how to diagnose a misfire in my BMW 3 Series E90/E91 (2005-2012) with code P0302

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool if it has been running.

2. Inspect and Replace Spark Plug

• Sub-steps:
  1. Remove the engine cover if applicable.
  2. Locate and remove the spark plug for cylinder 2 using a socket wrench and extension.
  3. Inspect the spark plug for wear, fouling, or damage. Replace if necessary.
  4. Check the gap on the new spark plug and adjust to manufacturer specifications.
  5. Install the new spark plug and torque to the specified value (typically 18-22 lb-ft).

3. Check and Replace Ignition Coil

• Sub-steps:
  1. Disconnect the electrical connector from the ignition coil for cylinder 2.
  2. Remove the ignition coil using a socket or wrench.
  3. Inspect the ignition coil for cracks or wear. Replace if needed.
  4. Install the new ignition coil and reconnect the electrical connector.

4. Inspect and Clean Fuel Injector

• Sub-steps:
  1. Disconnect the fuel injector connector for cylinder 2.
  2. Remove the fuel rail bolts and carefully lift the rail to access the injector.
  3. Inspect the injector for clogs; clean with an appropriate injector cleaner if needed.
  4. Reinstall the fuel injector and ensure it is seated properly in the rail.

5. Final Assembly

• Sub-steps:
  1. Reinstall the fuel rail and secure it with bolts to the manufacturer's torque specs.
  2. Reconnect all electrical connectors and vacuum lines that were disconnected.
  3. Reconnect the negative battery terminal.