Contents: Engine start mode ↓ Engine purge mode ↓ Open loop mode after start (no…↓ Closed loop mode after start (with…↓ Enrichment mode during acceleration ↓ Power enrichment mode ↓ Lean mode during braking ↓ Fuel shut-off mode during engine…↓ Supply voltage drop compensation ↓ Fuel Shut-Off Mode ↓ Control of the electric fan of the…↓
The amount of fuel supplied by the injector is regulated by an electrical pulse signal from the electronic control unit (ECU). It monitors engine condition data, calculates fuel requirements and determines the required duration of fuel supply by the injector (pulse duration). To increase the amount of fuel supplied, the pulse duration is increased, and to decrease the fuel supply, it is shortened.
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. The "self-learning" of the ECU is a continuous process that continues throughout the entire service life of the vehicle.
Usually, one pulse is supplied 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 coinciding with them in time. Synchronous fuel injection is the most commonly used method of fuel supply. Asynchronous fuel injection is used when additional fuel is required during a sharp opening of the throttle valve, which is signaled by the throttle position sensor. This fuel injection is similar to the fuel supply by the accelerator pump of the carburetor during a sharp opening of the throttle valve.
Regardless of the injection method, fuel supply is determined by the engine condition, i.e. its operating mode. These modes are provided by the ECU and are described below.
Engine start mode
When the ignition is turned on, the ECU switches 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 the readings from the coolant temperature and throttle position sensors and determines the correct air/fuel ratio for starting.
After the crankshaft starts rotating, the ECU will operate in the starting mode until the speed exceeds 420 rpm, otherwise it may switch to the engine "purge" mode. The duration of each pulse to the injector during starting is 4–6 ms, depending on the coolant temperature and the throttle position.
Engine purge mode
If the engine is "flooded with fuel", it can be started by fully opening the throttle valve while simultaneously cranking the crankshaft. In this mode, the ECU sends pulses to the injector corresponding to an air/fuel ratio of 26:1 (pulse duration is about 2 ms), which "cleans" the flooded engine. The ECU maintains the specified pulse duration as long as the engine speed is below 420 rpm and the throttle position sensor shows that it is almost fully open (more than 85%).
If the throttle is held almost fully open when attempting to start a "non-flooded" engine normally, the engine may not start because the 26:1 air/fuel ratio may not be sufficient to start a non-flooded engine, especially if it is not warmed up.
Open loop mode after start (no feedback)
After starting the engine (when the speed is more than 420 rpm) The ECU will control the fuel supply system in the "open loop" mode. In this mode, the ECU ignores the signal from the oxygen sensor and calculates the pulse duration to the injector based on signals from the crankshaft position sensor (rotation frequency information), absolute air pressure sensor, coolant temperature sensor and throttle position sensor.
In open-loop mode, the calculated injection pulse duration may result in an air/fuel ratio different from 14.7:1. An example would be a cold engine condition, since a rich mixture is required to ensure good drivability.
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 to operate normally;
- coolant temperature is greater than 32°C;
- the engine has been running for a certain period of time since it was started.
The time may vary from 6 sec to 5 min depending on the coolant temperature at the time of engine start. If the temperature was below 18°C, the period is 5 min. If the temperature was above 75°C, the delay is 6 sec.
Closed loop mode after start (with feedback)
In closed loop mode, the ECU first calculates the injector pulse width based on signals from the same sensors as in open loop mode. The difference is that in closed loop mode, the ECU also uses the signal from the oxygen sensor to adjust and fine-tune the calculated pulse to precisely maintain the air/fuel ratio at 14.6...14.7:1. This allows the catalytic converter to operate at maximum efficiency.
Enrichment mode during acceleration
The ECU monitors sudden changes in the throttle position (by throttle position sensor) and for the pressure in the intake pipe (by absolute pressure sensor) and ensures the supply of an additional amount of fuel by increasing the pulse duration to the injector.
If the increased fuel demand is too great due to a sharp opening of the throttle valve, the ECU can add asynchronous pulses to the injector in the intervals between synchronous pulses, of which, during normal operation, there is 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 requires maximum engine power. To achieve maximum power, a rich fuel mixture is required, and the ECU changes the air/fuel ratio to approximately 12:1. In this mode, the signal from the oxygen sensor is ignored, as it will indicate a rich mixture.
Lean mode during braking
When braking a car with a closed throttle valve, emissions of toxic components into the atmosphere may increase. To prevent this, the electronic control unit monitors the decrease in the throttle valve opening angle and the pressure in the intake pipe and promptly reduces the amount of fuel supplied by reducing the injection pulse.
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. Fuel supply is disabled when all of the following conditions are met:
- coolant temperature above 44°C;
- crankshaft speed above 3150 rpm;
- the vehicle speed is over 42 km/h;
- throttle valve closed;
- the absolute pressure sensor signal shows no engine load (pressure less than 24 kPa);
- a table embedded in the ECU's permanent memory that compares the crankshaft speed with the vehicle's speed determines the gear engaged in the transmission.
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;
- the vehicle speed is less than 42 km/h;
- the throttle valve is open at least 2%;
- the signal from the absolute pressure sensor in the intake manifold shows the presence of a load (pressure over 25 kPa);
- the clutch is disengaged. This can be determined by a rapid drop in crankshaft speed.
Supply voltage drop 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 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 Shut-Off Mode
When the ignition is off, the fuel is not supplied by the injector, which eliminates the possibility of spontaneous combustion of the mixture when the engine is overheated. In addition, fuel injection pulses are not supplied if the ECU does not receive reference signals from the crankshaft position, 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 6,500 rpm is exceeded. Injection pulses will resume after the crankshaft speed drops below 5,850 rpm.
Control of the electric fan of the cooling system
The electric fan is switched on and off by the ECU depending on the engine temperature, crankshaft speed, and air conditioning operation (if it is on the car) and other factors. The electric fan is switched on using the auxiliary relay P4 (see Fig. Electrical connection diagram of the injection system), 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.