EFI systems employ injectors to spray the fuel into the intake system. An electronic control unit processes data received from various sensors to optimize the air fuel mixture at any given moment by adjusting the amount of fuel injected.
EFI is a pressurised, indirect-injection system with solenoid-operated injectors. In multi-point injection, one injector is in each intake manifold runner. Single-point injection uses one or two injectors in a carburetor-like throttle-body.
The design of the intake system determines how much air can be drawn into a cylinder at any given engine RPM. EFI can achieve uniform distribution of the air delivered to the cylinders.
The amount of air entering the engine must be measured, so that the amount of fuel injected into it forms a mixture to suit the engine operating conditions at that time.
For any injection duration, if fuel is held at constant pressure, then, as manifold pressure varies, so does the amount of fuel delivered. That means fuel pressure must be held constant above manifold pressure.
In multi-point injection, the injectors can all be triggered simultaneously, twice per cycle. In a throttle-body system, the central injector is normally triggered on each ignition pulse. With two injectors, alternate triggering may be used.
Adaptive learning is a form of feedback that lets fuel settings change as components age. The ECU memorizes its fuel settings for different operating conditions, and stores them for future use.
