Port Fuel Injection (PFI), also known as Port-Injected Fuel Injection or simply Port Injection, is a fuel injection system in which fuel is sprayed into the intake ports just before the intake valve rather than directly into the combustion chamber. This setup provides improved fuel atomization and air-fuel mixture, which enhances combustion efficiency and engine performance. PFI is a step up from throttle body injection and is simpler and less expensive than direct injection systems, making it a popular choice in many vehicles.
In a PFI system, each cylinder has its own fuel injector located in the intake port:
Fuel Injection in Intake Port: Fuel is sprayed into each intake port right before the intake valve, where it mixes with incoming air.
Air-Fuel Mixture Formation: The fuel mixes with air in the intake port, forming a uniform air-fuel mixture. When the intake valve opens, this mixture is drawn into the cylinder.
Electronic Control: The Engine Control Unit (ECU) precisely controls the timing and amount of fuel injected based on data from various sensors to optimize fuel delivery and combustion.
Fuel Injectors: Each cylinder has its own injector positioned in the intake port, which delivers fuel in a fine spray.
Fuel Pump and Fuel Pressure Regulator: The fuel pump supplies fuel at a regulated pressure to the injectors.
Engine Control Unit (ECU): The ECU controls the fuel injection timing and duration based on sensor inputs, ensuring efficient fuel use.
Sensors: Includes sensors such as oxygen sensors, throttle position sensors, and intake manifold pressure sensors, which relay real-time data to the ECU to adjust fuel delivery.
Good Fuel Atomization: Fuel is atomized in the intake port, allowing for a uniform air-fuel mixture, which enhances combustion efficiency.
Lower Carbon Build-Up: Unlike direct injection, fuel in a PFI system passes over the intake valves, helping to wash away carbon deposits, which reduces maintenance.
Less Sensitive to Fuel Quality: PFI systems are less prone to issues caused by lower-quality fuel compared to direct injection, as the fuel is not injected at extreme pressures.
Cost-Effective: PFI systems are generally less complex and less costly to manufacture and maintain than direct injection systems.
Less Precise than Direct Injection: Since fuel is injected in the intake port rather than the combustion chamber, PFI cannot control the air-fuel mixture as precisely, which can slightly reduce efficiency and performance.
Lower Power Output: Direct injection can achieve higher power and fuel efficiency by delivering fuel directly into the combustion chamber, which PFI cannot match.
Emissions: Though PFI is relatively efficient, it doesn’t have the same emissions reduction capabilities as direct injection, especially under high engine loads.
PFI is widely used in a variety of vehicles due to its balance of cost-effectiveness, efficiency, and lower maintenance needs. Many modern vehicles use PFI systems, either alone or in combination with direct injection (as in dual-injection systems) to take advantage of the strengths of each technology. PFI remains common in small- to medium-sized engines, motorcycles, and other applications where fuel efficiency and simplicity are prioritized over maximum performance.