how to fix P0300 code in BMW 3 Series G20/G21 (2019-2024) engine misfire?

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool down completely.

2. Replace Spark Plugs

• Tools Required: Spark plug socket, ratchet, torque wrench.
• Sub-steps:
  1. Remove the engine cover if applicable.
  2. Carefully disconnect the ignition coils from the spark plugs.
  3. Use the spark plug socket to remove the old spark plugs.
  4. Inspect the old plugs for wear and compare them to specifications.
  5. Install the new spark plugs hand-tight, then torque to the manufacturer’s specification (typically around 23 Nm).
  6. Reconnect the ignition coils.

3. Replace Ignition Coils

• Tools Required: Socket set, torque wrench.
• Sub-steps:
  1. Remove the connector from each ignition coil.
  2. Unbolt and remove the ignition coils.
  3. Install the new ignition coils, ensuring they seat properly.
  4. Torque the bolts to manufacturer specifications (usually around 10 Nm).
  5. Reconnect the electrical connectors.

4. Clean or Replace Fuel Injectors

• Tools Required: Fuel injector cleaning kit or replacement injectors, O-rings.
• Sub-steps:
  1. Remove the fuel rail and disconnect the fuel lines carefully (use caution as fuel may leak).
  2. Inspect fuel injectors for clogging or damage.
  3. If cleaning, utilize a fuel injector cleaning kit per the manufacturer's instructions.
  4. If replacing, install new O-rings on the new injectors and replace them in the fuel rail.
  5. Reattach the fuel rail and lines, ensuring no leaks.

5. Inspect for Vacuum Leaks

• Tools Required: Smoke machine or carburetor cleaner.
• Sub-steps:
  1. Use a smoke machine to check for vacuum leaks in hoses and the intake manifold.
  2. If using carburetor cleaner, spray around suspected areas and monitor for RPM changes.
  3. Replace any damaged vacuum hoses or gaskets found during inspection.

6. Check Fuel Pressure

• Tools Required: Fuel pressure gauge.
• Sub-steps:
  1. Connect the fuel pressure gauge to the fuel rail test port.
  2. Turn the ignition on (do not start the engine) and check the pressure reading against specifications (typically 50-60 psi).
  3. If pressure is low, diagnose the fuel pump and filter for replacement.