Operating principle of the electronic engine management system (Audi A4 B6)

During a cold start, the throttle control increases the amount of air admitted. The control unit receives information from the coolant temperature sensor about the low engine temperature and calculates a longer duration of opening of the valve injectors. If the temperature sensor reports that the coolant is warming up, then the stabilization of the idle speed is stopped, and the duration of injection is reduced towards the normal duration. The duration of injection in normal mode in this case depends, first of all, on the position of the throttle valve and the data received from the air flow meter.

In idle mode, the control device changes the ignition timing if the engine speed falls below the permissible value. Additionally, the throttle control device can increase the air flow and, with it, the amount of the injected mixture.

If the driver accelerates hard, for example when he wants to overtake, the control unit detects this by a sharp movement at the throttle position sensor. The injection duration increases for a while. In order to develop full power with the accelerator pedal fully depressed, the engine needs even more fuel. The control unit regulates the injection duration at full load in accordance with the signals from the throttle position sensor and the air flow meter. If the maximum speed is exceeded, the control unit switches off the injectors.

In the opposite case, i.e. when releasing the gas, the injectors remain in the fully closed position. However, the control device activates the fuel supply cut-off in the so-called forced idle mode only if the engine has warmed up to operating temperature and the speed reported by the sensor exceeds 1500 rpm. Cutting off the supply allows fuel to be saved.

To prevent the car from stopping immediately after one of the sensors fails or a sensor gives an incredible value, emergency running functions are programmed. Depending on the defect, the driver may not even notice this, but it may cause a loss of power or difficult starting.