Misfire Detection Monitor

The misfire 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 monitor will be enabled only when certain base engine conditions are first satisfied. Input from the Engine Coolant Temperature (ECT), Measuring Core-Variable Air Flow (MC-VAF) or Mass Air Flow (MAF), and Crank Position (CKP) sensors is required to enable the monitor. The misfire monitor is also performed during on demand self-test. To aid in monitor definition, refer to illustration. See Fig 1.

1. The PCM synchronized ignition spark based on information received from the CKP sensor. The CKP 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 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 edges and also 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 is met, then the suspect cylinder is determined to have misfired.
4. Misfire detection types:
   • Misfire Type (A). Upon detection of a Misfire type A: (200 revolutions) which would cause catalyst damage, the MIL will blink once per second during the actual misfire, and a DTC will be stored.
   • Misfire Type (B). Upon detection of a Misfire type B: (1000 revolutions) which will exceed the emissions threshold or cause a vehicle to fail an inspection and maintenance tailpipe emissions test, the MIL will illuminate and a DTC will be stored.

   The DTC associated with multiple cylinder misfire for a Type A or Type B misfire is DTC P0300.

   The DTCs associated with an individual cylinder misfire for a Type A or Type B misfire are DTCs P0301, P0302, P0303, 0304, 0305, P0306, P0307, and P0308, P0309 and P0310.

Fig 1: Identifying Misfire Monitor Components

Courtesy of FORD MOTOR CO.