Operation

Cold Engine Start: The control unit receives engine temperature information from the coolant temperature sensor. The colder the engine, the longer the injection period, which creates a fuel-rich starting mixture.

Warm-Up Phase: The temperature sensor informs the control unit of the gradual warming of the coolant through changing resistance values.

Idle: The idle switch informs the control unit of this operating condition. The throttle valve positioner regulates the idle speed and compensates for the speed drop caused by switching on high-power electrical consumers, the power steering being turned fully to one side, the automatic transmission being engaged in a drive position, or the air conditioner being switched on. This is done by changing the ignition timing.

Normal Operation: The control unit receives engine operating information from the speed pulses supplied by the Hall sensor and from resistance values of the throttle valve potentiometer (throttle valve position). From this, the control unit determines the engine load condition and meters the required amount of fuel through the injector to match the incoming air.

Lambda Control: When metering fuel, an air-fuel ratio of λ = 1 is maintained. Constant alternation between rich and lean mixture enables optimum operation of the catalytic converter.

Acceleration: Based on signals from the potentiometer, the control unit recognizes a sudden press of the accelerator pedal as acceleration, and the mixture is immediately enriched.

Full Load: At full throttle, or more precisely at a throttle valve position of about 72.5°, the control unit enriches the air-fuel mixture for full-load operation. Therefore, the mixture contains proportionally more fuel. The potentiometer reports the throttle valve position. However, during full-load mixture enrichment, the lambda sensor signal is ignored.

Overrun Fuel Cut-Off (Coasting): When driving downhill with the accelerator pedal released, the Mono-Motronic injection system saves fuel and shuts off fuel supply as soon as the engine reaches operating temperature. The control unit recognizes this operating condition from the released accelerator pedal (throttle valve potentiometer), signals from the coolant temperature sensor, and engine speed above 1500 – 1900 rpm (Hall sensor).

Engine Speed Limitation: If maximum engine speed is exceeded, the control unit cuts off fuel supply to protect the engine. Speed limitation cannot be achieved by switching off the ignition, because unburned fuel would then enter the catalytic converter. This could cause dangerous temperature increases and, consequently, long-term damage to the catalytic converter.

Emergency Operation: If the signal from one of the information sensors is missing entirely or has an implausible value, the Mono-Motronic injection system continues to operate normally. The control unit has so-called substitute values stored in its memory. Such a substitute value cannot, of course, account for many operating conditions, but the vehicle remains drivable. The driver may notice a sensor signal failure from reduced engine power or poor starting characteristics.