The ECU has the ability to evaluate the results of its calculations and commands, remember recent operating modes and act in accordance with them. "Self-learning" or adaptation of the ECU is a continuous process, but the corresponding settings are stored in the RAM of the electronic unit and, therefore, until the first power outage of the ECU.
Fuel is supplied using one of two different methods: synchronous, i.e. at a certain position of the crankshaft, or asynchronous, i.e. independently or without synchronization with the rotation of the crankshaft. Synchronous fuel injection is the most commonly used method. Asynchronous fuel injection is used mainly in engine starting mode. The ECU switches on the injectors sequentially. Each of the injectors is switched on every 720° of crankshaft rotation. This method allows for more precise dosing of fuel between cylinders and a reduction in the level of toxicity of exhaust gases.
The amount of fuel supplied is determined by the state of the engine, i.e. its operating mode. These modes are provided by the ECU and are described below.
When the engine crankshaft begins to rotate with the starter, the first pulse from the crankshaft position sensor causes a pulse from the ECU to turn on all injectors at once, which allows the engine to start faster.
The initial injection of fuel occurs each time the engine is started. The injection pulse duration depends on the temperature. On a cold engine, the injection pulse is longer to increase the amount of fuel; on a warm engine, the pulse duration is reduced. After the initial injection, the ECU switches to the appropriate injector control mode.
Start mode
When the ignition is turned on, the ECU turns on the electric fuel pump relay, which creates pressure in the fuel supply line to the fuel rail.
The ECU checks the signal from the coolant temperature sensor and determines the amount of fuel and air required for starting.
When the engine crankshaft begins to turn, the ECU generates a phased pulse to turn on the injectors, the duration of which depends on the signals from the coolant temperature sensor. On a cold engine the pulse duration is longer (to increase the amount of fuel supplied), and when warmed up - less.
Enrichment mode during acceleration
The ECU monitors sudden changes in the throttle position (by signal from the throttle position sensor), as well as the signal from the mass air flow sensor and ensures the supply of an additional amount of fuel by increasing the duration of the injection pulse. The enrichment mode during acceleration is used only for fuel control in transient conditions (when moving the throttle valve).
Fuel shut-off mode during engine braking
During engine braking with the gear and clutch engaged, the ECU may completely disable fuel injection pulses for short periods of time. The fuel supply is switched on and off in this mode when certain conditions are created for the coolant temperature, crankshaft speed, vehicle speed and throttle opening angle.
Supply voltage compensation
When the supply voltage drops, the ignition system may produce a weak spark, and the mechanical movement of "opening" the injector may take longer. The ECU compensates for this by increasing the energy accumulation time in the ignition coils and the injection pulse duration.
Accordingly, when the battery voltage increases (or voltage in the vehicle's on-board network) The ECU reduces the energy accumulation time in the ignition coils and the injection duration.
Fuel Shut-Off Mode
When the engine stops (ignition off) the fuel is not supplied by the injector, thus eliminating spontaneous ignition of the mixture in an overheated engine. In addition, pulses to open the injectors are not sent if the ECU does not receive "reference" pulses from the crankshaft position sensor, i.e. this means that the engine is not running.
The fuel supply is also cut off when the maximum permissible engine crankshaft speed of 6200 min⁻¹ is exceeded to protect the engine from running at unacceptably high speeds.