2003 3BMXV06.0N73

WARNING: This page does not describe the selected car, but rather 18 other vehicles, including the 2002 BMW Z8, 2002 BMW Z3, 2002 BMW X5, 2002 BMW M5, and 2002 BMW M3. However, it is still accessible from the selected car via links, so may be relevant.

Misfire Monitoring - Misfire detection is based on evaluating engine speed fluctuations. To detect misfiring at any cylinder, torque of each cylinder is evaluated by metering time between 2 ignition events, which is a measure for mean value of speed of this angular segment. This means that a change of engine torque results in a change of engine speed. Additionally, influence of load torque will be determined, such as influences of different road surfaces, (pavement, pot holes etc.) If mean engine speed is to be measured, influences caused by road surfaces have to be eliminated. This method consists of following main parts:
- Data acquisition, adaptation of sensor wheel is included.
- Calculation of engine roughness.
- Comparison with a threshold depending on operating points.
- Some extreme conditions, during which misfire detections should be disabled for a short time.
- Fault processing, counting procedure of single misfire events. See Figure.
Monitoring Cycle - Monitoring cycle is represented by the following:
- Data Acquisition - Duration of crankshaft segments is measured continuously for every combustion cycle.
- Sensor Wheel Adaptation - Within a defined engine speed range and during fuel cut-off, adaptation of sensor wheel tolerances is carried out instead of misfire detection. After this, total operation range of engine is corrected to equalize engine roughness across all cylinders. Thereafter, maximum sensitivity to engine roughness at a given load/speed site is achieved. With progressing adaptation, sensitivity of misfire detection is increasing. Adaptation values are stored in a non-volatile memory and taken into consideration for calculation of engine roughness.
Misfire Detection - Following operating steps are performed for each measured segment corrected by sensor wheel adaptation:
- Calculation Of Engine Roughness - Engine roughness is derived from the differences of segment durations. Different statistical methods are used to distinguish between normal changes of segment duration and changes due to misfiring.
- Detecting Of Multiple Misfiring - If several cylinders are misfiring (alternating one combustion/one misfire event) calculated engine roughness values may be so low that threshold is not exceeded during misfiring and therefore misfiring would not be detected. Based on this, periodicity of engine roughness value is used as additional information during multiple misfiring. Engine roughness value is filtered and a new multiple filter value is created. If this filter value increases due to multiple misfiring, roughness threshold is decreased. By applying this strategy, multiple misfiring is detected reliably.
- Calculation Of Engine Roughness Threshold Value - Engine roughness threshold value consists of base value, which is determined by a load/speed dependent map. During warm-up, coolant temperature dependent correction value is added. In case of multiple misfiring, threshold is reduced by an adjustable factor. Without sufficient sensor wheel adaptation, engine roughness threshold is limited to a speed dependent minimum value. A change of threshold toward a smaller value is limited by a variation constant.
Determination Of Misfiring - Misfire detection is performed by comparing engine roughness threshold value with engine roughness value. If a misfire event is detected in a cylinder, misfire detection of next cylinder in firing order is deactivated to prevent a faulty diagnosis.
- Fault Processing Statistics - Within an interval of 1000 crankshaft revolutions, detected misfiring events are added for each cylinder. If sum of all cylinder misfire incidents exceeds a predetermined value, fault code for emission relevant misfiring is preliminarily stored. If only one cylinder is misfiring, a cylinder selective fault code is stored. If more than one cylinder is misfiring, fault code for multiple misfiring is also stored. Within an interval of 200 crankshaft revolutions, detected number of misfiring events is weighted and calculated for each cylinder. Weighting factor is determined by a load/speed dependent map. If sum of cylinder misfire incidents exceeds a predetermined value, fault code for indicating catalyst damage relevant misfiring is stored and MIL is illuminated. If cylinder selective count exceeds predetermined threshold, following measures take place:
  1. Lambda closed loop system is switched to open-loop.
  2. Cylinder selective fault code is stored. If more than one cylinder is misfiring, fault code for multiple misfire is also stored.
  3. Fuel supply to respective cylinder is cut-off.
  All misfire counters are reset after each interval. See Figure.