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Home >> Jaguar >> 2014 >> XK Base, 2D Coupe >> Repair and Diagnosis >> External Pages >> Different car >> Section 91 (Electronic Engine Controls - V8 S/C 5.0L Petrol -- XK/X150) >> Electronic Engine Controls - V8 S/C 5.0L Petrol >> Electronic Engine Controls >> Description And Operation >> Principles Of Operation >> Misfire Detection

Misfire Detection

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Legislation requires that the ECM must be able to detect the presence of an engine misfire. It must be able to detect misfires at two separate levels. The first level is a misfire that could lead to the legislated emissions limit being exceeded by a given amount. The second level is a misfire that may cause catalytic converter damage.

The ECM monitors the number of misfire occurrences within two engine speed ranges. If the ECM detects more than a predetermined number of misfire occurrences within either of these two ranges, over two consecutive journeys, it will record a fault code and details of the engine speed, engine load and engine coolant temperature. In addition, the ECM monitors the number of misfire occurrences that happen in a 'window' of 200 engine revolutions. The misfire occurrences are assigned a weighting according to their likely impact on the catalytic converters. If the number of misfires exceeds a given value, the ECM stores catalytic converter damage fault codes, along with the engine speed, engine load and engine coolant temperature.

The signal from the CKP sensor indicates how fast the poles on the drive plate are passing the sensor tip. A sine wave is generated each time a pole passes the sensor tip. The ECM can detect variations in drive plate speed by monitoring the sine wave signal supplied by the crankshaft position sensor. By assessing this signal, the ECM can detect the presence of an engine misfire. At this time, the ECM will assess the amount of variation in the signal received from the CKP sensor and assign a roughness value to it. This roughness value can be viewed within the real time monitoring feature using Jaguar approved diagnostic equipment. The ECM will evaluate the signal against a number of factors and will decide whether to record the occurrence or ignore it. The ECM can assign a roughness and misfire signal for each cylinder.

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