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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal for safety.

2. Inspect and Replace Spark Plug

• Tools Required: Spark plug socket, ratchet, torque wrench, dielectric grease.
• Remove the engine cover if applicable.
• Disconnect the ignition coil connector on cylinder 1.
• Remove the ignition coil by pulling it straight out.
• Use the spark plug socket to remove the spark plug.
• Inspect the spark plug for damage and ensure the gap is correct (typically 0.028-0.032 inches).
• Install the new spark plug hand-tight, then torque to manufacturer specifications (usually around 18 lb-ft).
• Apply dielectric grease to the ignition coil connector.
• Reinstall the ignition coil and reconnect the connector.

3. Inspect and Replace Ignition Coil

• Tools Required: Same as above.
• If the ignition coil is faulty, remove it as previously mentioned.
• Install a new ignition coil, ensuring it is seated properly.
• Reconnect the ignition coil connector.

4. Inspect Fuel Injector

• Tools Required: Fuel injector tool (if necessary).
• Check if the injector is clogged or not functioning.
• If replacement is needed, disconnect the fuel line carefully (ensure to relieve fuel system pressure).
• Remove the old injector and install the new one, ensuring proper seating and connection.

5. Verify Compression

• Tools Required: Compression tester.
• Remove the spark plug from cylinder 1.
• Insert the compression tester and crank the engine to take the reading.
• Compare with manufacturer specifications (typically around 140-200 psi).
• If low, further diagnosis may be required for mechanical issues.