Misfire Monitor
Misfire Monitor
A misfire is caused by a failure of combustion. When this occurs, unburned HC and excess oxygen are exhausted from the cylinder. Consequently, the catalytic converter may suffer damage through overheating as it tries to convert the excessive HC. Secondly, the O2S will report a lean condition to the ECM, which in turn will increase the injector pulse width and add more raw fuel to the exhaust stream.
The misfire detection monitor is continuous and is designed to detect levels of misfire that can cause thermal damage to the catalyst and/or result in excessive tailpipe emissions. Determination of a misfire is made by analysis of changes in crankshaft speed, a misfire causing a drop in acceleration after an anticipated firing event. This data is analyzed in four ways to ensure all possible combinations of misfire can be detected.
The results of the misfire judgment process on each firing event are used to determine whether two failure levels have been met, 'catalyst damage' misfire and 'excess emissions' misfire. Each fault judgment process has its own failure threshold and calculation period.
Monitor DTCs
P0300 Random/multiple cylinder misfire
P0301 Cylinder 1 (1 bank 1) misfire
P0302 Cylinder 2 (1 bank 2) misfire
P0303 Cylinder 3 (2 bank 1) misfire
P0304 Cylinder 4 (2 bank 2) misfire
P0305 Cylinder 5 (3 bank 1) misfire
P0306 Cylinder 6 (3 bank 2) misfire
P0307 Cylinder 7 (4 bank 1) misfire (V8 engines only)
P0308 Cylinder 8 (4 bank 2) misfire (V8 engines only)
P1313 Catalyst damage misfire, bank 1
P1314 Catalyst damage misfire, bank 2
P1316 Excess emissions misfire
Monitoring Strategy
The misfire monitor operates continuously within the boundaries of the regulated monitor operation window, as shown below:
After engine start, the monitor will enable as soon as the engine speed rises above the minimum operation speed (150 RPM below fully warm stabilized idle speed). Two revolutions of crank angle data, i.e. One sample of data from each cylinder firing, are 'buffered' before any decisions can be made by the monitor. Before engine speed has reached the top of the start flare the monitor will be ready to make misfire judgments, which are then made on every cylinder firing, irrespective of whether the monitor is enabled or not.
Misfire Detection
For the purposes of misfire detection, "steady - state" is defined as:
- At least 1 second since fuel cut-off was last invoked.
- At least 1 second since gear change was last made.
- At least 0.5 seconds since rough road detected (1 second for 3.0L).
- At least 1 second since acceleration ignition retard was last invoked.
- At least 1 second since >15% shunt control ignition retard was last invoked (3.0L only).
- At least 1 second since fuel cut-off ignition retard was last invoked.
- At least 1 second since ISC feedback status (off to on only) changed.
- At least 1 second since A/C status (on or off) changed.
- At least 1 second since electrical load status (on or off) changed.
- At least 1 second since traction control ignition retard was last invoked.
- Rate of change of engine speed less than 250 RPM/0.064s.
- Rate of change of engine load has been less than 0.1g/revolution for at least 20 firing cycles.
- Rate of change of throttle angle is less than 1.5 degrees/0.008s.
