Jeep XJ. Manual — part 834
Symptom List:
P0300-MULTIPLE CYLINDER MIS-FIRE
P0301-CYLINDER #1 MISFIRE
P0302-CYLINDER #2 MISFIRE
P0303-CYLINDER #3 MISFIRE
P0304-CYLINDER #4 MISFIRE
P0305-CYLINDER #5 MISFIRE
P0306-CYLINDER #6 MISFIRE
Test Note:
All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P0300-MULTIPLE CYLINDER
MIS-FIRE.
When Monitored and Set Condition:
P0300-MULTIPLE CYLINDER MIS-FIRE
When Monitored:
Any time the engine is running, and the adaptive numerator has been
successfully updated.
Set Condition:
When more than a 2% (1.5% LEV) misfire rate is measured during two
trips (one trip California), or with a 10% to 30% misfire rate during one trip.
P0301-CYLINDER #1 MISFIRE
When Monitored:
Any time the engine is running, and the adaptive numerator has been
successfully updated.
Set Condition:
When more than a 2% (1.5% LEV) misfire rate is measured during two
trips (one trip California), or with a 10% to 30% misfire rate during one trip.
P0302-CYLINDER #2 MISFIRE
When Monitored:
Any time the engine is running, and the adaptive numerator has been
successfully updated.
Set Condition:
When more than a 2% (1.5% LEV) misfire rate is measured during two
trips (one trip California), or with a 10% to 30% misfire rate during one trip..
P0303-CYLINDER #3 MISFIRE
When Monitored:
Any time the engine is running, and the adaptive numerator has been
successfully updated.
Set Condition:
When more than a 2% (1.5% LEV) misfire rate is measured during two
trips (one trip California), or with a 10% to 30% misfire rate during one trip.
P0304-CYLINDER #4 MISFIRE
When Monitored:
Any time the engine is running, and the adaptive numerator has been
successfully updated.
Set Condition:
When more than a 2% (1.5% LEV) misfire rate is measured during two
trips (one trip California), or with a 10% to 30% misfire rate during one trip.
97
DRIVEABILITY - GAS
P0305-CYLINDER #5 MISFIRE
When Monitored:
Any time the engine is running, and the adaptive numerator has been
successfully updated.
Set Condition:
When more than a 2% (1.5% LEV) misfire rate is measured during two
trips (one trip California), or with a 10% to 30% misfire rate during one trip..
P0306-CYLINDER #6 MISFIRE
When Monitored:
Any time the engine is running, and the adaptive numerator has been
successfully updated.
Set Condition:
When more than a 2% (1.5% LEV) misfire rate is measured during two
trips (one trip California), or with a 10% to 30% misfire rate during one trip.
POSSIBLE CAUSES
ENGINE MECHANICAL PROBLEM
ERRATIC CAM/CRANK SENSOR SIGNALS
FUEL SYSTEM PROBLEM
MIS-FIRE CONDITIONS NO LONGER EXIST
OTHER POSSIBLE CAUSES FOR MIS-FIRE
SECONDARY IGNITION OR MECHANICAL PROBLEM
TEST
ACTION
APPLICABILITY
1
Note: Repair all other PCM DTC’s before continuing with this test.
With the DRBIII
t, read DTC’s.
Is the MIS-FIRE GOOD TRIP counter displayed and equal to zero?
All
Yes
→
No
→
2
At this time the conditions that set the Misfire DTC are present.
With the DRBIII
t, select DTC’s and RELATED FUNCTIONS. Read and record the
FREEZE FRAME DATA. Select OBD II MONITORS. Read and record the MIS-FIRE
SIMILAR CONDITIONS WINDOW DATA.
With these screens, attempt to duplicate the condition(s) that has set this DTC.
When the vehicle is operating in the SIMILAR CONDITIONS WINDOW, refer to the
WHICH CYLINDER IS MISFIRING screen.
Observe the WHICH CYLINDER IS MISFIRING screen for at least one minute.
Is the DRBIII
t counting mis-fires at this time?
All
Yes
→
No
→
Test Complete.
98
DRIVEABILITY - GAS
P0300-MULTIPLE CYLINDER MIS-FIRE —
Continued
TEST
ACTION
APPLICABILITY
3
With the DRBIII
t, read the FREEZE FRAME DATA.
Use the FREEZE FRAME DATA and attempt to determine the cause of the Misfire
DTC.
In the FREEZE FRAME, are the adaptive fuel percentages greater than +/- 15%?
All
Yes
→
Refer to the Driveablitiy Category and perform the Checking Fuel
Delivery symptom.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST.
No
→
4
At this time the mis-fire does not exist or is an intermittent problem.
Note: An intermittent problem may have been caused by moisture in the
secondary ignition.
With the DRBIII
t, select DTC’s AND RELATED FUNCTIONS. Read and record the
FREEZE FRAME DATA. Select OBD II MONITORS. Read and record MIS-FIRE
SIMILAR CONDITIONS WINDOW DATA.
With these screens, attempt to duplicate the condition that has set the Misfire DTC.
While using FREEZE FRAME DATA, pay particular attention to the DTC setting
conditions, such as speed, temp, load, and map vacuum.
Does the mis-fire recur?
All
Yes
→
No
→
Test Complete.
5
With the DRBIII
t, read the FREEZE FRAME DATA.
Use the FREEZE FRAME DATA and attempt to determine the cause of the Misfire
DTC.
In the FREEZE FRAME, are the adaptive fuel percentages greater than +/- 15%?
All
Yes
→
Refer to the Driveablitiy Category and perform the Checking Fuel
Delivery symptom.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST.
No
→
6
With the DRBIII
t, read the FREEZE FRAME DATA.
Use the FREEZE FRAME DATA and attempt to determine the cause of the Misfire
DTC.
In the FREEZE FRAME DATA, is the engine RPM over 3000 and the operating temp
normal?
All
Yes
→
Test CMP and CKP signals with Lab Scope, check valve timing,
and perform running vacuum test.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST.
No
→
99
DRIVEABILITY - GAS
P0300-MULTIPLE CYLINDER MIS-FIRE —
Continued
TEST
ACTION
APPLICABILITY
7
Check for any of the following conditions/mechanical problems.
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
FUEL INJECTOR - plugged or restricted injector; control wire not connected to
correct injector
Are there any engine mechanical problems?
All
Yes
→
Repair as necessary.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST.
No
→
8
With the DRBIII
t, read the FREEZE FRAME DATA.
Use the FREEZE FRAME DATA and attempt to determine the cause of the Misfire
DTC.
In the FREEZE FRAME DATA, is the LOAD VALUE over 50% and the operating
temp normal?
All
Yes
→
Check secondary ignition, compression, and cylinder leakage.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST.
No
→
9
Note: Anything that affects the speed of the crankshaft can cause a misfire
DTC.
The following are other possible causes for mis-fire:
Injector harness connectors, secondary ignition problem, mechanical engine problem,
PCM power grounds, irregular cam and crank signal, plugged injectors, restricted
exhaust, intake restriction, damaged trigger wheel, contaminated fuel, or vacuum
leak.
Weak valve springs, carbon deposits on valves, or accessory drive belt (serpentine
belt).
Check for any TSB’s that may relate to a Misfire DTC.
Do any of the above causes exist?
All
Yes
→
Repair as necessary.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST.
No
→
Test Complete.
100
DRIVEABILITY - GAS
P0300-MULTIPLE CYLINDER MIS-FIRE —
Continued
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