Prior to 1990, car engines were still built with carburetors as the means of supplying fuel to the combustion chamber, but after that all vehicles were instead equipped with fuel injection systems that are able to provide a more precise amount of fuel. This not only allows vehicles to be more fuel efficient, but it lowers emissions and improves performance as well.

The fuel injection system has been around since the 1950s, but electronic systems were not widely used until the 1980s.

Carburetors slowly began to be replaced as vehicle engine designs grew more complicated. At first, throttle body fuel injection systems replaced the old mechanics because they were able to be fitted to the engine in nearly the same way as carburetors without needing to make drastic design changes to the engine block. Throttle body systems involved single-point delivery, but as engines began to evolve, so did the fuel injection systems.

Most modern vehicles are equipped with multi-port fuel injection systems that deliver fuel to each individual cylinder, and they are aimed at the intake valves to allow for faster response times and more accurate fuel usage.

When you step on the gas pedal, the throttle valve opens up to allow air into the engine. The engine control unit (ECU) registers this action and signals the fuel injection system to increase the fuel rate as soon as the valve opens. This reduces the chance of engine hesitation that can otherwise be caused by an imbalance of air and fuel in the cylinders.

Combustion depends of a very precise ratio this mixture to function properly, and there are sensors that monitor the amount of air getting into the engine as well. The amount of fuel being delivered to the engine at any given moment is called the pulse width. The ECU uses this information along with the signals of the throttle valve and information from a number of other sensors to ensure that the amount of fuel correctly matches the amount of air,ensuring a proper response.

Pressurized fuel is sent from the fuel pump to the injector through the fuel rail, which then sprays it into the cylinder through a special nozzle that atomizes the gasoline. This way, it burns easily and uniformly for the best possible engine performance.