Pic. 175. Mono-Jetronic injection system: 1 - central nozzle; 2 - fuel pressure regulator; 3 - temperature sensor of the cooling system; 4 - electronic control unit; 5 - idle speed regulator; 6 - switch on the throttle shaft; 7 - electric fuel pump; 8 - fuel filter
Fuel is supplied to the central nozzle by an electric fuel pump located in the fuel tank and by the main pump through the fuel filter. The fuel pressure regulator provides a constant pressure of approximately 1 kg/cm2, regardless of the amount of fuel injected.
Air for the working mixture is sucked in by the engine through the air filter and throttle valve. The angular position of the throttle valve deflected when the accelerator pedal is depressed is measured by a potentiometer and serves as a measure of the intake air quantity for the control unit, together with the engine speed.
The control unit regulates the duration of fuel injection and thus the amount of injected fuel in accordance with the amount of air sucked in. With a longer opening of the nozzle, more fuel is injected. Additional sensors ensure that the injected fuel is metered under all driving conditions.
The throttle shaft switch is located directly on the throttle shaft. When the throttle valve is in the idle position, it sends a corresponding signal to the control unit. At the same time, the control unit automatically switches the engine to the set value of the idle speed, respectively opening and closing the throttle valve through the actuator motor. This ensures that the engine runs smoothly at low idle regardless of engine temperature.
The temperature sensor in the intake tract measures the air temperature. The intake air temperature is taken into account by the control unit when metering the injected fuel.
The intake tract heater functions in the same way as on carburetor engines, affecting fuel deposits in the intake pipe.
The oxygen sensor measures the oxygen content in the exhaust gas stream and transmits a corresponding electrical signal to the control unit. Based on this information, the control unit changes the composition of the intake air-fuel mixture in such a way as to ensure optimal afterburning of the exhaust gases in the catalyst.
The Mono-Jetronic fuel injection system requires virtually no maintenance other than replacing the air filter element every 30,000 km.
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