how to fix P0300 misfire code on BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, fuel pressure gauge, multimeter, compression tester.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shocks.

2. Replace Spark Plugs

1. Remove the engine cover if applicable.
2. Use a socket wrench to carefully remove each spark plug.
3. Inspect the old spark plugs for signs of fouling or damage.
4. Install new spark plugs, ensuring they are gapped correctly according to manufacturer specifications (typically around 0.025-0.035 inches for most BMWs).
5. Torque the spark plugs to the manufacturer’s specified torque (usually around 18-22 ft-lbs).
6. Reinstall the engine cover.

3. Inspect and Replace Ignition Coils

1. Disconnect the electrical connector from each ignition coil.
2. Remove the retaining bolts or clips securing the ignition coils.
3. Pull the ignition coils out of the spark plug wells.
4. Check the ignition coils with a multimeter for proper resistance (consult the repair manual for specified values).
5. Replace any faulty ignition coils with new ones.
6. Reinstall the ignition coils and reconnect the electrical connectors.

4. Check Fuel Pressure

1. Locate the fuel pressure test port on the fuel rail.
2. Connect the fuel pressure gauge to the test port.
3. Turn the ignition key to the "On" position (do not start the engine) and check the fuel pressure reading against manufacturer specifications (typically 50-60 psi).
4. If the pressure is low, inspect the fuel pump and filter for issues and replace if necessary.

5. Inspect for Vacuum Leaks

1. Visually inspect all vacuum lines and intake hoses for cracks or disconnections.
2. Use a smoke machine or carburetor cleaner to identify any vacuum leaks while the engine is running.
3. Repair or replace any damaged hoses or intake components as needed.

6. Perform Compression Test

1. Remove spark plugs for access to the cylinders.
2. Insert the compression tester into the spark plug hole of each cylinder.
3. Crank the engine for several seconds and record the compression readings.
4. Compare the readings to manufacturer specifications (usually around 180-200 psi).
5. Address any cylinders with low compression by checking for valve or piston issues.