what does it mean if my BMW 3 Series E90/E91 (2005-2012) has a P0300 misfire code?

Solution

1. Preparation

• Gather tools and parts needed.
• Disconnect the negative battery terminal to ensure safety while working on the vehicle.

2. Inspect and Replace Spark Plugs

• Remove the engine cover if applicable.
• Use a spark plug socket to remove the spark plugs.
• Inspect each spark plug for wear and replace with OEM or equivalent parts if necessary.
  • Torque new plugs to manufacturer specifications (usually around 15-20 ft-lbs).
• Reinstall the engine cover.

3. Inspect and Replace Ignition Coils

• Disconnect the electrical connectors from the ignition coils.
• Remove the ignition coils using a socket wrench.
• Inspect for cracks or damage; replace faulty coils with new ones.
• Reinstall the ignition coils and connect the electrical connectors.

4. Check and Clean Fuel Injectors

• Remove the fuel rail assembly if necessary to access the injectors.
• Inspect fuel injectors for clogs or leaks.
• Clean the injectors using a fuel injector cleaning kit or replace them if they are defective.
• Reassemble the fuel rail and ensure all connections are secure.

5. Test Engine Compression

• Remove spark plugs again for access.
• Use a compression tester to check the pressure in each cylinder.
• Record the values and compare them to manufacturer specifications. Replace or repair any cylinders that are below standard.