P0304
P0304-CYLINDER 4 MISFIRE
Special Tools:
For a complete wiring diagram, refer to the Wiring Information.
Theory of operation
The misfire detection monitor, software strategy in the Powertrain Control Module (PCM), is designed to detect an engine misfire. The PCM uses the Crankshaft (CKP) and Camshaft (CMP) sensors to determine when an engine misfire event is occurring and determine individual misfire events by monitoring the crankshaft rotational speed. A misfire is nothing more than a lack of combustion, which can be caused by poor fuel quality or metering, low compression, lack of spark or unmetered air entering the engine. Other possible causes such as uncommanded Exhaust Gas Recirculation (EGR) flow can also cause a misfire. In the case of multiple cylinders misfiring, or the PCM not determining the specific cylinder misfiring, P0300 Multiple Cylinder Misfire will set.
- When Monitored:
Any time the engine is running, and the adaptive numerator has been successfully updated.
- Set Condition:
The threshold to set the fault is application specific; it is tied to the level of misfire that will cause emissions to increase to 1.5 times the standard or in some cases 1%. It is always a two trip fault above the calibrated RPM. It takes one fail to set a Pending Fault and two trips to set the MIL. Three good trips to turn off the MIL.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
1. ACTIVE DTC
1. Diagnose and repair any other active component or circuit DTCs before continuing with this procedure.
2. Turn the ignition on.
3. With the scan tool, select View DTCs. Copy DTC and Freeze Frame information.
4. Operate the vehicle under conditions similar to which the DTC was set.
5. With the scan tool, view the Misfire Monitor to see which cylinders are effected.
NOTE: It may be necessary to test drive the vehicle within the DTC monitoring conditions in order for this DTC to set or to show misfires on a particular cylinder.
Are there excessive misfires shown or is the DTC pending at this time?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test
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 cylinder's Injector Control circuit.
NOTE: Misfires detected during a deceleration are indicators of mechanical concerns.
Visually inspect the engine for any of the following conditions:
- Worn serpentine belt. Testing and Inspection.
- 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 for CKP sensor, CMP sensor, MAP sensor, TP sensor, fuel injector, ignition coil, etc.
- Vacuum leaks.
- Restricted Exhaust system. Perform the CHECKING EXHAUST RESTRICTION diagnostic procedure. .
- Restricted Air Induction system.
- Internal engine component failures.
- Overfilled engine oil or transmission.
- Extremely out of balance tires or warped brake rotors.
Were any of the above conditions present?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 3
3. IGNITION SYSTEM OPERATION
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
1. Turn the ignition off.
2. Remove the Ignition Coils.
3. Connect the Ignition Coil harness connectors.
4. Disconnect the Fuel Injector harness connector of the cylinder being tested.
5. Install a spark tester on the Ignition Coil.
6. 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 at the coil on plug and at the end of the ignition wire.
Is good spark present?
Yes
- Go To 4
No
- Go To 13
NOTE: Connect the Fuel Injector harness connector before continuing.
4. SPARK PLUG
1. Turn the ignition off.
2. Remove the Spark Plug(s). Spark Plug - Removal
3. Inspect the Spark Plug(s) for the following conditions:
- Cracks
- Carbon Tracking
- Foreign Material
- Gap size out of specifications
- Loose or broken 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. Spark Plug - Removal
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 5
5. FUEL PRESSURE CHECK
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in possible serious or fatal injury.
NOTE: Before continuing, visually and physically inspect the fuel delivery system for external leaks or damage. Repair/replace as necessary.
1. Install the Fuel Pressure Decay Tester to the fuel rail.
2. Start the engine and observe the fuel pressure reading.
NOTE: Fuel pressure specification is 400 kPa +/- 14 kPa (58 psi +/- 2 psi).
Choose a conclusion that best matches your fuel pressure reading.
Within Specification
- Go To 6
Below Specification
- Go To 11
Above Specification
- Replace the fuel pressure regulator. Fuel Tank - Removal
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
6. FUEL PRESSURE LEAK DOWN
1. Perform the Fuel Pressure Leak Down Test. Fuel Pressure Leak Down
Were any repairs made after performing the leak down test?
Yes
- Testing complete.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 7
7. FUEL INJECTOR OPERATION
CAUTION: After each Fuel Injector actuation, start the engine to clean the cylinder of fuel. Failure to do so could cause engine damage.
1. Open the Fuel System Isolation Valve.
2. Start the engine and allow the fuel pressure to reach maximum pressure.
3. Turn the ignition off.
4. Ignition on, engine not running.
5. Using the scan tool, actuate the Fuel Injector for the cylinder that indicated the misfire.
6. Monitor the fuel pressure gauge.
Does the fuel pressure gauge indicate a drop in fuel pressure?
Yes
- Go To 8
No
- Go To 9
NOTE: Turn the ignition off, remove the Fuel Pressure Decay Tester and connect the fuel lines before continuing.
8. ENGINE MECHANICAL
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
- CYLINDER LEAKAGE TEST - 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
- VALVE SPRINGS - cannot be weak or broken
- CAM LOBES - must not be worn excessively
- CAM SHAFTS - must not be worn or have excessive endplay
Are there any engine mechanical problems?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 17
9. FUEL INJECTOR CONTROL
1. Turn the ignition off.
2. Disconnect the Fuel Injector harness connector of the misfiring cylinder.
3. Ignition on, engine not running.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinder's Injector Control circuit.
4. Install an Injector Noid light.
5. With the scan tool, actuate the Fuel Injector.
Does the Noid light blink/flicker during the actuation?
Yes
- Verify that there is good pin to terminal contact in the related Injector and the Powertrain Control Module connectors. Replace the Fuel Injector. Fuel Injector - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 10
10. INJECTOR CONTROL CIRCUIT
1. Turn the ignition off.
2. Remove the Injector Noid light.
3. Disconnect the PCM C2 harness connector.
4. Check the Injector Control circuit for an open, short to ground and short to voltage.
Was a problem found with the Injector Control circuit?
Yes
- Repair the excessive resistance or short in the Injector Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 17
11. FUEL SUPPLY LINE RESTRICTED
1. Turn the ignition off.
2. Raise the vehicle on a hoist and disconnect the fuel pressure line at the fuel pump module.
3. Install the Fuel Pressure Decay Tester between the fuel supply line and the fuel pump module.
4. Ignition on, engine not running.
5. With the scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.
NOTE: Fuel pressure specification is 400 kPa +/- 14 kPa (58 psi +/- 2 psi).
Is the fuel pressure within specification?
Yes
- Repair or replace fuel supply line as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 12
12. FUEL PUMP INLET STRAINER
1. Turn the ignition off.
2. Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer. Fuel Tank - Removal.
Is the Fuel Inlet Strainer plugged?
Yes
- Replace the Fuel Pump Inlet Strainer. Fuel Tank - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Before continuing, check the Fuel Pump Module harness connector terminals for corrosion, damage or terminal push out. Make sure the ground circuit is functional. Repair as necessary. Replace the Fuel Pump Module. Fuel Tank - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
13. (F344) ASD RELAY OUTPUT CIRCUIT
1. Turn the ignition off.
2. Disconnect the Coil on Plug harness connector.
3. Ignition on, engine not running.
4. With a scan tool, actuate the ASD Relay.
5. Using a 12-Volt test light connected to ground, probe the (F344) ASD Relay Output circuit in the Coil on Plug harness connector.
Does the test light illuminate brightly?
Yes
- Go To 14
No
- Repair the open or short to ground in the (F344) ASD Relay Output circuit between the IPM and Coil harness connector.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
- NOTE: Stop All Actuations.
14. IGNITION COIL
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
1. Using a 12-Volt test light connected to a 12 Volt source, probe the (K15) Coil Control No.4 circuit.
2. Crank the engine for 5.0 seconds while observing the test light.
What is the condition of the test light while cranking the engine?
Brightly blinking.
- Replace the Ignition Coil.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
ON constantly.
- Go To 15
OFF constantly.
- Go To 16
15. (K15) COIL CONTROL NO.4 CIRCUIT SHORTED TO GROUND
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance between ground and the (K15) Coil Control No.4 circuit in the Coil on Plug harness connector.
Is the resistance below 100 Ohms?
Yes
- Repair the short to ground in the (K15) Coil Control No.4 circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 17
16. (K15) COIL CONTROL NO.4 CIRCUIT OPEN
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance of the (K15) Coil Control No.4 circuit from the Coil on Plug harness connector to the PCM C2 harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 17
No
- Repair the open in the (K15) Coil Control No.4 circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
17. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Ignition Coil and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Ignition Coil and the Powertrain Control Module connectors.
4. Search for any Technical Service Bulletins that may apply.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Replace and program the Powertrain Control Module.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.