Think of it this way... The sensor at the tank runs across a coil. As the fuel level changes, the sensor slides up and down the coil. Over the years the winds of the coil start to wear through. As the fuel level goes up and down now, it loses contact as it goes over winds that are no longer connected like before. The level goes up and down, but the gauge no longer receives a complete, smooth signal.
This is why the gauge doesn't just slump and read empty all the time. When mine first started to go, it showed full, but as it got closer to half a tank it would drop down to almost empty for the last 100 miles.
Bottom line, when the gauge starts to lose connectivity, replace the tank sensor.
Last edited by Billjohn; 10-01-2008 at 10:19 PM.