The ECU has the ability to evaluate the results of its calculations and commands, as well as remember the experience of recent work and act in accordance with it. "self-learning" The ECU is a continuous process that continues throughout the life of the vehicle.
Typically, one pulse is applied to the injector per one reference pulse of the crankshaft position sensor. Fuel is supplied either synchronously with the reference pulses or asynchronously, i.e. without coincidence with them in time. Synchronous fuel injection is the most commonly used fuel delivery method. Asynchronous fuel injection is used when additional fuel is needed when the throttle is suddenly opened, as indicated by the throttle position sensor. This injection of fuel is similar to the delivery of fuel by the accelerator pump of a carburetor when the throttle is suddenly opened.
Regardless of the injection method, the fuel supply 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.
Engine start mode
When the ignition is turned on, the ECU turns on the electric fuel pump relay for 2 seconds, and it creates pressure in the fuel supply line to the central injection unit. The ECU takes into account readings from the coolant temperature and throttle position sensors and determines the correct air/fuel ratio for starting.
After the start of rotation of the crankshaft, the ECU will operate in the starting mode until the speed exceeds 420 rpm, otherwise it may switch to the mode "purge" engine. The duration of each pulse per injector at start-up is 4–6 ms, depending on the temperature of the coolant and the position of the throttle valve.
Engine purge mode
If the engine "filled with fuel", it can be started by fully opening the throttle while cranking the crankshaft. The ECU in this mode gives pulses to the injector corresponding to the air / fuel ratio of 26: 1 (pulse duration approx. 2 ms), What "cleanses" filled engine. The ECU maintains the specified pulse width as long as the engine speed is below 420 rpm, and the throttle position sensor indicates that it is almost fully open (over 85%).
If the throttle is held almost wide open when attempting a normal start "not flooded" engine, the engine may not start, as an air/fuel ratio of 26:1 may not be sufficient to start an unfilled engine, especially if it is cold.
Open loop mode after start (no feedback)
After starting the engine (when the revolutions are more than 420 rpm) The ECU will control the fuel supply system in mode "open cycle". In this mode, the ECU ignores the signal from the oxygen sensor and calculates the duration of the pulse to the injector based on the signals from the crankshaft position sensor (speed information), absolute air pressure sensor, coolant temperature sensor and throttle position sensor.
In open cycle mode, the calculated injection pulse width may give an air/fuel ratio other than 14.7:1. An example would be when the engine is cold, as a rich mixture is required for good driving performance.
The system will remain in open loop mode until all of the following conditions are met:
- the oxygen sensor signal changes, indicating that it is warm enough for normal operation;
- coolant temperature is more than 32°C;
- The engine has been running for a certain period of time since it was started.
The time can vary from 6 seconds to 5 minutes depending on the temperature of the coolant at the time of starting the engine. If the temperature was below 18°C, the period is 5 minutes. If the temperature was above 75°C, the delay is 6 seconds.
Closed loop mode after start (with feedback)
In closed loop mode, the ECU first calculates the pulse width per injector based on signals from the same sensors as in open loop mode. The difference is that in closed loop mode, the ECU still uses the signal from the oxygen sensor to correct and fine-tune the calculated pulse in order to accurately maintain the air / fuel ratio at 14.6... 14.7: 1. This allows the catalytic converter to operate at maximum efficiency.
Acceleration rich mode
The ECU monitors sudden changes in throttle position (by throttle position sensor) and the pressure in the intake pipe (by absolute pressure sensor) and ensures the supply of an additional amount of fuel by increasing the duration of the pulse to the nozzle.
If the increased fuel demand is too great due to a sharp opening of the throttle, then the ECU can add asynchronous pulses to the injector in between synchronous intervals, which during normal operation are one for each reference pulse from the crankshaft position sensor.
Power enrichment mode
The ECU monitors the throttle position sensor signal and engine speed to determine when the driver needs maximum engine power. A rich fuel mixture is required to achieve maximum power, and the ECU changes the air/fuel ratio to approximately 12:1. In this mode, the signal from the oxygen concentration sensor is ignored, since it will indicate a rich mixture.
Braking lean mode
When braking a car with a closed throttle, emissions of toxic components into the atmosphere can increase. To prevent this, the electronic control unit monitors the decrease in the throttle opening angle and the pressure in the intake pipe and reduces the amount of fuel supplied in a timely manner by reducing the injection pulse.
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. Fuel cut-off occurs when all of the following conditions are met:
- coolant temperature above 44°C;
- crankshaft speed above 3150 rpm;
- vehicle speed above 42 km/h;
- throttle valve closed;
- absolute pressure sensor signal indicates no engine load (pressure less than 24 kPa);
- a table embedded in the permanent memory of the ECU and comparing the speed of the crankshaft with the speed of the vehicle determines the gear of the gearbox engaged.
When the vehicle is under engine braking, any of the following conditions will cause the fuel injection pulses to resume:
- crankshaft speed below 2100 rpm;
- vehicle speed less than 42 km/h;
- throttle valve is open at least 2%;
- the signal of the absolute pressure sensor in the intake pipe indicates the presence of a load (pressure over 25 kPa);
- clutch is off. This can be determined by the rapid drop in engine speed.
Voltage drop 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 current accumulation time in the ignition coil when the supply voltage drops below 12 V, and when the voltage drops below 8 V, by increasing the idle speed and the duration of the injection pulse.
Fuel cut mode
When the ignition is off, the nozzle does not supply fuel, which excludes the self-ignition of the mixture when the engine is overheated. In addition, fuel injection pulses are not given if the ECU does not receive crankshaft position reference signals, i.e. this means the engine is not running.
The fuel supply is also cut off when the maximum permissible engine speed of 6500 rpm is exceeded. Injection pulses will resume after the engine speed drops below 5850 rpm.
Cooling fan control
The electric fan is turned on and off by the ECU depending on the temperature of the engine, the speed of the crankshaft, the operation of the air conditioner (if it is on the car) and other factors. The electric fan is switched on using the auxiliary relay P4 (see fig. Injection wiring diagram), located in the mounting block.
When the engine is running, the electric fan turns on if the coolant temperature exceeds 104°C or a request is made to turn on the air conditioner. The electric fan turns off after the coolant temperature drops below 101°C, after the air conditioner is turned off or the engine is stopped.