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

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the battery to ensure safety.
• Allow the engine to cool before starting work.

2. Replace Spark Plug

• Sub-steps:
  1. Remove the engine cover if applicable.
  2. Locate the spark plug for cylinder 1.
  3. Disconnect the ignition coil connector.
  4. Remove the ignition coil by unscrewing it and carefully pulling it out.
  5. Use a spark plug socket to remove the old spark plug.
  6. Check the gap on the new spark plug and adjust as necessary.
  7. Install the new spark plug, tightening to the manufacturer’s specified torque (typically around 18 lb-ft).
  8. Reinstall the ignition coil and reconnect the connector.

3. Replace Ignition Coil (if necessary)

• Sub-steps:
  1. If the ignition coil shows signs of failure, obtain a new ignition coil.
  2. Remove the faulty ignition coil as described above.
  3. Install the new ignition coil, ensuring it is seated properly.
  4. Reconnect the ignition coil connector.

4. Inspect Fuel Injector (if necessary)

• Sub-steps:
  1. If the injector appears clogged, remove it from cylinder 1 following the manufacturer's procedure.
  2. Clean the injector using an injector cleaning kit or replace it with a new one if it’s damaged.
  3. Reinstall the injector ensuring a proper seal.

5. Conduct a Compression Test (if necessary)

• Sub-steps:
  1. Remove the spark plug from cylinder 1.
  2. Insert a compression gauge into the spark plug hole.
  3. Crank the engine and check the compression reading; compare with manufacturer specifications (usually around 140-200 psi).
  4. If compression is low, further diagnosis may be needed (e.g., checking valve seals or piston rings).