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 two 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 change 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 vlotage〈 16 ● TPS/MAP sensor/CAMS/CKPS/ECT sensor are normal | ||
Thresh old value | Case 1 | ● Individual event misfire detection 〉 Threshold | |
Case 2 | ● Emissions damaging 〉Threshold | ||
Case 3 | ● Catalyst damaging 〉 Threshold | ||
Diagnosis time | ● Continuous | ||
MIL ON condition | ● 2 driving cycles | ||
Is the power balance test done?
▶ If injector connector for power balance test is disconnect for over 46 sec., this can cause DTC relating to misfire. Stop the test and connect it and delete DTC and then go to "Verification of Vehicle repair" procedure.
▶ If power balance test is finished within 46 sec., go to next procedure.
▶ Go to "Monitor scantool data" as follows.
Monitor scantool data
Ignition "OFF"
Connect Scantool and Engine "ON"
Monitor parameters related to " Cylinder 4 Misfire Detected" on CURRENT DATA
Ignition | BTDC 10° ± 5° | |||
Idle speed | N-range | 720 ± 100 rpm | ||
D-range | 650 ± 100 rpm | |||
Are the parameters related to "Cylinder 4 Misfire Detected" displayed correctly on Current Data ?
▶ Fault is intermittent caused by poor contact in the sensor’s and/or PCM’s connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
▶ Go to "System Inspection " procedure
Check Spark Pulg
Remove cylinder’s spark plugs
Visually/physically inspect the following items:
- Damaged insulation, Worn electrodes, Oil or fuel fouled, Loose terminals and cracks
- Check for plug gap : 1.0 - 1.1 mm (0.039 - 0.043 in.)
- Check if the spark plug for the relevant cylinder is lighter in color than the other plugs.
Has a problem been found in any of the above areas?
▶ Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
▶ Go to "Check Air Leakage " as below
Check Air Leakage
Visually/physically inspect the air leakage in intake/exhaust system as following items,
- Vacuum hoses for splits, kinks and improper connections.
- Throttle body gasket
- Gasket between intake manifold and cylinder head
- Seals between intake manifold and fuel injectors
- Exhaust system between HO2S and Three way catalyst for air leakage
Has a problem been found in any of the above areas?
▶ Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
▶ Go to "Check for air leakage in Positive Crankcase Ventilation Valve(PCV)
Check for air leakage in Positive Crankcase Ventilation Valve(PCV)
Remove PCV valve from cylinder head cover by puling ventilation hose
With engine idling block PCV valve opening
Verify that vacuum is felt
Remove PCV valve
Blow through valve from prot "A" and verify that air comes out of prot "B"
Blow through valve from prot "B" and verifty that no air comes out of port "A"
Has a problem been found ?
▶ Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
▶ Go to "Check Compression pressure" as below
Check Compression pressure
Warm up the engine to normal operating temperature
Disconnect the spark plug cables and remove the spark plugs.
Crank the engine to remove any foreign material in the cylinders.
Put compression pressure gauge into spark pulg hole
Crank the engine with widely opend throttle valve and check compression pressure at each cylinder
Specification : 1323kPa(13.5 kg/cm²,192 psi)
Is compression pressure for each cylinder displayed within specifications ?
▶ Go to "Check Timing " as below
▶ Add a small amount of oil through the spark plug hole, and repeat above steps. If the addition of oil causes the compression to rise, the cause is a worn or damaged piston ring or cylinder inner surface.
▶ If the compression remains the same, the cause is a burnt or defective valve seat, or pressure is leaking from the gasket. Repair as necessary and go to "Verification of Vehicle Repair" procedure
Check Timing
Ignition "OFF"
Check that Cam, Crank and Oil pump sprocket timing marks are correctly in alignment
Monitor these signal waveforms from CAM and Crank shaft position Sensor are correctly in alignment
Are all timing marks alligned correctly ?
▶ Go to "Check Fuel Pressure Test" as below
▶ Repair or readjust as necessary and go to "Verification of Vehicle Repair" procedure
Check Fuel Pressure Test
Refer to "Fuel pressure test" in "Fuel delivery system"
Are the measured fuel pressure within specifications ?
▶ Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
There is a memory reset function on scantool that can erase optional parts automatically detected and memorized by PCM. After testing PCM on the vehicle, use this function to reuse the PCM on the others
▶ Repair or replace as necessary above and then, go to " Verification of Vehicle Repair"procedure.
After a repair, it is essential to verify that the fault has been corrected.
Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code(DTC) which has been diagnosed.
Using a Scantool, Clear the DTCs
Operate the vehicle within conditions noted in the freeze frame data or enable conditions
Monitor that all rediness test have been verified as " Complete "
Are any DTCs present ?
▶ Go to the applicable troubleshoooting procedure.
▶ System is performing to specification at this time.
