how to fix P0302 misfire code on my BMW 3 Series E90/E91

Solution

1. Preparation

• Gather tools and materials, including an OBD-II scanner, socket set, torque wrench, spark plug socket, compression tester, and a multimeter.
• Disconnect the vehicle battery to ensure safety while working on electrical components.

2. Replace Spark Plug and Ignition Coil

• Remove Engine Cover: Use a socket set to unscrew and remove the engine cover.
• Remove Ignition Coil:
  • Disconnect the electrical connector from the ignition coil.
  • Unbolt the ignition coil using a socket.
  • Pull the ignition coil out carefully.
• Replace Spark Plug:
  • Use a spark plug socket to remove the spark plug from cylinder 2.
  • Inspect the old spark plug for wear and carbon buildup.
  • Install a new spark plug, ensuring it is gapped to the manufacturer’s specifications (usually around 0.028-0.032 inches).
  • Torque the spark plug to the manufacturer’s specification (typically around 18-25 Nm).
• Install New Ignition Coil:
  • Insert the new ignition coil into cylinder 2 and bolt it in place.
  • Reconnect the electrical connector.

3. Test Fuel Injector

• Inspect Fuel Injector:
  • If the spark plug and ignition coil replacement does not resolve the issue, test the fuel injector.
  • Disconnect the fuel injector wiring and use a multimeter to check for proper resistance (should be within the manufacturer’s specifications).
• Replace Fuel Injector:
  • If faulty, remove the fuel rail to access the injector.
  • Replace with a new injector and ensure proper sealing.

4. Perform Compression Test

• Conduct Compression Test:
  • Reconnect the battery.
  • Remove the spark plug from cylinder 2 and install the compression tester.
  • Crank the engine and record the compression reading. It should be within the manufacturer’s specified range (usually 140-200 psi).
  • If low, investigate potential internal engine issues (e.g., valve problems, head gasket).