P0304

P0304-CYLINDER # 4 MISFIRE

For complete wiring diagrams refer to Diagrams/Electrical.


- When Monitored:

While the engine is idling at operating temperature.

- Set Condition:

Misfire detected on this cylinder.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test


1. LOW FUEL

Using the scan tool, verify that the fuel level is above 15%.

Is the fuel level above 15%?

Yes

- Go To 2

No

- Add fuel go to step 2.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. OTHER DTC'S

Read the Freeze frame data.

Is the DTC equal to the freeze frame DTC?

Yes

- Go To 3

No

- Repair any other DTC's first.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

3. DAMAGED FUEL LINE

Visually inspect the injector supply line for damage.

Do you have any kinked or bent fuel line?

Yes

- Repair or replace the damaged fuel line.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 4

4. VALVE TRAIN

Visually inspect the valve train and check the valve lash on the suspect cylinder.

Is the valve train functional and the lash within the specifications?

Yes

- Go To 5

No

- Adjust the lash or fix or repair any damaged component(s).
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

5. OBSTRUCTED FUEL INJECTOR SUPPLY

Remove the fuel injector supply line for the suspect cylinder.

Inspect both ends of the fuel injector supply line for damage.

Using shop air pressure, blow out the fuel injector supply lines to verify that they are not obstructed.

Are the fuel lines free of debris or damage?

Yes

- Go To 6

No

- Replace the damaged or obstructed fuel injector supply line.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

6. DAMAGED OR OBSTRUCTED HIGH PRESSURE CONNECTOR

Remove the high pressure connector for the suspect cylinder.

Inspect both ends of the high pressure connector for signs of damage.

Using shop air pressure, blow out the high pressure connectors to verify that it is not obstructed.

Are the high pressure connectors free of debris or damage?

Yes

- Go To 7

No

- Replace the damaged or obstructed high pressure connector.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

7. FUEL INJECTOR

Remove the suspect fuel injector.

Are the fuel injectors damaged?

Yes

- Replace the external damaged fuel injector & high pressure connector.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 8

8. INTERNAL DAMAGED FUEL INJECTOR

With the scan tool, erase DTCs.

Switch the misfiring injectors & high pressure connector with an injector & high pressure connector from a cylinder that is firing properly.

Operate the vehicle.

Did the misfire DTC follow the suspect injectors & high pressure connectors?

Yes

- Replace the internal damaged fuel injector and high pressure connector.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 9

9. INTERNAL ENGINE DAMAGE

Perform engine compression test. Symptom Related Diagnostic Procedures

Did the suspect cylinders pass the compression test?

Yes

- Go To 10

No

- Repair the internal damage to the engine.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

10. INTERNAL ENGINE DAMAGE

Perform engine leak down test. Symptom Related Diagnostic Procedures

Did the suspect cylinders pass the leak down test?

Yes

- Test Complete.

No

- Repair the internal damage to the engine.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test