how to fix P0301 misfire code on my BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather all necessary tools and parts before starting.
• Disconnect the negative terminal of the battery to prevent electrical shorts.
• Allow the engine to cool before beginning work on ignition components.

2. Replace Spark Plug

• Sub-steps:
  1. Remove the engine cover, if applicable, using a socket set.
  2. Disconnect the ignition coil connector from the ignition coil in cylinder 1.
  3. Remove the ignition coil by pulling it straight up.
  4. Unscrew the spark plug using a spark plug socket and ratchet.
  5. Inspect the spark plug for wear; replace if necessary with OEM specifications.
  6. Gap the new spark plug according to manufacturer specifications (usually around 0.028-0.032 inches).
  7. Install the new spark plug and torque it to the manufacturer’s specifications (typically 15-20 Nm).
  8. Reinstall the ignition coil and reconnect the connector.

3. Replace Ignition Coil (if necessary)

• Sub-steps:
  1. If the ignition coil tests faulty, remove it as described above.
  2. Install the new ignition coil (ensure it matches OEM specifications).
  3. Reconnect the ignition coil connector securely.
  4. Repeat for any additional cylinders if misfires are detected on others.

4. Inspect and Clean Fuel Injector

• Sub-steps:
  1. Remove the fuel rail (may require disconnecting fuel lines and electrical connectors).
  2. Carefully remove the injector from cylinder 1 from the rail.
  3. Inspect the injector for clogs or damage; replace if necessary.
  4. Clean the injector with a specialized cleaner or replace it.
  5. Reinstall the injector and secure the fuel rail.

5. Check for Vacuum Leaks

• Sub-steps:
  1. Visually inspect all hoses around the intake manifold for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner to check for leaks while the engine is running.
  3. Repair or replace any damaged hoses as necessary.