how to diagnose P0302 misfire code in my BMW 3 Series F30/F31 (2012-2019)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.

2. Inspect and Replace Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket
• Remove the engine cover if necessary.
• Locate the spark plug for cylinder 2.
• Use a spark plug socket to remove the spark plug.
• Inspect the spark plug for signs of wear, carbon buildup, or damage. Replace if necessary, ensuring the gaps are set according to manufacturer specifications (typically around 0.030 inches for BMW).
• Install the new spark plug and torque it to the manufacturer's specification (usually around 20 Nm).

3. Check and Replace Ignition Coil

• Tools Required: Socket set, torque wrench
• Disconnect the electrical connector from the ignition coil.
• Remove the ignition coil from cylinder 2.
• Swap the ignition coil with another cylinder (e.g., cylinder 1) and clear the codes.
• Start the engine and check if the misfire code follows the ignition coil to the other cylinder. If the misfire moves, replace the ignition coil.

4. Inspect and Replace Fuel Injector

• Tools Required: Fuel injector puller, O-ring lube
• Disconnect the fuel injector connector.
• Remove the fuel rail to access the injector for cylinder 2.
• Carefully pull out the fuel injector.
• Inspect the injector for clogs or damage. Clean or replace if necessary.
• Apply O-ring lube to the new injector and install it back in place, ensuring a secure fit.

5. Perform Compression Test

• Tools Required: Compression tester
• Remove the spark plug for cylinder 2.
• Insert the compression tester into the spark plug hole.
• Crank the engine and record the compression reading. Compare it to the manufacturer's specifications (typically around 140-200 psi). Low readings may indicate internal engine issues.