Component Location
General Description
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.
DTC Description
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.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | Calculation of engine roughness
| Faulty spark plugs, high-tension lead, or Ignition coil
Incorrect valve timing
Uneven compression
Air leakage
Improper Fuel pressure or dirty fuel.
Blocked/Leaking injectors
Leakage between cooling system and cylinder
|
Enable Conditions | 156 < Mass air flow(mg/rev.) < 710 (depends on RPM , Coolant temp.)
512 < Engine speed(RPM) < 6500
141 < Throttle gradient(°TPS/sec.) < 199
Coolant temperature > 20°C (-4?) if Start temperature < -7°C (19.4?)
No rough road
No relevant failure
11V< Battery voltage
Fuel cut off not active
|
Threshold Value | Case1 | Misfire = 12~54% within 200 rev.(Catalyst temperature >1050°C (1922?))
|
Case2 | Misfire = 3.5% within 1000 rev.
|
Diagnosis Time | Case1 | 200 revolution or 3*200 revolution
|
Case2 | 1000 revolution or 4*1000 revolution
|
Mil On Condition | Case1 | Immediate
|
Case2 | 2 Driving Cycles
|
Specification
Temp.(?) | Temp.(?) | Primary ignition coil (?) | Secondary ignition coil(?) |
20 | 68 | 0.5~0.6 | 7.5~10.2 |