PortFuelInjection

Port fuel injection (PFI) is a method of delivering gasoline into the intake port of an internal combustion engine. In a PFI system, fuel is sprayed by one or more injectors into the intake port, upstream of the intake valve, where it mixes with incoming air before entering the combustion chamber.

Operation: Most engines using PFI employ one injector per cylinder (multi-point fuel injection, MPFI). The injectors are actuated by an engine control unit (ECU) that meters fuel according to signals from sensors such as mass air flow, oxygen, throttle position, and coolant temperature. The resulting air–fuel spray vaporizes as it enters the port and forms a combustible mixture that is drawn into the cylinder during the intake stroke. Some systems fire injectors sequentially in the intake cycle, while others use batch or group firing.

Variations and hardware: Earlier systems used a centralized throttle body injector; modern MPFI devices place injectors directly at each port for more precise control. Fuel delivery may be return-type, with a returned portion of excess fuel, or returnless, with a pump in the fuel tank and an inline regulator. In many vehicles, additional features such as idle control and auxiliary injectors may be present.

Advantages: Port injection provides improved air–fuel metering, smoother idle, better cold-start performance, and lower emissions compared with carburetors. It also allows finer control of fuel at part-throttle operation than older throttle body designs.

Disadvantages: Compared with direct injection, PFI generally offers lower high-end volumetric efficiency and can be susceptible to port deposits over time, which may require maintenance.

History: Port fuel injection became widespread in the 1980s, with MPFI standard in many passenger cars during the 1990s as electronics and sensors advanced.