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2003 3BMXV03.0UL2

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  1. Measurement Principle -  Method of engine misfire detection is based on monitoring crankshaft acceleration. Engine roughness is derived from differences of segment period (90 degree crank angle) durations that are corrected and compared to load and engine-speed dependent thresholds. Different statistical methods are used to distinguish between normal changes of segment duration and changes due to misfire. See Figure. Segment periods are measured through an angular range of 90 degree crank angle. Segment starts at 54 degrees before TDG. Beginning and end of segments are located at same angle. Duration of crankshaft segments is measured continuously.
  2. Sensor Wheel Adaptation -  To eliminate manufacturing tolerances and off-center installation, adaptation of sensor wheel tolerances is carried out during fuel cut-off. Segment periods are corrected by adaptation values. With progressing adaptation, sensitivity of misfire detection is improved.
  3. 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, base value is multiplied by a coolant temperature dependent correction value. Without sufficient sensor wheel adaptation, engine roughness threshold is limited depending on wheel tolerances expected. See Figure.
  4. Fault Processing (Error Window) -  Within an interval of 200-1000 crankshaft revolutions, "error windows" to check for similar engine conditions are determined. Upon detection of misfire, window is extended if current operating point is not within the window.
  5. Engine Operating Point Window -  Engine-operating window is updated with each segment without detected misfire.
  6. Misfire Detection (Emission Increase) -  Within an interval of 1000 crankshaft revolutions (3000 segments), detected misfire events are added for each cylinder. If sum of all cylinder misfire incidents exceeds a predetermined value, a fault code is stored. If more than one cylinder is misfiring, all misfiring cylinders will be specified and individual fault codes for all misfiring cylinders and for multiple cylinders will be stored.
  7. Misfire Detection (Catalyst Damage) -  Within an interval of 200 crankshaft revolutions, detected number of misfiring events is weighted and calculated for each cylinder. The weighting factor is determined using a load/speed dependent map. If sum of cylinder misfire incidents exceeds a predetermined value, a fault code is stored and MIL is illuminated. If cylinder selective count exceeds predetermined threshold, following measures take place:
    • Fuel control system is switched from closed-loop to open-loop operation.
    • Cylinder selective fault code is stored.
    • If more than one cylinder is misfiring, fault codes for all individual cylinders and for multiple cylinders will be stored.
    • Fuel supply to respective cylinder is cut off. See Figure.
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