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 two or more cylinders are misfiring.
The ECM 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, to the point that tail pipe emissions reach 1.5 times the tailpipe standard or where a cylinder misfire cause a loss of torque produced from that cylinder.
ECM sets this DTC. In case that misfire affects Catalyst damage, MIL(Malfunction Indicatin 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.
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
Enable Conditions
No disabling faults present / no disabiling Active Faults
P0340 / P0341 / P0118 / P0117 / P0115 / P0336 / P0335 / P1295 / P0103 / P0102 / 0108 / P0107 / P0106 / P0501
Engine speed between 550 and 5800 RPM
System voltage between 9 and 18 volts
The ECT indicates an engine temperature between -6?(20?) and 120?(248?)
Threshold value
Case 1
Individual cylinder misfire detection
Case 2
Emissions damaging - 18 times in 600 ignitions
(In case that the misfire affects more than 1.5 times than FTP emissins)
Case 3
Catalyst damaging - 95 times in 600 ignitions at idle
( It is going to be changeable according to the load or the temperature which is not in the range where it does not melt catalyst)
Diagnosis Time
Continuous
MIL On Condition
2 Driving Cycles
Fig.1) Normal data of misfire counter at idle.
Fig.2) Abnormal data of misfire counter when cyliner 2 injector open.