Table of contents: Starting a cold engine ↓ Warming up the engine ↓ Idling ↓ Acceleration, acceleration ↓ Regulation of CO content ↓ Forced idle mode ↓ Full operating load ↓ Engine speed limitation ↓ Emergency program ↓
Starting a cold engine
When starting a cold engine, the idle stabilization valve increases the intake air through a separate channel. At the same time, the system control unit receives information from the coolant temperature sensor that the engine is cold. The control unit responds to the information received by increasing the duration of fuel injection, ensuring the formation of a fuel-enriched mixture. In addition, the control unit includes a starting fuel solenoid valve, which sprays an additional portion of fuel in the intake manifold.
Warming up the engine
The coolant temperature sensor informs the electronic control unit about the increase in coolant temperature. In response to this information, the control unit closes the idle speed stabilization valve, and the fuel injection duration is reduced and maintained within normal values.
Idling
The electronic control unit recognizes the idle mode based on information coming from the throttle angle potentiometer and the potentiometer on the air flow meter. When the engine speed decreases at idle, the control unit changes the ignition timing. At the same time, the idle stabilization valve opens, supplying additional air and causing a slight increase in the volume of injected fuel.
In the design operating mode, all auxiliary components of the system are usually not involved. The position of the throttle valve and the valve shutter of the air flow meter are decisive for the duration of the injector opening.
Acceleration, acceleration
The electronic control unit receives information about the rapid opening of the throttle valve from a message from the throttle valve angular position potentiometer and responds to this by increasing the duration of the injector opening.
Regulation of CO content
In order for the catalyst to work flawlessly, it requires constant alternation of enriched and lean air-fuel mixtures. Information about the oxygen level in the exhaust gases at the current moment is reported to the electronic control unit by the oxygen sensor (lambda probe) on the catalyst. The electronic control unit reacts to this in a split second by reducing or increasing the duration of the injector opening, thereby regulating the composition of the air-fuel mixture.
Forced idle mode
Information that the driver has released the accelerator pedal also reaches the control unit from the throttle angle potentiometer. And if the coolant temperature sensor informs the control unit that the engine is at operating temperature, and the Hall sensor informs that the engine speed is above 1500 rpm, the control unit closes the injectors.
Full operating load
To operate at full load, the engine requires more fuel. The electronic control unit recognizes this mode based on data from the throttle angle potentiometer and increases the duration of the injector opening. The lambda probe signals are ignored.
Engine speed limitation
To protect the engine, the electronic control unit switches off the injectors when it receives information from the Hall sensor that the engine speed is 6400-6500 rpm.
Emergency program
In the event of failure of one of the sensors, disruption of the necessary contact with the corresponding sensor, or a situation where the sensor begins to give meaningless information, the Digifant system continues to function. For this case, the memory of the electronic control unit contains data from the so-called emergency program, which cannot be changed. This program cannot take into account much of what is normally perceived by the system, but it maintains engine operation. A decrease in the effective engine power or deterioration in its start-up are evidence of the failure of one of the sensors.
The control unit recognizes and records some of the engine malfunctions in a memory device (storage device). During service work and during vehicle maintenance, workshops interrogate the memory device using the appropriate VAG 1551 device and print out the entire list of registered faults. If the vehicle owner suspects a fault in the fuel injection system, he can contact the workshop and receive a corresponding fault printout, as well as professional assistance in eliminating the defect. After the fault has been eliminated, it is removed from the list.
Caution! When performing checks or adjustments that involved disconnecting the coolant sensor plug, the self-diagnosis device registers the absence of a signal from this sensor. For this reason, after performing work involving disconnecting the coolant sensor plug, it is recommended that you contact a workshop to print out and delete records of this malfunction.