The fuel pump, located in the fuel tank, delivers fuel to the fuel rail through the fuel filter. The fuel pressure in the system is controlled by the pressure regulator. It allows excess fuel to return to the fuel tank when the pressure in the system is exceeded. The fuel rail is a reservoir for the injectors, which inject fuel into the intake ports of the engine cylinders. The engine uses a distributed fuel injection system, in which the injectors inject fuel independently of each other. The unit controls the operation of the injectors by changing the pulse duration - the length of time during which the injector is open - to ensure the supply of a richer or leaner combustible mixture.
The air passes through the air filter, air flow meter and throttle valve to the intake ports of the cylinders. Based on the information from the air flow meter and sensors, the control unit adjusts the time and amount of fuel injected in accordance with the metered amount of air and the engine speed. The longer the injector is open, the more fuel is injected.
Additional sensors transmit information to the control unit about the temperature of the coolant and the air entering the engine, and on models with a catalytic converter – about the oxygen content in the exhaust gases.
The activated carbon filter prevents harmful fuel vapors from entering the atmosphere from the fuel tank. Fuel vapors accumulate in a canister with activated carbon - an adsorber and are burned in the engine cylinders when the engine is running.
A memory device in the control unit recognizes the malfunction that has occurred and records it. If an important sensor fails, the control unit switches to an emergency program so that the engine continues to operate, albeit with less efficiency.
Ignition system creates a spark discharge in each engine cylinder at a certain moment, which ignites the compressed combustible mixture.
(The original publication in its entirety is posted on the website: AUDImanual)