how to address 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 while working on electrical components.

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 spark plug for any signs of wear or fouling.
• Install a new spark plug, ensuring it is gapped correctly (typically 0.032-0.036 inches for BMW).
• Torque the spark plug to the manufacturer's specification (usually around 18 ft-lbs).

3. Inspect and Replace Ignition Coil

• Disconnect the electrical connector from the ignition coil on cylinder 1.
• Remove the ignition coil using a socket set.
• Inspect the coil for cracks or damage; if faulty, replace with a new ignition coil.
• Reinstall the new ignition coil and reconnect the electrical connector.

4. Check and Clean Fuel Injector

• Disconnect the fuel injector connector for cylinder 1.
• Use a fuel injector cleaning tool or spray cleaner to clean the injector.
• If the injector is still malfunctioning, remove it using a fuel injector puller and replace it.

5. Verify Fuel Pressure

• Connect a fuel pressure gauge to the fuel rail.
• Turn the ignition to the "on" position (do not start the engine) and check the pressure reading against specifications (typically around 50-60 psi).
• If the pressure is low, inspect the fuel pump and fuel filter for blockage or failure.

6. Perform Compression Test

• Remove the spark plug from cylinder 1.
• Insert a compression gauge into the spark plug hole and crank the engine.
• Compare the reading with specifications (usually around 150 psi). If low, further mechanical inspection may be needed.