The fuel control unit improves the performance of the engine, enabling it to work as efficiently as possible while increasing the life of the engine. 

The engine needs the correct amount of air and fuel flowing through it in order for the fuel to burn in the cylinders and for the engine to ignite or spark at the right time. If the ignition sparks at the wrong time, there will be less power in the engine and it will try to make up for this by using more fuel, significantly reducing fuel efficiency, which in turn increases the car's CO2 emissions. If combustion occurs too soon this can also cause significant damage to various engine components.

The car's ECU (Engine Control Unit) uses data provided by clever sensors mounted on the engine which measure factors such as air pressure; the speed the engine is rotating; engine temperature; acceleration position; the temperature of the air; and the level of fuel flowing into the engine to make vital adjustments to ensure the right amount of air and fuel mix is entering the engine at the point which the ignition sparks. The fuel control unit is a system that provides fuel pumping, metering, and fuel filtration. The fuel control unit measures the exact amount of fuel flowing into the engine, and in conjunction with the ECU, adjusts various valves to either increase or decrease the flow of fuel based on the demands of the engine. The fuel control unit usually includes the fuel sender unit and fuel gauge. Usually attached to the fuel pump, and normally located in the fuel tank, the fuel sender unit measures the level of fuel in the tank, usually with the aid of a float and a clever resistor  type sensor. The fuel level data is sent to the car's fuel gauge, normally located on the dash board. The fuel gauge shows the level of fuel in the tank. As the fuel is used, the floats lower in the fuel sender unit and the fuel gauge reflects this by slowly moving down. This enables the driver to see how much fuel is left in the tank. The driver would use this information to fill the car up with fuel as and when required. It helps the driver to make sure the fuel levels don't get too low. Worse case scenario is running out of fuel. Running out of fuel can damage  the engine. Running a car on low levels of fuel can also be harmful to engine components and the fuel system, including the fuel filter and fuel pump.

Problems with the fuel system should be fixed as soon as possible. If the fuel control unit is faulty this can affect the entire fuel system and can lead to engine problems. A faulty fuel control unit may affect the accuracy of the information displayed on the fuel gauge and could lead to the car running out of fuel. When replacing the fuel control unit it's wise to make sure the replacement part is compatible with your car. Specifically manufactured for the make and model of your vehicle, a good quality fuel control unit provides superior performance and long working life.