P0304 Cylinder 4 Misfire

Possible causes code P0304 Cylinder 4 Misfire

• ASD relay output.
• Injector control circuit.
• Coil control circuit.
• Ignition wire.
• Spark plug.
• Ignition coil.
• Fuel delivery system issue.
• Fuel injector.
• Engine mechanical.
• Powertrain Control Module (PCM).

Diagnose code P0304 Cylinder 4 Misfire

(Sorry!!! Step 1-2, refer to code P0301)
Step 1. Check for an active DTC

Step 2. Visual Inspection

(Sorry!!! Step 3-5, refer to code P0302)

Step 3. Ignition system operation

Step 4. Spark plug

Step 5. Fuel pressure check

(Sorry!!! Step 6-8, refer to code P0303)

Step 6. Fuel pressure leak down

Step 7. Fuel injector operation

Step 8. Engine mechanical

Step 9. Fuel injector control

Turn the ignition off, disconnect the fuel injector harness connector of the misfiring cylinder. Turn the ignition on. When a misfire is detected for a particular cylinder, the PCM will shut down the injector control control circuit for that cylinder.

Install an injector noid light. 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 Powertrain Control Module (PCM) connectors. If problems not are found, replace the fuel injector.

No, go to step 10.

Step 10. Injector control circuit

Turn the ignition off, remove the injector noid light. Disconnect the PCM harness connector, 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.

No, go to step 17.

Step 11. Fuel supply line restricted

Turn the ignition off, raise the vehicle on a hoist and disconnect the fuel pressure line at the fuel pump module.

Install the decay tool between the fuel supply line and the fuel pump module. Turn the ignition on, with the scan tool, actuate the ASD fuel system and observe the fuel pressure gauge. Fuel pressure specification is 400 kpa +/- 14 kpa 8 psi +/- 2 psi)

Is the fuel pressure within specification?

Yes, repair or replace fuel supply line as necessary.

No, go to step 12.

(Sorry!!! Step 12-14, refer to code P0305)
Step 12. Fuel pump inlet strainer

Step 13. ASD relay output circuit

Step 14. Ignition coil

(Sorry!!! Step 15-17, refer to code P0306)

Step 15. Coil control 4 circuit shorted to ground

Step 16. Coil control 4 circuit open

Step 17. Powertrain Control Module (PCM)

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