The ECU has the ability to evaluate the results of its calculations and commands, remember the modes of recent operation and act in accordance with them. «self-learning» or ECU adaptation is a continuous process, but the corresponding settings are stored in the RAM of the electronic unit and, therefore, until the first power off of the ECU.
Fuel is supplied by 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 the engine start mode. The ECU turns on the injectors in series. Each of the nozzles is activated every 720°of crankshaft rotation. This method allows you to more accurately dose the fuel into the cylinders and reduce the level of toxicity of exhaust gases.
The amount of fuel supplied is determined by the state of the engine, i.e. its mode of operation. These modes are provided by the ECU and are described below.
When the crankshaft of the engine begins to scroll with the starter, the first pulse from the crankshaft position sensor causes a pulse from the ECU to turn on all the injectors at once, which allows you to accelerate the start of the engine.
Initial fuel injection occurs each time the engine is started. The duration of the injection pulse 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 relay for the electric fuel pump, 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 starts to crank, 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 on warmed up - less.
Acceleration rich mode
The ECU monitors sudden changes in throttle position (throttle position sensor signal), as well as the signal from the mass air flow sensor and provides an additional amount of fuel by increasing the duration of the injection pulse. Acceleration rich mode is only used for transient fuel control (when moving the throttle).
Fuel cut-off mode during engine braking
When braking with the engine in gear and clutch engaged, the ECU may completely shut off the fuel injection pulses for short periods of time. Turning off and on the fuel supply in this mode occurs when certain conditions are created for the coolant temperature, crankshaft speed, vehicle speed and throttle opening angle.
Supply voltage compensation
If the supply voltage drops, the ignition system may produce a weak spark, and mechanical movement «discoveries» injectors may take longer. The ECU compensates for this by increasing the energy storage time in the ignition coils and the duration of the injection pulse.
Accordingly, when the battery voltage increases (or voltage in the vehicle's on-board network) The ECU reduces the energy storage time in the ignition coils and the duration of the injection.
Fuel cut mode
When the engine is stopped (off ignition) fuel is not supplied by the nozzle, thus eliminating spontaneous ignition of the mixture in an overheated engine. In addition, pulses to open the injectors are not given if the ECU does not receive «support» pulses from the crankshaft position sensor, i.e. this means the engine is not running.
The fuel supply is also turned off when the maximum permissible engine speed is exceeded, equal to 6200 min-1, to protect the engine from operating at unacceptably high speeds.