Operation

Cold start: The idle speed control valve allows some air to enter in addition to the air flowing through the normal path. At the same time, the control unit receives a "cold engine" signal from the coolant temperature sensor. Based on all this data, the control unit calculates a longer opening time for the fuel injectors to produce a richer mixture. In addition, the control unit briefly activates the cold start valve to supply an additional quantity of fuel.

Engine warm-up phase: The coolant temperature sensor reports the rising coolant temperature to the control unit. The control unit then commands the idle speed control valve to close, and the fuel injector opening duration is reduced to normal.

Idle: From the signals of the throttle valve potentiometer and the air flow meter potentiometer, the control unit recognizes when the engine is running at idle. If idle speed drops, the control unit changes the ignition timing; at the same time, the idle speed control valve opens its air passage, which increases the amount of injected fuel.

Normal operation does not require any special adjustments. The duration of fuel injector opening is determined by the position of the throttle valve and the air flow meter sensor plate.

Acceleration: The control unit recognizes rapid opening of the throttle valve from the throttle valve potentiometer signals as acceleration. Accordingly, the injection duration is briefly increased.

Lambda control: For proper catalytic converter operation, the mixture must be constantly alternated between rich and lean. The lambda sensor (located in the catalytic converter) reports the residual oxygen content at any given moment to the control unit, which within fractions of a second commands the fuel injectors to shorten or lengthen the injection time and thus the fuel quantity.

Fuel cut-off during overrun: When the accelerator pedal is released, this information is again sent to the control unit via the throttle valve potentiometer. If the coolant temperature sensor simultaneously reports that the engine has reached operating temperature, and the Hall sensor in the distributor reports that engine speed is above 1500 rpm, the control unit does not command the fuel injectors to open.

Full load: To develop full power with the accelerator pedal fully depressed, the engine requires more fuel. Based on the "full throttle" signal from the throttle valve potentiometer in combination with the fully open air flow sensor plate, the control unit recognizes the "full load" condition and increases the injector opening duration, while the lambda sensor signal is ignored.

Speed limitation: To protect against exceeding the maximum permissible engine speed, the control unit cuts off the fuel injectors when the Hall sensor reports an engine speed of 6400 – 6500 rpm.

Emergency operation: If the signal from one of the information sensors is missing entirely or has an implausible value, the Digifant injection system continues to operate normally under these conditions. The control unit uses a so-called substitute value already stored in memory. It cannot, of course, account for many operating conditions, but the vehicle remains drivable. The driver may notice a sensor failure from reduced power or poor starting performance.