how to fix P0304 code in Ford F-150 12th Generation (2009-2014)

Learn how to diagnose and fix P0304 cylinder 4 misfire in Ford F-150 (2009-2014). Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, compression tester, noid light, torque wrench, fuel pressure gauge.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Replace Spark Plug and Coil

• Sub-steps:
  1. Remove the engine cover (if applicable) using a socket set.
  2. Disconnect the ignition coil connector for cylinder 4.
  3. Remove the ignition coil by unscrewing the bolts and pulling it out.
  4. Remove the spark plug using a spark plug socket.
  5. Install the new spark plug by hand to avoid cross-threading, then tighten to manufacturer specifications (typically around 13 lb-ft).
  6. Reinstall the ignition coil and reconnect the connector.

3. Test Fuel Injector

• Sub-steps:
  1. Disconnect the fuel injector connector for cylinder 4.
  2. Connect a noid light to the connector to check for proper signal when the engine is cranked.
  3. If no signal is present, follow wiring back to the ECU and check for faults.
  4. If the signal is present, use a fuel pressure gauge to check for adequate fuel pressure at the rail.

4. Compression Test

• Sub-steps:
  1. Remove the spark plug from cylinder 4 and insert the compression tester.
  2. Crank the engine for a few seconds and note the compression reading.
  3. Compare the reading to the manufacturer specifications (usually around 120-160 psi).
  4. If compression is low, further investigation is needed into the piston rings or valves.