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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Allow the engine to cool before starting work.

2. Replace Spark Plug

• Remove the engine cover (if applicable).
• Use a spark plug socket and ratchet to remove the spark plug from cylinder 1.
• Inspect the old spark plug for wear; if necessary, replace it with a new one.
• Torque the new spark plug to the manufacturer’s specification (usually around 18-22 ft-lbs).
• Reinstall the engine cover.

3. Replace Ignition Coil

• Locate the ignition coil for cylinder 1 (typically on top of the engine).
• Remove the electrical connector from the ignition coil.
• Unscrew and remove the ignition coil.
• Install the new ignition coil and torque to manufacturer specifications.
• Reconnect the electrical connector.

4. Inspect and Clean Fuel Injector

• Remove the fuel rail (if necessary) to access the fuel injector for cylinder 1.
• Disconnect the electrical connector and fuel line from the injector.
• Remove the fuel injector.
• Clean the injector using a dedicated fuel injector cleaner or replace it if it is clogged.
• Reinstall the fuel injector and reconnect all lines and connectors.

5. Perform Compression Test

• If misfire persists, perform a compression test on cylinder 1.
• Remove the spark plug and insert the compression gauge into the spark plug hole.
• Crank the engine and record the compression reading.
• Compare the reading with manufacturer specifications. If low, further investigation into the valve or piston may be needed.