P0304
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 1% misfire rate is measured during two trips. Three good trips to clear the MIL.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding Pre-Diagnostic Troubleshooting Procedure.
1. DTC IS ACTIVE
1. Start the engine and allow it to reach operating temperature.
2. With the scan tool, monitor the View DTC screen.
Is the status Active for this DTC?
Yes
- Go To 2
No
- Perform the Checking For An Intermittent DTC procedure. Checking for an Intermittent DTC
2. VISUAL INSPECTION
NOTE: Anything that affects the speed of the crankshaft can cause a misfire DTC to set.
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 or A/C compressor pulleys
- Corroded PCM power or ground circuits.
- Improper CKP, CMP, MAP, or TP Sensor mounting.
- Poor connector/terminal to component connection for CKP, CMP, MAP, or TP sensor, fuel injector, ignition coil, etc.
- Restriction in the air induction or exhaust system.
- Vacuum leaks.
- Internal engine component malfunction.
Were any of the above conditions present?
Yes
- Repair as necessary.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 3
3. (F344) FUSED MAIN RELAY OUTPUT CIRCUIT
1. Turn the ignition off.
2. Disconnect the Fuel Injector 4 connector.
3. Turn the ignition on.
4. Using a 12 volt test light connected to ground, check the (F344) Fused Main Relay Output circuit in the Fuel Injector 4 harness connector.
NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.
Is the test light illuminated and bright?
Yes
- Go To 4
No
- Repair the (F344) Fused Main Relay Output circuit for high resistance or a short to ground.
- Perform the PCM Verification Test PCM Verification Test.
4. (F342) FUSED MAIN RELAY OUTPUT CIRCUIT
1. Turn the ignition off.
2. Disconnect the Ignition Coil 4 connector.
3. Turn the ignition on.
4. Using a 12 volt test light connected to ground, check the (F342) Fused Main Relay Output circuit in the Ignition Coil 4 harness connector.
NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.
Is the test light illuminated and bright?
Yes
- Go To 5
No
- Repair the (F342) Fused Main Relay Output circuit for high resistance or a short to ground.
- Perform the PCM Verification Test PCM Verification Test.
5. IGNITION SYSTEM OPERATION
1. Turn the ignition off.
2. Remove the Ignition Coil 4.
3. Connect the Ignition Coil 4 harness connector.
NOTE: Leave the Fuel Injector 4 harness connector disconnected.
4. Install a spark tester on the Ignition Coil 4.
5. 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 6
No
- NOTE: Connect the Fuel Injector 4 harness connector before continuing.
Go To 15
6. SPARK PLUG
1. Turn the ignition off.
2. Remove the spark plug.
3. Inspect the spark plug for the following conditions:
- Cracks
- Carbon tracking
- Foreign material
- Spark plug gap out of specifications
- Loose or broken electrode
NOTE: To check the electrode, lightly tap the bottom of the spark plug on a solid surface. The electrode should not move.
Were any problems found?
Yes
- Replace the spark plug.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 7
7. FUEL PRESSURE OUT OF SPECIFICATION
NOTE: Before continuing, install any components that were removed for testing, and connect all harness connectors.
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.
1. Turn the ignition off.
2. Install a fuel pressure gauge to the fuel rail.
3. Start the engine and observe the fuel pressure reading.
NOTE: The fuel pressure specification is 407 KPa ± 34 KPa (59 psi ± 5 psi).
Select the conclusion that best matches the fuel pressure reading:
Within Specification
- Go To 8
Below Specification
- Go To 13
Above Specification
- Replace the fuel pump module.
- Perform the PCM Verification Test PCM Verification Test.
8. FUEL INJECTOR LEAK DOWN
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 personal injury or death
1. Perform the diagnostic procedure for FUEL PRESSURE LEAK DOWN. Fuel Pressure Leak Down.
Does the pressure drop below the listed specification?
Yes
- Perform the repair specified in the procedure.
No
- Go To 9
9. FUEL INJECTOR OPERATION
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.
CAUTION: After each fuel injector actuation, start the engine to clear the cylinder of fuel. Failure to do so could cause engine damage.
1. Remove special tool #C4390.
2. Start the engine and allow the fuel pressure to reach maximum pressure.
3. Ignition on, engine not running.
4. Using the scan tool, actuate the Fuel Injector 4 control.
5. Monitor the fuel pressure gauge.
Does the fuel pressure drop after the injector is actuated?
Yes
- Go To 10
No
- NOTE: Turn the ignition off, remove the Fuel Pressure gauge, and connect the fuel lines before continuing.
Go To 11
10. INTERNAL ENGINE COMPONENT
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
- CAM LOBES - must not be worn excessively
- CYLINDER LEAKAGE TEST - must be within specifications
- VALVE SPRINGS - must not be weak or broken
Were any problems found?
Yes
- Repair as necessary.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 17
11. FUEL INJECTOR 4
1. Turn the ignition off.
2. Disconnect the Fuel Injector 4 harness connector.
3. Turn the ignition on.
4. With the scan tool, clear DTCs.
5. With the scan tool, actuate the Fuel Injector 4 control.
6. Using a 12 volt test light connected to 12 volts check the (K14) Injector 4 Control circuit in the Fuel Injector 4 harness connector.
NOTE: The test light should blink each time the circuit is activated by the PCM.
Does the test light blink each time the circuit is activated by the PCM?
Yes
- Replace the Fuel Injector 4.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 12
12. (K14) INJECTOR 4 CONTROL CIRCUIT
1. Turn the ignition off.
2. Disconnect the Powertrain Control Module (PCM) harness connector.
3. Check the (K14) Injector 4 Control circuit for an open circuit, short to ground, and short to voltage.
Were any problems found?
Yes
- Repair the (K14) Injector 4 Control circuit for high resistance or a shorted condition.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 17
13. FUEL SUPPLY LINE RESTRICTED
1. Turn the ignition off.
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.
2. Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.
3. Install special tool #6539 (for 5/16) or #6631 (for 3/8) fuel line adapter and the fuel pressure gauge between the fuel supply line and the fuel pump module.
4. Turn the ignition on.
5. With the scan tool, actuate the fuel pump to ON (100%) and observe the fuel pressure gauge.
NOTE: Fuel pressure specification is 407 KPa ± 34 KPa (59 psi ± 5 psi).
NOTE: If the PCM detects a low fuel level, the fuel pump actuation will not be allowed.
Is the fuel pressure within specification?
Yes
- Repair or replace fuel supply line as necessary.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 14
14. FUEL PUMP INLET STRAINER
1. Turn the ignition off.
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.
2. Remove the fuel pump module and inspect the fuel inlet strainer.
Is the fuel inlet strainer plugged?
Yes
- Replace the fuel pump inlet strainer.
- Perform the PCM Verification Test PCM 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. If any problems are found, repair as necessary. Otherwise, replace the fuel pump module.
- Perform the PCM Verification Test PCM Verification Test.
15. IGNITION COIL 4
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. Disconnect the Ignition Coil 4 harness connector.
3. Remove the Fuel Pump Relay.
4. Using a 12 volt test light connected to 12 volts, check the (K15) Coil 4 Control circuit in the Ignition Coil 4 harness connector.
5. Crank the engine for 5 seconds.
NOTE: The test light should blink each time the circuit is activated by the PCM.
Does the test light blink each time the circuit is activated by the PCM?
Yes
- Replace the Ignition Coil 4.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 16
16. (K15) COIL 4 CONTROL CIRCUIT
1. Turn the ignition off.
2. Disconnect the Powertrain Control Module (PCM) harness connector.
3. Check the (K15) Coil 4 Control circuit for an open circuit, short to ground, and short to voltage.
Were any problems found?
Yes
- Repair the (K15) Coil 4 Control circuit.
- Perform the PCM Verification Test PCM Verification Test.
No
- Go To 17
17. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Fuel Injector 4, the Ignition Coil 4, 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.
4. Search for any Technical Service Bulletins that may apply.
Were any problems found?
Yes
- Repair as necessary.
- Perform the PCM Verification Test PCM Verification Test.
No
- Replace and program the Powertrain Control Module (PCM).
- Perform the PCM Verification Test PCM Verification Test.