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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Replace Spark Plug

• Tools Required: Socket set, torque wrench.
• Sub-steps:
  1. Remove the ignition coil from cylinder 1 by unbolting and lifting it out.
  2. Unscrew the spark plug using a spark plug socket and ratchet.
  3. Inspect the spark plug for signs of wear, such as excessive carbon buildup or damage.
  4. Install a new spark plug, torquing it to the manufacturer’s specified value (usually around 18-22 lb-ft).

3. Check and Replace Ignition Coil

• Tools Required: Socket set.
• Sub-steps:
  1. If the spark plug was fine, test the ignition coil by swapping it with a known good coil from another cylinder (e.g., cylinder 2).
  2. Reconnect the battery and start the engine to see if the misfire moves to the other cylinder.
  3. If it does, replace the faulty ignition coil in cylinder 1.

4. Inspect and Clean Fuel Injector

• Tools Required: Fuel injector cleaning kit or replacement fuel injector.
• Sub-steps:
  1. Remove the fuel injector from cylinder 1 by unbolting the fuel rail and disconnecting the electrical connector.
  2. Inspect the injector for clogs or deposits.
  3. Clean the injector using a fuel injector cleaning kit or replace it if necessary.
  4. Reinstall the injector and ensure proper seating and connections.

5. Conduct Compression Test (if necessary)

• Tools Required: Compression tester.
• Sub-steps:
  1. Remove the spark plug from cylinder 1.
  2. Insert the compression tester into the spark plug hole.
  3. Crank the engine a few times and record the compression reading.
  4. Compare the reading to the manufacturer’s specifications (usually around 180-200 psi).
  5. If compression is low, further investigation into the engine internals may be required.