The Misfire monitor diagnostic is based on crankshaft rotation velocity variation. The PCM determines crankshaft rotational velocity using the crankshaft position sensor and camshaft position sensor. When a cylinder misfires the crankshaft slows down momentarily. By monitoring the crankshaft and camshaft position sensor signals, the PCM can calculate when a misfire occurs. For a non-catalyst damaging misfire, the diagnostic will be required to report a misfire present within 1000-3200 engine revolutions. For catalyst damaging misfire, the diagnostic will respond to monitor 200 engine revolutions. Rough roads may cause false misfire detection. The rough road(acceleration)sensor consists of a piezoelectric vibration pick up which detects vertical acceleration of the vehicle. The sensor signal is used by the PCM to determine the degree of vertical movement of the car, for example, on a bumpy road. Since this may also cause uneven engine running, the PCM uses the signal to distinguish the phenomenon from actual misfiring.
If the PCM detects that engine speed variation indicates a misfire sufficient to cause three-way catalyst converter damage or emissions level to exceed standard value, the PCM sets DTC P0302. If the misfire rate is high enough to damage the catalyst, the MIL will flash to alert the vehicle operator.
Item | Detecting Condition | Possible Cause | |
DTC Strategy |
•
Calculation of engine roughness | 1. Faulty spark plugs or Ignition coil 2. Incorrect valve timing 3. Uneven compression 4. Air leakage 5. Improper Fuel pressure or dirty fuel. 6. Blocked/Leaking injectors 7. Leakage between cooling system and cylinder | |
Enable Conditions |
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Engine load ratio : 14~64%
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500< Engine speed(rpm) <6700
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Mass air flow gradient/sec. : 12~60%
•
Throttle gradient/sec. : 58.6~1265.6%
•
Coolant temperature >20℃(68℉) if start temp. <-7℃(19℉)
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No relevant failure
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Fuel cut-off not active
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11V< Battery voltage <16V | ||
Threshold Value | Case1 |
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Misfire ratio :10 ~ 50% within 200 rev. | |
Case2 |
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Misfire ratio :2.0% within 1,000 rev. | ||
Diagnosis Time | Case1 |
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200 rev | |
Case2 |
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1000 rev | ||
MIL On Condition | Case1 |
•
Immediate | |
Case2 |
•
2 Driving Cycles | ||
Temp.(℃) | Temp.(℉) | Primary ignition coil (Ω) | Secondary ignition coil(㏀) |
20 | 68 | 0.56~0.68 | 6~8 |
