how to fix the P0301 misfire code on my 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 to prevent electrical shorts.

2. Replace Spark Plug

• Tools Required: Socket set, torque wrench, gap gauge
• Remove the ignition coil by unscrewing the retaining bolts and gently pulling it out.
• Remove the spark plug using a spark plug socket and ratchet.
• Inspect the old spark plug; replace it if worn or fouled.
• Install the new spark plug, ensuring proper gap (typically 0.032-0.036 inches).
• Torque the spark plug to the manufacturer's specification (usually around 15 lb-ft).

3. Replace Ignition Coil (if needed)

• Tools Required: Socket set
• If the ignition coil is faulty, replace it with a new one.
• Ensure the new ignition coil is seated properly and secure it with the bolts.

4. Inspect Fuel Injector

• Tools Required: Fuel injector cleaner, multimeter (optional)
• If the injector is clogged, use a fuel injector cleaner to clean it or replace it if necessary.
• Test the fuel injector resistance with a multimeter to ensure it falls within the specified range (usually around 12-16 ohms).

5. Reassemble and Reconnect

• Reinstall the ignition coil and secure it.
• Reconnect the negative battery terminal.
• Start the engine and allow it to idle for a few minutes to ensure proper operation.