Hi My C320 W203 runs out of fuel but the gauge shows quarter tank. When you switch the Key to 2nd position you can hear the pump run. I've inspected the piping between the pump and sender unit and all seems to be in order. Please assist with possible causes and or remedies

 

What is the quality of the petrol like there?.. could it be mixed with water? which has now settled at the bottom of the tank?..
I would suggest checking the contents of the tank when the engine stops running, and seeing if there is water in there, causing it to show on the gauge??..