Misfires can be caused by lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or many other causes. Even a small number of misfires may result in excessive exhaust emissions due to the unburned mixture. Increased misfire rates cause damage to the catalytic converter. The ECM monitors the crankshaft speed variation to determine if any misfiring generated. The ECM identifies the specific cylinder in which the misfire has occurred and counts individual misfire events by monitoring changes in the crankshaft rotation for each cylinder. A random misfire indicates one or more cylinders are misfiring.
If a misfire exists that exceeds the threshold value, P0300 is set.
Item | Detecting Condition | Possible Cause | |
DTC Strategy |
•
Engine roughness through crankshaft speed fluctuation | 1. Poor connection 2. Ignition system 3. Fuel system 4. Intake/exhaust air system 5. Ignition timing 6. Injector | |
Case1 | Enable Conditions |
•
400 rpm ＜ Engine speed ＜ 4520rpm
•
Engine load > Zero torque line | |
Threshold Value |
•
Misfire rate > 3.25% per 1000 rev. | ||
MIL ON Condition |
•
3 driving cycle | ||
Case2 | Enable Conditions |
•
Intake air temperature > -8.3℃
•
Coolant temperature > -8.3℃ | |
Threshold Value |
•
Misfire rate > 2.5~22.2% per 200 rev. (Depends on driving conditions) | ||
MIL ON Condition |
•
Immediately (Blink) | ||
