94 XFI fuel guage not working

Hi, my fuel guage stopped working, it just stays on empty, no sign of moving when the ignition is turned on and off. Does anyone know what the voltages should be or have a good system for problem solving this to locate where the problem is. Thanks

All of the following information is for a '98 Metro, wire colors, etc, may very well be wrong. The general idea is the same across the entire 12 years though.

At the instrument cluster, connector C3 (13 cavities, white connector) pin 11 carries 12V going to the fuel gauge only pin 10 carries a ground originating at G104 (the main ground point on the back of the intake manifold, under the throttle body, and pin 9 carries the fuel level signal which is a variable ground.

The fuel tank sending unit gets its ground from G400, an eyelet screwed to the body back by the tail lights somewhere. This ground goes through the in tank sensor, which is basically a volume control, then travels up front to the gauge. Under the rear seat is a connector which has two black wires connected to the G400 ground, a pink wire coming from the fuel pump relay, should be 12V when the fuel pump is commanded on, and a YEL/RED wire which is the sending unit connection.

When the tank is full, the sending unit resistance is at 0 ohms, so the full ground from G400 is sent up to the gauge. When it is empty, the resistance in the sending unit is 130Ω. If you jumper across from the ground wires to the fuel gauge signal (YEL/RED) on the car side of that connector, the gauge should go to full. Check all the voltages at that connector first though, if you get across the wrong ones, you could trash something, you don't want to short the fuel pump feed, and you don't want to send the fuel pump 12V up front into the gauge.

My bet is on the ground at the rear bulkhead.

My bet is on the ground at the rear bulkhead.


Maybe not, now I'm thinking that the fuel pump wouldn't run if that ground was bad. It still needs to be checked as one of the simpler possibilities

.

Thats a big help. If I can get to it over the weekend will start by checking voltage and continuity and see. My guess is an interuption of current on the hot side since there is no movement at all in fuel gauge, and it stopped working all of a sudden and never came back. Im hoping to isolate the problem before I dig in.

Thanks for the help. On the fourth check I found the sending unit connector plug under the back seat was not making contact properly. Cleaned and pressed it together lightly. Its working like new now.