Whether your car has a carburettor or a fuel injection system, it will have a fuel pumping system of some sort to send fuel to the engine through a hose or line. The amount of pressure under which the fuel is delivered by the pump will depend on which system your engine uses; a carburettor system requires lower pressure whereas a fuel injection system requires higher pressure. The fuel pump sending unit is a clever device for measuring the fuel level in the fuel tank and communicating this information to your dashboard via the fuel gauge. If the fuel drops below a designated level a foam float connected to a metal rod starts to descend. At the end of the rod a variable resistor makes contact with a wiper that is connected to the fuel gauge, conducting a certain amount of electrical current. The amount of resistance – ultimately depending on the position of the float – is what tells your dashboard indicator when the fuel level is getting low. A fully functioning fuel pump and sending unit combo will ensure that your engine does not suffer from fuel starvation, which would certainly affect the smooth running of your car.