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

Solution

1. Preparation

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

2. Inspect and Replace Spark Plug

1. Remove the engine cover (if applicable) using a socket set.
2. Locate the spark plug for cylinder 1 (usually at the front of the engine).
3. Use a spark plug socket to remove the spark plug.
4. Inspect the spark plug for wear; replace it if it shows signs of fouling or damage.
5. Apply a small amount of anti-seize compound to the threads of the new spark plug and install it to the manufacturer's torque specification (usually around 15 lb-ft).
6. Reconnect the ignition coil.

3. Check and Replace Ignition Coil

1. Remove the ignition coil from cylinder 1 by disconnecting the electrical connector and unscrewing any retaining bolts.
2. Using a multimeter, test the ignition coil for the specified resistance (refer to the service manual for values).
3. If the coil is faulty, install a new ignition coil.
4. Reconnect the ignition coil and ensure it is seated properly.

4. Inspect Fuel Injector

1. Remove the fuel rail if necessary to access the fuel injector for cylinder 1.
2. Check for any clogs or leaks in the injector.
3. If the injector is faulty, replace it with a new one and ensure proper reinstallation.

5. Compression Test

1. Remove the spark plug from cylinder 1.
2. Use a compression tester to check the compression in cylinder 1.
3. If the compression is low, further diagnosis may be required for potential internal engine issues (e.g., valve problems, piston rings).