A car's fuel system stores fuel and supplies it to the engine by mixing the fuel with air, in addition to atomizing and vaporizing it, before it's compressed in the engine cylinder and ignited to produce energy. Different cars utilize different kinds of fuel systems, but fuel systems always supply fuel to the combustion chamber and regulate the amount of fuel supplied in relation to the amount of air.
After the fuel pump draws fuel from the tank, it moves through the fuel lines and arrives to the fuel injectors via a fuel filter. As the fuel reaches the fuel injectors, the processes of atomization and the determination of its spray pattern prepares it for complete combustion. Atomization is the result of the injection pressure; the diameter of the holes in the injector influence this process. The spacing, angle and number of holes in the injector tip determine the fuel's spray pattern.
Fuel pressure is regulated differently depending on whether the car's fuel system is return or returnless. A return system uses a fuel-pressure regulator, whereas a returnless system relies on the powertrain control module to control fuel delivery. Signs that a car's fuel system is not working properly include trouble starting the engine, slow acceleration, stalling, rough idling and lower fuel efficiency.