Fuel injection involves spraying or injecting fuel directly into the engine's intake manifold. Fuel injection, especially when it is electronically controlled, has several major advantages over carbureted systems. These include improved driveability under all conditions, improved fuel control and economy, decreased exhaust emissions, and an increase in engine efficiency and power.

Although fuel injection technology has been around since the 1920s, it wasn't until the 1980s that manufacturers began to replace carburetors with electronic fuel injection (EFI) systems. Many of the early EFI systems were throttle body injection (TBI) systems in which the fuel was injected above the throttle plate. Engines equipped with TBI have gradually become equipped with port fuel injection (PFI), which had injectors located in the intake ports of the cylinders. Since the 1995 model year, all new cars are equipped with EFI systems.

Diesel engines, for quite some time, have been equipped with fuel injection systems. The two basic differences between gasoline injection and diesel injection are: diesel fuel is injected directly into the cylinders, and diesel fuel injection systems are operated mechanically rather than electronically. Although late-model diesel systems use electronic fuel controls, the fuel injection system is a mechanical system that is controlled mechanically.