Jeep Grand Cherokee WK. Manual — part 934
P0302-CYLINDER 2 MISFIRE (CONTINUED)
For the Engine circuit diagram (Refer to 9 - ENGINE - SCHEMATICS AND DIAGRAMS).
For a complete wiring diagram Refer to Section 8W.
•
When Monitored:
Any time the engine is running, and the adaptive numerator has been successfully updated.
•
Set Condition:
When more than 2% (2.5% LEV) misfire rate is measured during two trips, or with 10 % to 30 % misfire rate
during one trip. Three good trips to clear the MIL.
Possible Causes
(F42), (A15) ASD RELAY OUTPUT CIRCUIT
(K12) INJECTOR CONTROL NO.2 CIRCUIT
(K85) COIL CONTROL NO.2 CIRCUIT
IGNITION WIRE
SPARK PLUG
IGNITION COIL
FUEL PUMP INLET STRAINER PLUGGED
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP MODULE
FUEL PRESSURE LEAK DOWN
FUEL INJECTOR
ENGINE MECHANICAL
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.
CYLINDER MIS-FIRE CONDITION ACTIVE
Engine running.
Observe the WHICH CYLINDER IS MISFIRING screen for at least one minute with the scan tool.
Is there a misfire present?
Yes
>> Go To 2
No
>> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
WK
P0302-CYLINDER 2 MISFIRE (CONTINUED)
2.
VISUAL INSPECTION
NOTE: Anything that affects the speed of the crankshaft can cause a misfire DTC.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinders Injector
Control circuit.
- Visually inspect the engine for any of the following conditions.
- Worn serpentine belt
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment of the Water pump, P/S Pump and A/C Compressor pulleys
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP, and TP Sensor mounting
- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector, Ign coil, etc.
- Vacuum leaks
- Restricted Air Induction system or Exhaust system.
- Internal engine component failures.
Were any of the above conditions present?
Yes
>> Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 3
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ENGINE ELECTRICAL DIAGNOSTICS
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P0302-CYLINDER 2 MISFIRE (CONTINUED)
3.
(F42), (A15) ASD RELAY OUTPUT CIRCUIT
Turn the ignition off.
Disconnect the Ignition Coil No.2 harness connector.
Disconnect the Fuel Injector No.2 harness connector.
Ignition on, engine not running.
With the scan tool, actuate the ASD Relay.
Using a 12-volt test light connected to ground, probe the (F42), (A15)
ASD Relay Output circuit in the Ignition Coil harness connector and
Fuel Injector harness connector while the relay is actuating.
Does the test light illuminate brightly?
Yes
>> Go To 4
No
>> Repair the excessive resistance or short to ground in the
(F42), (A15) ASD Relay Output circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer
to 9 - ENGINE - STANDARD PROCEDURE)
4.
IGNITION SYSTEM OPERATION
Turn the ignition off.
Connect the Ignition Coil No.2 harness connector.
Remove the Ignition Coil.
Leave the Fuel Injector harness connector of the cylinder being tested disconnected.
Install a spark tester on the Ignition Coil.
While cranking the engine observe the spark coming from the spark tester.
NOTE: A crisp blue spark that is able to jump the gap of the spark tester should be generated.
Is good spark present?
Yes
>> Go To 5
No
>> Go To 14
NOTE: Connect the Fuel Injector harness connector before continuing.
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P0302-CYLINDER 2 MISFIRE (CONTINUED)
5.
SPARK PLUG
Turn the ignition off.
Remove the Spark Plug.
Inspect the Spark Plug for the following conditions.
- Cracks
- Carbon Tracking
- Foreign Material
- Gap size out of specifications
- Loose or broke electrode
NOTE: Lightly tap the bottom of the spark plug on a solid surface. The electrode in the spark plug should
not move.
Were any of the above conditions present?
Yes
>> Replace the Spark Plug.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 6
6.
FUEL PRESSURE CHECK
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or ser-
vicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow
these instructions can result in personal injury or death.
Install a fuel pressure gauge to the fuel rail.
Start the engine and observe the fuel pressure reading.
NOTE: Fuel pressure specification is 407 KPa +/- 34 KPa (59 psi +/- 5 psi).
Choose a conclusion that best matches your fuel pressure reading.
Within Specification
Go To 7
Below Specification
Go To 12
Above Specification
Replace the fuel filter/pressure regulator.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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