Crazy Gauge Options

[Prime91]

Model:998cc City E
Year:1989
Hey guys. When I fill up my tank, the fuel gauge reads full, as you would expect, but when I've used less than a quarter of the tank it drops down to empty, and stays there until I fill up again. Every now and then the gauge will show a reading though, a random reading at random times from what I've worked out.

I've changed the clocks from 3-clock to a centre speedo with the fuel gauge built in, so could this be a wiring fault on my part? It seems odd to me for it to be wiring as it works fine and then drops to empty after such a small amount of time.

Any thoughts would be most appreciated!

[POWER5LAVE]

i know this isn't an answer but mine does exactly the same. ive tryed changing the clocks and that doesnt fix it. i even changed the tanks once and still no joy

any help on this would be much appreiated

[MiniMan65]

I had the same problem on mine after a switch over and I thought it was the gauges but I fitted a new sender in the tank and it was working perfectly. Might want to try that, take the old one out the tank first and move the floater up and down slowly and see what the gauge does.

[dklawson]

The symptoms you are describing are consistent with what MiniMan65 found to be his sending unit.

To elaborate a bit, the sending unit is a variable resistor. In the Mini it is made up of a coiled piece of resistance wire. One end of that coiled wire is connected to earth. An electrically conductive "wiper" slides along the coil as the float arm moves up and down inside the tank. The wiper is connected to the fuel gauge via the green/black wire on the sending unit.

Occasionally (for some reason) the resistance coil will fail... breaking somewhere along its length. Your gas gauge will work OK when full but eventually the wiper passes over the break in the windings and the gauge looses its resistance path to earth and the reading goes to "empty".

Changing the sending unit should fix the problem. The quick test is to wait until the failure happens and the gauge is showing empty when you know the tank still has gas in it. With the ignition switch in the run position, use a paperclip to jumper across the two terminals on the sending unit (leave the wires connected). Have a friend watch the gauge. If it goes to full with the paperclip held to the terminals (and returns to empty when the clip is removed) you have confirmed the problem is the sender.

[Prime91]

The symptoms you are describing are consistent with what MiniMan65 found to be his sending unit.

To elaborate a bit, the sending unit is a variable resistor. In the Mini it is made up of a coiled piece of resistance wire. One end of that coiled wire is connected to earth. An electrically conductive "wiper" slides along the coil as the float arm moves up and down inside the tank. The wiper is connected to the fuel gauge via the green/black wire on the sending unit.

Occasionally (for some reason) the resistance coil will fail... breaking somewhere along its length. Your gas gauge will work OK when full but eventually the wiper passes over the break in the windings and the gauge looses its resistance path to earth and the reading goes to "empty".

Changing the sending unit should fix the problem. The quick test is to wait until the failure happens and the gauge is showing empty when you know the tank still has gas in it. With the ignition switch in the run position, use a paperclip to jumper across the two terminals on the sending unit (leave the wires connected). Have a friend watch the gauge. If it goes to full with the paperclip held to the terminals (and returns to empty when the clip is removed) you have confirmed the problem is the sender.

Thank you very much for this advice dklawson, I experimented with the paper clip and ordered a new sender, which is working perfectly!

Thanks again.