how to resolve P0302 misfire code on BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather necessary tools and safety equipment. Ensure the vehicle is parked on a level surface with the engine off and cool.
• Tools Required:
  • OBD-II scanner
  • Socket set
  • Torque wrench
  • Compression tester
  • Noid light or multimeter
  • Screwdrivers
  • Safety gloves and glasses
• Safety Warnings: Disconnect the battery before working on electrical systems.

2. Replace Spark Plug and Ignition Coil

1. Remove Engine Cover: Unscrew and remove any engine covers to access the ignition components.
2. Disconnect Ignition Coil: Unplug the electrical connector from the ignition coil on cylinder 2.
3. Remove Ignition Coil: Unscrew the coil from its mounting and gently pull it out.
4. Remove Spark Plug: Use a spark plug socket to unscrew and remove the spark plug from cylinder 2.
5. Install New Spark Plug: Insert the new spark plug into the cylinder and tighten it to the manufacturer's specifications (typically around 22 lb-ft).
6. Install New Ignition Coil: Place the new ignition coil in the cylinder and secure it with screws. Reconnect the electrical connector.

3. Check and Replace Fuel Injector (if necessary)

1. Remove Fuel Rail: Detach the fuel rail to access the injectors. Relieve fuel pressure before removal by removing the fuel pump fuse and running the engine until it stalls.
2. Remove Injector: Unscrew and carefully pull out the injector from cylinder 2.
3. Install New Fuel Injector: Insert the new injector in place, ensuring it is seated properly, and secure it.
4. Reinstall Fuel Rail: Attach the fuel rail back to its original position and ensure all connections are tight.

4. Perform Compression Test

1. Connect Compression Tester: Remove the spark plug for cylinder 2 and screw in the compression tester.
2. Crank Engine: Have an assistant crank the engine for about 5 seconds while you observe the compression gauge.
3. Record Compression Reading: Compare the reading with the manufacturer’s specifications (usually between 140-200 psi). If it's low, further investigation into the cylinder's mechanical condition is needed.