dx2
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Misfire Detection Monitor
The misfire detection monitor is an on board strategy designed to monitor engine misfire and identify the specific cylinder in which
the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor
compression, or any other cause. The misfire detection monitor is enabled only when certain base engine conditions are first
satisfied. Input from the engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), and
mass airflow (MAF) sensor (if equipped) is required to enable the monitor. The misfire detection monitor is also carried out during
an on-demand self-test.
1. The PCM synchronized ignition spark is based on information received from the crankshaft position (CKP) sensor. The CKP
sensor signal generated is also the main input used in determining cylinder misfire.
2. The input signal generated by the CKP sensor is derived by sensing the passage of teeth from the crankshaft position wheel
mounted on the end of the crankshaft.
3. The input signal to the PCM is then used to calculate the time between CKP sensor signal edges and the crankshaft
rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is
determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value and other criteria are met,
then the suspect cylinder is determined to have misfired.
4. The malfunction indicator lamp (MIL) is activated after one of the above tests fail on 2 consecutive drive cycles.
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