Table of contents: Control unit ↓ Throttle valve ↓ Combustible mixture preparation unit ↓ Injection nozzle ↓ Temperature sensor ↓ Pressure regulator ↓ Throttle position controller ↓ Throttle potentiometer ↓
Control unit
It is located in the front passenger footwell area in front of the heating duct and receives information from the following units via a multi-pin plug:
Hall sensor in the ignition distributor - about the engine speed.
Lambda probe in the catalytic converter - about the content of residual oxygen in the exhaust gases.
Potentiometer - about the position of the throttle valve and the amount of incoming air.
The incoming air temperature sensor at the entrance of the combustible mixture preparation unit - about the incoming air temperature.
Temperature sensor on the coolant pipe on the left side of the cylinder head - about the coolant temperature.
By processing the incoming signals, the control unit calculates the duration of the electromagnetic injector opening and thus the amount of fuel injected. In doing so, the control unit uses the multi-parameter characteristics of the engine - a file in which all possible engine states are recorded. Information on the amounts of fuel related to a particular situation is also recorded there in the form of electrical signals. Additionally, the ignition timing indicators related to the amount of fuel and the operating situation are stored in the Mono-Motronic in the form of characteristics.
Throttle valve
It is located at the very bottom of the fuel mixture preparation unit and regulates the amount of air that the engine should receive. The degree of opening of the valve is determined by the driver when pressing the accelerator pedal. The pedal and the throttle valve are directly connected to each other by means of a cable drive of the accelerator.
Combustible mixture preparation unit
Most of the components of the central petrol injection system are assembled in this housing. The incoming air passes through it, and here - via the nozzle - fuel is added, as in the carburetor.
Injection nozzle
It is opened by an electromagnet. Thus, fuel can flow - or not - depending on the signal from the control unit. For optimal fuel atomization, the injector is equipped with beveled outlet holes, through which gasoline enters the conical wall of the outlet hole, swirling there.
The injection nozzle can only open and close, but is not able to dose the amount of fuel. Therefore, it is regulated by the injection time. This is done as follows: the nozzle injects once with each high-voltage current pulse or Hall sensor. If a small amount of fuel is required, the nozzle opens with this pulse only for a short time. If the engine needs more fuel, the injection occurs for a longer time. And so on with each pulse of the Hall sensor.
Functional diagram of the Mono-Motronic injection system. The fuel in the system is shown in red, and the inlet air is shown in light pink.
Temperature sensor
It is located on the side of the injector body and can thus accurately determine the temperature.
Pressure regulator
The fuel pump supplies gasoline under pressure to the pressure regulator, which ensures that gasoline reaches the injector under the same pressure of 0.8-1.2 bar. It allows some gasoline to flow back into the fuel tank through the drain line. The supply through the fuel filter remains almost constant.
Throttle position controller
A small electric motor with an angular transmission moves the drive tappet closer to or further from the idle stop of the throttle valve. This allows the throttle valve to open more or less depending on the situation. This keeps the idle speed constant under different loads. An idle signal switch is located in the drive tappet of the throttle position controller, which tells the control unit when you release the accelerator pedal.
Throttle potentiometer
It informs the control unit about the movements of the throttle valve and its position. For example, a rapid opening of the throttle valve is recognized as acceleration of the car. If you remove your foot from the accelerator pedal, the throttle valve closing signal activates the cessation of fuel supply in idle mode.