or the circuit inside the sender is faulty.

The white wire that connects the sender to the top of the unit is where the problem is at. Specifically, the sender that the white wire connects to. In the process of cleaning it. The gauge is moving from couple bars away from "E" to Full. Progress. Thank you for your help with this.

I am trying to diagnose a very similar problem.

I recently replaced the sender in the tank, with the "newer technology" one from the Fiero Store for $205. Turned out to be a semi waste of money, as that is not my problem, as the gauge still reads below Empty no matter how much fuel is in it. Sometimes it is in other random locations on the gauge.

Anyhow...

quote Originally posted by Bloozberry: disconnect the fuel sender connector (in the engine compartment),

where exactly in the engine compartment? I have looked and can not see the connecter you are referring to. I have the relays under the grate behind the driver, the main harness going to the ECM, and a few others. None of them seem to have a pink wire on them.

[This message has been edited by JohnWPB (edited 09-04-2014).]

quote Originally posted by JohnWPB: I am trying to diagnose a very similar problem. I recently replaced the sender in the tank, with the "newer technology" one from the Fiero Store for $205. Turned out to be a semi waste of money, as that is not my problem, as the gauge still reads below Empty no matter how much fuel is in it. Sometimes it is in other random locations on the gauge. Anyhow... where exactly in the engine compartment? I have looked and can not see the connecter you are referring to. I have the relays under the grate behind the driver, the main harness going to the ECM, and a few others. None of them seem to have a pink wire on them.

The plug for the fuel sender is roughly in the center of the "firewall" about 1/2 ways down from the back window.

I personally would verify the gauge by inserting a 100Ω pot at the gauge side connector, adjust it and watch the needle move. At roughly 90Ω that gauge should show full. Or use a larger one pot, set it to 90, connect and adjust "down".

I recently had a gauge problem - would work "correctly" unplugged and shorted, but the actual "scale" was off. Turns out the reference side coil of the gauge had changed value (I have a meter that will measure coils).

quote Originally posted by Mickey_Moose: The plug for the fuel sender is roughly in the center of the "firewall" about 1/2 ways down from the back window. I personally would verify the gauge by inserting a 100Ω pot at the gauge side connector, adjust it and watch the needle move. At roughly 90Ω that gauge should show full. Or use a larger one pot, set it to 90, connect and adjust "down". I recently had a gauge problem - would work "correctly" unplugged and shorted, but the actual "scale" was off. Turns out the reference side coil of the gauge had changed value (I have a meter that will measure coils).

Thanks I will look for the plug there. As for trying a potentiometer, I do not have access to one, and honestly, not too much of an idea how to do it actually I will try with the stuff in the previous posts in this thread to start, and hopefully that can diagnose it, if not I will move on to using pot

quote Originally posted by JohnWPB: where exactly in the engine compartment? I have looked and can not see the connecter you are referring to.

Ahhh! Thank you. In the seconf post where you say "in the engine compartment" was just a little vague

Much appreciated, now to start testing....