The conventional fuel delivery method that sprays gasoline into the intake port before the intake valve, allowing fuel and air to mix before entering the combustion chamber.
Port injection (also called multi-point fuel injection or MPFI) delivers fuel through injectors positioned in the intake port, upstream of the intake valve. The fuel mixes with incoming air in the port before the intake valve opens, entering the combustion chamber as a premixed charge. Port injection has been the standard automobile fuel delivery method since the widespread replacement of carburetors in the 1980s and 1990s.
Port injection's key advantage over earlier systems is that the fuel spray actively washes the back of the intake valves, preventing carbon buildup. Intake valves on port-injected engines remain clean for very high mileages, which is one reason older naturally aspirated Honda B-series, Toyota 2JZ, and similar port-injected engines can accumulate 200,000 miles with good maintenance.
Modern performance applications often combine port injection with direct injection. Ford's Coyote 5.0 (2018 onward), Toyota's 2GR-FKS, and several others use both: direct injection handles high-load fueling for efficiency and power, while port injectors keep the intake valves clean and supplement fueling during transients. This dual or combined injection approach is increasingly the industry standard for premium engines, capturing the efficiency advantages of direct injection while maintaining the valve-cleaning benefit of port injection.