Component Location
Description
1. General Description
The Misfire monitor diagnostic is based on crankshaft rotation velocity variation. The ECM 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 ECM 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 ECM 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 ECM uses the signal to distinguish the phenomenon from actual misfiring.
2. DTC Description
The ECM must monitor the engine for misfiring possibly caused by ignition coil defects or injector fails. If misfiring is detected, the ECM will identify the cylinder(s) that has(have) misfired and then calculate misfiring rate for a given duration. The DTC for Misfire (P0301 to 0304) is set as soon as the misfiring rate exceeds the limit which may result in damage to the catalyst or increase emissions. The ECM stores the individual DTC for a cylinder which has more than a 10% total misfire rate. With a more than two cylinder misfire detection, the ECM sets P0306.
When an extremely high misfire rate occurs, which has a danger of burning up the catalyst, the MIL blinks immediately.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | ? Calculation of engine roughness | ? Defective 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 | ? After starting ? Mass air flow > Approx. 0 ? 550< Engine speed(RPM)< 6500 ? Intake air mass gradient is in predetermined range ? Throttle Angle gradient is in predetermined range ? No injector shut off ? No rough road |
Case1) | Threshold Value | ? Misfire= 6~17% within 200 rev. |
Diagnosis Time | ? 200 revolution: 3*200 revolution |
Case2) | Threshold Value | ? First 1000 rev.: Misfire >2% ? After first 1000 rev.: Misfire >2% |
Diagnosis Time | ? 1000 revolution: 4*1000 revolution |
Fail Safe | ? EVAP. Emission control function is controlled in minimum operation mode ? Injection shut-off |
Schematic Diagram