my Ford F-150 has a check engine light with code P0304, what's wrong?

Learn how to diagnose and fix P0304 cylinder 4 misfire in Ford F-150. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool if it has been running.

2. Inspect and Replace Ignition Components

• Spark Plug Inspection and Replacement

  • Remove the ignition coil from cylinder 4 using a socket set.
  • Inspect the spark plug for wear; replace if necessary with OEM specifications (typically gap at 0.054 inches).
  • Reinstall the ignition coil securely.

• Ignition Coil Replacement (if necessary)

  • If the ignition coil shows signs of failure (cracks, carbon tracking), replace it with a new OEM coil.
  • Torque the ignition coil bolts to manufacturer specifications (typically around 7-10 ft-lbs).

3. Fuel Injector Inspection and Testing

• Remove the fuel injector from cylinder 4 using a socket set.
• Test the injector with a noid light to ensure it is receiving the proper signal; replace if it does not activate.
• Clean or replace the fuel injector as needed, ensuring to use proper O-rings during reinstallation.

4. Perform Compression Test

• If misfire persists, perform a compression test on cylinder 4.
• If compression is low (below manufacturer specifications), further investigation into valve or piston issues may be required.
• Reassemble any components removed for access.

5. Inspect for Vacuum Leaks

• Visually inspect all vacuum lines connected to the intake manifold and cylinder 4.
• Use a smoke machine or carburetor cleaner to identify leaks.
• Replace any damaged hoses or seals.