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

Solution

1. Preparation

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

2. Inspect and Replace Spark Plug

• Tools Required: Socket set, torque wrench.
• Remove the engine cover if applicable.
• Use a spark plug socket to remove the spark plug from cylinder 1.
• Inspect the spark plug for wear or fouling.
• If damaged, install a new spark plug, ensuring it is gapped according to manufacturer specifications (typically 0.030 to 0.035 inches).
• Torque the new spark plug to the specified value (usually around 18-22 ft-lbs).

3. Check and Replace Ignition Coil

• Tools Required: Socket set, multimeter (for testing).
• Disconnect the electrical connector from the ignition coil on cylinder 1.
• Remove the ignition coil by unbolting it or pulling it out (depending on the design).
• Test the ignition coil with a multimeter to ensure it is functioning properly (check resistance).
• If faulty, replace it with a new ignition coil and reconnect the electrical connector.

4. Inspect and Clean Fuel Injector

• Tools Required: Fuel injector cleaning kit (if needed).
• Remove the fuel rail if necessary to access the injector for cylinder 1.
• Inspect the fuel injector for clogs or damage.
• If clogged, clean the injector using a fuel injector cleaning kit or replace it if necessary.
• Reinstall the fuel rail and ensure all connections are secure.

5. Verify Compression

• Tools Required: Compression tester.
• Remove the spark plug from cylinder 1.
• Insert the compression tester into the spark plug hole.
• Crank the engine a few times and record the compression reading.
• Compare the reading to the manufacturer's specifications (usually around 140-200 psi).
• If compression is low, further engine diagnostics may be needed.