how to fix P0304 misfire code on my Toyota Corolla E140 (2006-2013)

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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool completely before beginning work.

2. Replace Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket
• Remove the ignition coil from cylinder 4 by unscrewing the mounting bolts.
• Pull the coil straight out from the spark plug.
• Using a spark plug socket, remove the old spark plug from cylinder 4.
• Inspect the new spark plug for proper gap size (0.043 inches for a typical Corolla).
• Install the new spark plug and torque it to the manufacturer's specification (approximately 13 lb-ft).
• Reinstall the ignition coil, securing it with the bolts.

3. Test and Replace Ignition Coil (if necessary)

• Tools Required: Multimeter
• Measure the resistance of the ignition coil; compare it to specifications (typically 0.5 to 0.7 ohms for primary and 10,000 to 15,000 ohms for secondary).
• If the readings are out of specification, replace the ignition coil with a new one.
• Reconnect the coil and ensure all connections are secure.

4. Inspect and Clean Fuel Injector

• Tools Required: Noid light or equivalent fuel injector tester
• Connect the noid light to the fuel injector connector for cylinder 4.
• Crank the engine to check for light activation, indicating injector pulse.
• If no signal is detected, check wiring and replace the injector if necessary.
• If the injector is functional, remove it and clean it using a dedicated fuel injector cleaner. Reinstall after cleaning.

5. Perform Compression Test

• Tools Required: Compression tester
• Remove the spark plug and ignition coil.
• Insert the compression tester into the spark plug hole of cylinder 4.
• Crank the engine and record the compression reading; it should be within the manufacturer's specified range (typically around 180 psi).
• If compression is low, further investigation of internal engine components may be necessary.