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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety while working on electrical components.

2. Inspect and Replace Spark Plug

• Remove the ignition coil from cylinder 1 using a socket wrench.
• Extract the spark plug using a spark plug socket.
• Inspect the spark plug for wear. Replace if necessary (recommended gap is typically 0.030 inches for BMW).
• Install a new spark plug, ensuring it is properly gapped.

3. Test and Replace Ignition Coil

• Inspect the ignition coil for signs of damage or wear.
• If faulty, remove the ignition coil by unscrewing it from the cylinder head.
• Install a new ignition coil, ensuring it is seated properly and secure.

4. Check and Replace Fuel Injector

• Disconnect the fuel injector connector for cylinder 1.
• Remove the fuel injector using a fuel injector puller.
• Inspect for clogs or leaks. If faulty, replace with a new injector.
• Reconnect the fuel injector connector after installation.

5. Compression Test (if necessary)

• Remove the spark plug and ignition coil from cylinder 1.
• Insert a compression gauge into the spark plug hole.
• Crank the engine and record the compression reading; compare to manufacturer's specifications.
• If compression is low, further engine diagnostics may be needed (e.g., valve train issues).

6. Reassemble and Reconnect Battery

• Reinstall any components removed during the inspection and repair.
• Reconnect the negative battery terminal.