System Adaptations

OPERATION
The fuel-air mixture formed in the intake tract requires a certain period of time until it reaches the oxygen sensor in the form of exhaust gas. This time decreases as load and engine speed increase. For this reason, the response time of the emission control system is also dependent on load and engine speed. Mixture deviations detected by the oxygen sensor result in storage of adaptation values (learned correction values). By way of these adaptations, the injection can be set close to the nominal values in advance, thus achieving a reduction in the response time.

For instance, if the basic injection values for the Digital Motor Electronic (DME) characteristic map are too low during idling in order to maintain the ideal fuel-air mixture, the emission control system would have to constantly increase the injection timing. In this case, an adaptation value is learned which corrects the basic injection value. The emission (lambda) control then only needs to undertake the fine adjustment.

Following adaptations are performed during engine operation:
Fuel Evaporation Control Adaptation
When the fuel evaporation control valve is open, an additional combustible mixture or air is supplied to the engine from the activated carbon filter. The shift in the air/fuel ratio detected by the oxygen sensor is almost completely compensated by way of the fuel evaporation control adaptation value.

Idle Air Adaptation
In conjunction with the idle actuator, the idle air adaptation ensures constant idle speeds.

Idle Mixture Adaptation
If the idle signal is applied during the rest phase of the fuel evaporation control valve, idle mixture adaptation takes place at certain intervals.

Part Load Mixture Adaptation
Also in the part load range, mixture adaptation takes place at certain intervals. The determined adaptation value is taken into account in all part load ranges.

The correction values stored in the control unit are intended as additional information only In the case of acute engine problems.

If problems occur during engine operation and no defect codes are stored in the defect code memory, the mixture adaptation values can be read out on the BMW Service Tester. These values can provide an indication as to which direction troubleshooting is to be continued.

The adaptation values are lost (forgotten) when the voltage supply to the DME is interrupted. This can lead to starting and idle running problems. Depending on how far the adaptation values deviated from the basic values, a considerable period of time is required until the adaptation values are relearned.

For this reason, Idle operation or test runs are of little use in order to observe the change in the adaptation values.