Land Rover Repair: freelander fuel pump fault?, fuel level gauge, gauge pointer

Question
I recently got a freelander in the garage that was not starting changed fuel pump started ok after that however customer brought car back saying that fuel guage was reading empty when full and full when empty i have reversed the wires at sender unit and fitted second hand dash would be grateful if you could shine some light on this for me thanks chris guthrie r and j autos

Answer
Hi Chris,

did you test fuel pump before install?  Was it a new pump or salvage?

Here's some tech info:

Fuel Level Gauge
The fuel level gauge pointer indicates the current fuel level in the fuel tank. The fuel level gauge pointer returns to the empty position when the ignition is switched off.

The gauge is operated by an output from the fuel gauge to the fuel tank sender which is integral with the fuel pump.  
The sender is a float operated rotary potentiometer which provides a variable resistance to earth for the output from the gauge. Movement of the sender unit float arm varies the electrical resistance across the sender unit, so the voltage of the control signal and the resultant deflection of the gauge pointer are directly related to the level of fuel in the tank.

When the sender float is at its lowest point, indicating an empty fuel tank, the resistance to earth is at its greatest. The measured resistance is processed by the instrument pack to implement an anti-slosh function. This monitors the signal and updates the fuel gauge pointer position at regular intervals. This prevents constant needle movement caused by fuel movement in the tank due to cornering or braking.

A warning lamp is located in the face of the fuel gauge and illuminates when the fuel level is at or below 2.2 gallons (10 litres).

The fuel level sender signal is converted into a CAN message by the instrument pack as a direct interpretation of the fuel tank contents in litres. The ECM uses the CAN message to suspend OBD misfire detection when the fuel level is below 15% capacity.

Sender Unit Resistance (Ohms) -  Nominal Gauge Reading
503 - Empty
413 - Low fuel level illumination
302 - Half full
135 - Full


That's about all I know.  

Best of luck,

JohnMc