how to diagnose a misfire in my BMW 5 Series G30/G31 (2017-2024) with code P0301

Solution

1. Preparation

• Tools Required: OBD-II scanner, spark plug socket, torque wrench, multimeter, compression tester, fuel injector cleaner.
• Ensure the vehicle is parked on a level surface and engine is cool. Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Spark Plug

• Remove the engine cover if necessary.
• Use a spark plug socket to remove the spark plug from cylinder 1.
• Inspect the spark plug for damage or excessive wear.
• If damaged, replace with a new spark plug that meets OEM specifications (e.g., NGK or Bosch).
• Torque the new spark plug to manufacturer’s specifications (typically around 23 Nm).

3. Test and Replace Ignition Coil

• Disconnect the ignition coil connector from cylinder 1.
• Use a multimeter to measure the resistance of the ignition coil; compare it to the service manual specifications.
• If the ignition coil is faulty, replace it with a new one (ensure it matches the OEM part number).
• Reconnect the ignition coil connector and ensure it's secured properly.

4. Perform Compression Test

• Remove the spark plug from cylinder 1.
• Insert the compression tester into the spark plug hole.
• Crank the engine for a few seconds and record the compression reading.
• If the reading is lower than the manufacturer’s specification, further investigation is needed (possible head gasket issue, valve timing, etc.).

5. Inspect and Clean Fuel Injector

• Disconnect the electrical connector from the fuel injector for cylinder 1.
• Remove the fuel rail (if necessary) to access the injector.
• Inspect the fuel injector for clogs or leaks.
• Clean the injector using a fuel injector cleaner or replace if necessary.
• Reinstall the fuel injector and ensure proper sealing.