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 PCM monitors the crankshaft speed variation to determine if any misfiring generated. The PCM 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.
The PCM measures reference event times and calculates the positive and negative acceleration of the crank wheel to detrmine whether a misfire has occurred.
When the rate of misfire exceeds a threshold where the catalyst reaches a temperature where permanent damage can ocur. PCM sets this DTC. In case that misfire affects Catalyst damage, MIL(Malfunction Indication Lamp) will be illuminating and blinking at 1HZ frequency. However, In case of Indivisual and Emission damaging misfire, MIL will be turned on when the malfunction is detected.
Especially, if injector connector is disconnected for more than 46 sec., PCM sets DTC relating to misfire and conducts the fuel-cut to protect the catalyst.
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Determine if a multiple cylinder misfire or a cylinder specific misfire is occurring by monitoring crankshaft acceleration. | ● Faulty Spark plugs ● Faulty Spark plug cables ● Air Leakage ● Belt deflection and Air gap of CKPS ● Incorrect timing ● Faulty injector ● Improper fuel pressure ● Improper engine compression ● Faulty PCM |
Enable Condition | ● No sudden changd in throttle opening ● Torque management control is not functioning ● Not deceleration fuel cut-off ● Not fuel cut-off during high speed operation ● Not negative torque driving conditions ● Not fuel level low ● TEC is learned ● Coolant temperature is outside the window ● 500 ＜ Engine speed ＜ 6600 ● 11 ＜ Battery voltage ＜ 16 ● TPS ＜ MAP sensor ＜ CAMS ＜ CKPS ＜ ECT sensor are normal | |
Threshold Value | Case1 | ● Individual event misfire detection > Threshold |
Case2 | ● Emissions damaging >Threshold | |
Case3 | ● Catalyst damaging > Threshold | |
Diagnosis Time | ● Continuous | |
MIL On Condition | ● 2 driving cycles |
