Port Injection
A fuel delivery system design where fuel is sprayed into the intake port or manifold, mixing with air before entering the cylinder.
Port Fuel Injection (PFI) is a common fuel system design where fuel injectors are located in the intake manifold runners, just outside the intake valves. The injector sprays fuel onto the back of the intake valve, where it mixes with incoming air before being drawn into the combustion chamber when the valve opens.
PFI operates at relatively low pressures (typically 40 to 60 PSI) compared to direct injection systems. A key advantage of port injection is that the fuel spray constantly bathes the backs of the intake valves with gasoline and cleaning additives. This prevents carbon deposits from accumulating on the valve stems, keeping the intake tract clean over hundreds of thousands of miles.
While highly reliable and simple, port injection is slightly less efficient than direct injection because some fuel droplets cling to the intake walls, and it does not provide the same in-cylinder cooling effect. Some modern engines use a 'dual-injection' system, combining both port and direct injectors to capture the efficiency of GDI and the valve-cleaning benefits of PFI.