Fuel Systems: EFI Engine Management

EFI operation	Modes of EFI	A mode of injection describes the timing and sequence of injecting fuel.
	Electronic fuel injection	EFI is now the most common fuel system, the injectors spray fuel into the air/intake ports for combustion inside the engine.
	Idle speed control systems	Idle speed control systems maintain a suitable idle speed to prevent stalling, when additional loads are placed on the engine.
	Feedback & looping	Feedback from the exhaust gas oxygen sensor is used to maintain closed loop control of the air-fuel mixture.
	Cold start systems	Cold start systems provide additional fuel during starting conditions, according to engine temperature.
	Air measurement	The vane-type airflow sensor measures the quantity of air flowing into the engine by deflecting a spring-loaded vane across a potentiometer. This provides a signal voltage to the ECU.
	Air-flow monitoring	Depending on the application, different kinds of sensors measure different properties of the air entering the engine, including its temperature, volume, density, and mass.
	Variable intake manifold system	Variable intake manifold systems vary the effective manifold pipe length, to extend the torque curve over a wider RPM range.
	Electrical functions	The ECU continuously receives information from sensors in the form of electrical signals, to determine injector pulse width.
	EFI wiring diagram	Identification of the sensors and their inputs allows easier identification of the wiring diagram for any given system.

Electronic control unit - ECU	EFI system ECU	The basic function of the ECU is to control the pulse width of the injector. In engine management systems, the ECU controls additional functions, such as idle speed, ignition timing, and fuel pump operation.
	Electronic control unit settings	The ECU corrects ignition timing to achieve the optimum setting for each operating condition.
	Engine speed limiting	An ECU can control engine speed limiting, the fuel pump, exhaust gas recirculation, idle speed control, a variable intake manifold, and the evaporative emission container.
	Malfunction indicator lamp	A check engine lamp or a data scanner can be used to indicate problems in the engine management system. A code indicates where the fault may be.

EFI sensors	Mass airflow sensor	Mass airflow sensors detect the mass of air entering the engine directly, using a hot wire, or a heated ceramic plate resistor.
	Manifold absolute pressure sensor	Manifold absolute pressure sensors measure changes in intake manifold pressure caused by changes in engine speed and load, and convert them into electrical signals.
	Air vortex sensor	The air vortex sensor uses whirlpools of air, produced by a vortex-generating rod, to measure the volume of air entering the engine. This is converted to an electrical signal that is transmitted to the ECU.
	Fuel system sensor	The fuel system sensor determines how much fuel the engine needs at that instant, then grounds the injection valve circuit, to open the solenoid-operated injectors. This information is relayed as electrical signals to the ECU.
	Temperature sensor	Temperature sensors relay information to the ECU on engine coolant and intake manifold temperature.
	Throttle position sensor	Throttle position sensors relay information to the ECU on throttle position, to allow adjustments to fuel settings, according to operating conditions.
	Exhaust gas oxygen sensor	Exhaust gas oxygen sensors monitor the oxygen content of the exhaust gas, and relay this information, by means of a voltage signal, to the control unit.
	Crank angle sensor	Crankshaft position and speed can be detected by inductive-type sensors which act as small alternators. The frequency of the pulse they transmit allows the ECU to detect engine speed.
	Hall effect voltage sensor	A Hall effect sensor provides voltage pulses that are generated by alternately shielding the sensor from a magnetic field, then exposing it. An ECU uses this signal to detect engine speed and control ignition timing.

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