Description
Misfire Monitoring Description
1. Fault Code:
Individual fault codes for each cylinder, for either excess emissions or catalyst damage and corresponding multiple cylinder codes.
Catalyst Damage Bank A Misfire Fault P1313
Catalyst Damage Bank B Misfire Fault P1314
Excess Emissions Misfire Fault P1316
Random / Multiple Misfire P0300
Misfire Detected - Cyl 1 P0301
Misfire Detected - Cyl 2 P0302
Misfire Detected - Cyl 3 P0303
Misfire Detected - Cyl 4 P0304
Misfire Detected - Cyl 5 P0305
Misfire Detected - Cyl 6 P0306
Misfire Detected - Cyl 7 P0307
Misfire Detected - Cyl 8 P0308
2. Monitoring Procedure
Misfire detection using crankshaft period measurements has been implemented. Two algorithms compare changes in crankshaft period with respective threshold values that are speed and load dependant. If the change in crankshaft period exceeds the threshold value a misfire has occurred.
Percentage misfire is calculated over 200 or 1000 engine revolution blocks for each bank of cylinders and compared to threshold levels for excess emissions or catalyst damage. Whenever conditions are not suitable for misfire detection, engine revolution counting and misfire counting is suspended. When conditions are suitable, counting continues from the last updated values.
Catalyst Damage
The total percentage misfire indicated by the algorithm is calculated in blocks of 200 revolutions of the crankshaft. If this value exceeds the misfire rate that indicates catalyst damage (MF DIAG THRESH PCENT MF CAT), cylinder identification takes place and a misfire catalyst damage fault is present for the appropriate bank.
Excess Emissions
The percentage misfire (MF DIAG PCENT MF EMISS) is calculated in blocks of 1000 revolutions of the crankshaft using MF DIAG FIRE COUNT EMISS I as the revolution count. If the misfire rate is high enough to exceed specified emission limits, cylinder identification takes place and a misfire emission fault is present.
Cylinder Identification
Each misfire detected will be referenced to a particular cylinder.
If the number of misfires occurring on a particular cylinder exceeds a given percentage of the total number of misfires from all the cylinders, then that cylinder is considered to be misfiring and a misfire cylinder number (1 to 8 cyl) fault is present.
Otherwise a misfire on multiple cylinders fault is present.
3. Primary Detection Parameter
Crankshaft speed changes processed over a series of engine firings.
4. Fault Criteria Limits
Misfire to exceed emissions limit - 2%
Misfire to cause catalyst damage - 15%
5. Monitoring Conditions
The engine must be stabilized after any rapid throttle excursion, fuel cut off condition or gear change. Monitoring is disabled during rough road conditions.
The engine load must exceed a threshold, which is mapped with engine speed (to represent the positive/negative engine torque boundary).
6. Monitoring Time Length / Frequency of Checks
The misfire percentage is checked at the end of every block of 200 or 1000 engine revolutions as required. The counting of engine revolutions is suspended during engine stabilization as described above.
7. Criteria for Storing Fault Code
If catalyst damage levels of misfire are detected the fault code is stored immediately.
If misfire above the emission threshold (only) is detected, then a set of conditions is stored. A fault code will be stored if misfire is detected on a subsequent driving cycle while the conditions are still stored. The conditions can be erased on intervening fault free driving cycles as allowed in OBD II regulations.
8. Criteria for Illuminating MIL
If catalyst damage levels of misfire are detected the MIL will be flashed for as long as the catalyst damage misfire level is present.
If misfire above the emission threshold (only) is detected, then a set of conditions is stored. The MIL will be illuminated if misfire is detected on a subsequent driving cycle while the conditions are still stored. The conditions can be erased on intervening fault free driving cycles as allowed in OBD II regulations.
9. Criteria for Determining Out of Range Input Signals
The crankshaft position sensing system is subject to diagnostics, which detect more or less than the correct number of sensor transitions per engine revolution.