Mazdaspeedfc3s

I bought this car is December and finally got it all cleaned up and on the road. The fuel gauge used to read about 3/8 full. Now its sitting right above the empty line. Ive added fuel with no change to the gauge. Where should I start? I searched the forum with no real luck.

DC5Daniel

iTrader: (10)

You can check both the gauge and the sending unit. The FSM has the procedure for this.

The high level overview is I would disconnect the sending unit and meter the resistance (it is just a variable resistor). The FSM will list what the expected values are for full, empty, and somewhere in between. You can then apply your own resistances to the gauge via the harness, but be careful. I use a lab grade resistor substitution box to sweep the gauges, but if you have a collection of different resistors you can probably make what you need.

The way these old gauges work is they rely on heat (generated by current) to bend a metal strip and move the needle (with the exception of the boost gauge). The gauges have no current limiting protection, and become permanently damaged when shorted or have too much current through them. This is why the oil pressure gauges are usually destroyed when people accidentally ground the broken connectors where the condensers used to connect.

Hopefully the gauge is still okay, but if not the cluster is easy to take apart and replace with gauge from a donor cluster. It is paired with the temp gauge, so make sure both gauges are working before buying.

Mazdaspeedfc3s

Great info. Thank you. I will start looking into it