Misfire Detection Monitor

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 occurred. The misfire event is defined as poor compression, fuel delivery or mechanical engine concern. The powertrain control module (PCM) uses the crankshaft position (CKP) and camshaft position (CMP) sensor signals when detecting the misfire. The input signal generated by the CKP sensor is derived by sensing the passage of the teeth from the crankshaft position wheel, which is mounted on the crankshaft. The input signal to the PCM is used to calculate the time between CKP edges and also crankshaft rotational velocity and acceleration. The PCM uses both; CKP and the CMP sensor signal information to determine which cylinder misfired.

A cylinder balancing strategy is used to detect cylinders that are contributing too much or too little torque in respect to other cylinders. 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 is met, the suspect cylinder is determined to have misfired.

The misfire detection monitor is enabled and runs continuously only when certain base engine conditions are first satisfied. The typical monitoring duration for this monitor is 1 minute. Inputs from the exhaust gas recirculation (EGR) valve position, exhaust pressure (EP), intake air temperature (IAT), engine coolant temperature (ECT), fuel rail temperature (FRT), engine oil temperature (EOT), vehicle speed (VSS), fuel rail pressure (FRP) sensors and the fan speed (FSS) sensor are required to enable the monitor. The monitor entry conditions include:
- Operational EGR valve and position sensor
- No EGR flow monitor concerns
- No exhaust pressure control errors
- Operational fuel pressure control valve
- Operational fuel volume control valve
- Correct low fuel pressure at engine crank
- System voltage within range
- No brake switch, cooling fan and charging system concerns
- Engine speed between 500 and 950 RPM
- Vehicle speed between 0 km/h (0 mph) and 10 km/h (6.2 mph)
- ECT between -40°C (-40°F) and 120°C (248°F)
- FRT and EOT greater than -20°C (-4°F)
- IAT between -40°C (-40°F) and 100°C (212°F)

Upon detection of a misfire which exceeds the emissions threshold or causes a vehicle to fail an inspection and maintenance tailpipe emissions test, the MIL illuminates and a DTC is stored. The DTC associated with multiple cylinder misfire is DTC P0300. The DTCs associated with cylinder misfire are P0301, P0302, P0303, P0304, P0305, P0306, P0307, and P0308.