Fuel Gauge Reads "Empty"

[StephenJ]

Though a faulty gauge is not altogether urgent, my wife thought it would be good to have it working before our trip to the coast next week.

Have just abount finished restoring Zoey (our 76 280Z). When I purchased her, the gauge would work periodically. Now, it just stays all the way to the left. Am looking for help on how to diagnose the issue. Here is what I have done:

1. Replace the fuel sending unit with a new OEM unit. (no help)

2. Removed the gauge and inspected the connections...and also cleaned the points.

3. Connected a 9-volt battery (+ to yellow and - to black). The needle moved slowly to the "E", but not any further. I thought that perhaps that was good...and that there simply was not enough amperage to move it further.

4. Reconnected the gauge and turned key to "On"...moved just a smidge...but not even to the "E".

5. Disconnected the connector at the fuel sender and jumped the black to the yellow wire. Barely to the "E".

5. I get a strong buzz on my craftsman volt/ohm multimeter when testing for continuity from the black ground wire to the frame.

6. Not sure this would be accurate, but checked for voltage on the yellow wire at both the meter and at the sensor connector...there is NO voltage.

7. Checked the fuses...all are good.

8. Spinkled mojo dust and rattled the chicken bones...no help.

Any thoughts out there in how to test the gauge? Can I hook up 12vdc to the yellow and ground the black wire...or will that blow the thing? Or should there be voltage at the yellow wire? Looking at the FSM, I see no voltage going there.

All other gauges work...except the clock (of course).

[SteveJ]

I was playing with the fuel gauge in my car recently. I determined it was time to replace it, though. Fortunately for me, Dave Irwin, aka Zs-ondabrain, was very generous and sent me his old gauge that functioned perfectly.

Anyway, from my analysis during troubleshooting the old gauge, here is how I think it works:

1. Voltage comes in to the right side of the gauge (as you're facing it). It goes through the windings and splits in two. One path goes back to ground, and the other path goes through the windings on the left side of the gauge. Thus acting like a voltage divider.

2. From the left side of the gauge, the circuit goes out the yellow wire and back to the sender. The sender is just a resistor that affects the current flow through the gauge.

3. The electromagnets formed by the windings will pull the two parts of the gauge toward each other. Since the right side is fixed and the les, ft is not, the left windings move toward the right windings and allow the needle to move. (While you may know this already, I thought it might help others who have trouble with their fuel gauges.)

You should have had good deflection on the gauge with the 9V battery provided the battery was at its full charge. While you might have issues with corrosion elsewhere in the circuit, my partially educated guess is that your fuel gauge is ready to be refurbished.

Possible sources for gauges include

1. Asking here if someone has a spare gauge. The core membership here is made up of a great bunch of guys.

2. Contact Zspecialties. They are in Washington state and are very reputable.

[StephenJ]

Thanks Steve. I imagine you are right to replace it. Would the proper test be to hook up a 9V battery to it with the positive going to green, neg going to black, and jump from yellow to black?

[SteveJ]

Actually, with the test you ran, the needle should have probably gone to Full. If you wanted to test the movement, you could use 2 latern batteries in series to power the gauge, connect the positive to the green, the negative to black and wire a potentiometer to the yellow with the other side going to the battery negative. Then you can alter the resistance of the potentiometer and watch for movement on the gauge.