Vehicles today use fuel injectors to mix fuel with air. Fuel injection has evolved over time.
Throttle Body Injection (TBI). TBI systems replaced carburetors. In a TBI system, a fuel injector is placed above the throttle body, supplying fuel to all the cylinders.
Port Fuel Injection (PFI). TBI systems were eventually replaced by PFI. In a PFI system, there is a fuel injector located near the intake port (before the intake valve) for each cylinder. PFI systems achieve greater precision over TBI systems by delivering equal amounts of fuel to each cylinder.
Gasoline Direct Injection (GDI). Today, GDI is gaining popularity. In a GDI system, each cylinder has a fuel injector that sprays a high-pressure fuel mist directly into the combustion chamber.