Starting a cold engine
The fuel injection system electronic control unit receives information about the engine temperature from the coolant temperature sensor. The lower the temperature of the engine itself, the longer the injector stays open to provide maximum fuel for a highly enriched air-fuel mixture.
Engine warm-up
The coolant temperature sensor transmits information about a gradual increase in coolant temperature to the electronic control unit in the form of electrical signals about a change in the resistance value. Accordingly, there is a gradual reduction in the duration of the injector in the open state. In this state of the engine, the signals from the lambda probe are ignored. This means that the air-fuel mixture during this period of engine operation is not optimal for the catalyst.
Idling
The idle speed sensor on the throttle valve control unit informs the injection system control unit about the operating position of the throttle valve. The throttle valve control determines the idle speed and at the same time equalizes the idle speed, which is necessary due to the inclusion of an increasing number of electrical consumers, the operation of the power steering, the gear engaged in cars with automatic transmission or due to the air conditioner. This adjustment of the idle speed is possible by changing the ignition timing and, accordingly, the ignition timing (see illustration 2.0a).
Design operation mode
The electronic control unit receives information about the operation of the engine in the form of pulses about the engine speed from the Hall sensor, as well as about the throttle position from the potentiometer. Based on this data, the control unit recognizes the operating load on the engine and determines the required amount of fuel that the injector must inject to prepare the air-fuel mixture.
When determining the amount of fuel injected by the injector, the content of fuel and air in the mixture is taken into account at a value of (= 1. A constant combination of rich and lean air/fuel mixture ensures optimal catalyst performance.
The electronic control unit perceives pressing the accelerator pedal as a potentiometer signal about the need to increase speed and immediately «gives a command» for the preparation of an enriched air-fuel mixture.
Full operating load
At full operating load, more specifically at a throttle angle of 72.5°, the electronic injection system control unit provides the preparation of an air-fuel mixture that meets the needs of the engine in this mode of operation. This means that the specific fuel content in the mixture increases. When the mixture is enriched, the lambda probe signals are ignored.
Forced idle mode
When driving downhill with the accelerator pedal inactive, the Mono-Motronic system conserves fuel and shuts it off when the engine is warmed up to operating temperature. The system control unit recognizes this situation from the throttle potentiometer on the released pedal «gas», according to information from the coolant temperature sensor and from the Hall sensor about engine speeds that are in the range of 1500-1900 rpm.
Engine speed limitation
If the permissible maximum engine speed is exceeded, the electronic control unit cuts off the fuel supply to protect the engine. Limiting the engine speed by switching off the ignition is not possible, because unburned fuel would then enter the catalyst, which is fraught with damage.
Emergency program
If one of the sensors fails, if the necessary contact with the corresponding sensor is broken, or if a situation arises when the sensor starts to give out meaningless information, the Mono-Motronic system continues to function. In this case, the memory of the electronic control unit contains the data of 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 keeps the engine running. The driver feels the activation of the emergency program by a drop in the effective power of the engine or by difficult starting of the engine.
The control unit recognizes and registers some of the malfunctions in the operation of the engine in a memory device (drive). If the registered error or malfunction does not reoccur during the next ten engine starts (sporadic function failure), then this fault is automatically deleted from the compiled list. Permanent faults are read and printed using a special device connected to the diagnostic socket. As a rule, workshops do this during service work and during vehicle maintenance. Reading and printing of fault codes by the motorist himself is not possible. If the owner of the car assumes a malfunction of the fuel injection system, then by contacting the workshop, he can receive the appropriate printout of the faults, as well as professional assistance in eliminating the defect. After the problem is fixed, it is removed from the list.
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