GENERAL DESCRIPTION |
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 fuel mixture. Increased misfire rates will cause damage to the catalytic converter. The ECM monitors the crankshaft speed variation to determine if misfires occur. 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.
DTC DESCRIPTION |
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.
DTC DETECTING CONDITION |
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Item | Detecting Condition | Possible Cause | |||||||||||||||||||
DTC Strategy |
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Enable Conditions | No disabling faults present / no disabiling Active Faults
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Threshold value | Case 1 |
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Case 2 |
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Case 3 |
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Diagnosis Time |
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MIL On Condition |
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SIGNAL WAVEFORM & DATA |
Fig.1) Normal data of misfire counter at idle.
Fig.2) Abnormal data of misfire counter when cyliner 4 injector open.
MONITOR GDS DATA |
1. | Connect GDS to Data Link Connector(DLC). |
2. | IG “ON”. |
3. | Select “DTC” button, and then Press “DTC Status” to check DTC’s information from the DTCs menu. |
4. | Read “DTC Status” parameter. |
5. | Is parameter displayed “Present fault”? Â
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SYSTEM INSPECTION |
â– Misfire Inspection |
1. | Check the cylinder where the misfire occurs after replacing the ignition coil of the cylinder where the misfire has occurred with the ignition coil of the other cylinder. |
2. | Does the misfiring cylinder change? Â
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â– Ignition coil waveform inspection |
1. | Ignition “ON” and engine “ON”. |
2. | Measure the voltage between control terminal of ignition soil harness connector and chassis ground.
Fig.1) Engine Idle after Warm Up Spark retention time – Approx. 1.2ms CH. A – Ignition Max 31V |
3. | Is the measured waveform within specification? Â
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â– Check Spark Pulg |
1. | Remove cylinder’s spark plugs. |
2. | Visually/physically inspect the following items: â–¶ Damaged insulation, Worn electrodes, Oil or fuel fouled, Loose terminals and cracks. â–¶ Check for plug gap : 1.0 – 1.1 mm (0.039 – 0.043 in.) â–¶ Check if the spark plug for the relevant cylinder is lighter in color than the other plugs. |
3. | Has a problem been found in any of the above areas? Â
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â– Check Air Leakage |
1. | Visually/physically inspect the air leakage in intake/exhaust system as following items, â–¶ Vacuum hoses for splits, kinks and improper connections. â–¶ Throttle body gasket. â–¶ Gasket between intake manifold and cylinder head. â–¶ Seals between intake manifold and fuel injectors. â–¶ Exhaust system between HO2S and Three way catalyst for air leakage. |
2. | Has a problem been found in any of the above areas? Â
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â– Check for air leakage in Positive Crankcase Ventilation Valve(PCV) |
1. | Remove PCV valve from cylinder head cover by puling ventilation hose. |
2. | With engine idling block PCV valve opening. |
3. | Verify that vacuum is felt. |
4. | Remove PCV valve. |
5. | Blow through valve from prot “A” and verify that air comes out of prot “B”. |
6. | Blow through valve from prot “B” and verifty that no air comes out of port “A”. |
7. | Has a problem been found in any of the above areas? Â
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â– Check Compression pressure |
1. | Warm up the engine to normal operating temperature. |
2. | Disconnect the spark plug cables and remove the spark plugs. |
3. | Crank the engine to remove any foreign material in the cylinders. |
4. | Put compression pressure gauge into spark pulg hole. |
5. | Crank the engine with widely opend throttle valve and check compression pressure at each cylinder.
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6. | Is compression pressure for each cylinder displayed within specifications ? Â
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â– Check Timing |
1. | IG “OFF” |
2. | Monitor these signal waveforms from CAM and Crank shaft position Sensor are correctly aligned. Reference : The 17th of CKP signal from missing tooth is aligned with high of CMP signal. |
3. | Are all timing marks alligned correctly ? Â
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â– Check fuel pressure |
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1. | IG “OFF” and disconnect Fuel Pump Relay in Junction Box. |
2. | Start-up and wait until it stops itself. |
3. | IG “OFF” and connect Fuel Pump Relay. |
4. | Install the fuel pressure gauge to the delivery pipe with the fuel pressure gauge adaptor. |
5. | Activate the fuel pump, and with fuel pressure applied, check that there is no fuel leakage from the pressure gauge or connection part. |
6. | Measure the fuel pressure at idle.
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7. | Is the measured fuel pressure within specifications ? Â
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