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

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, multimeter, compression tester, torque wrench
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool before beginning work.

2. Inspect and Replace Ignition Components

• Sub-steps:
  1. Remove the engine cover if applicable.
  2. Disconnect the ignition coil connector for cylinder 2.
  3. Remove the ignition coil from cylinder 2 using the socket set.
  4. Inspect the spark plug for wear or damage; replace if necessary.
  5. Install a new spark plug (gap to manufacturer's specifications).
  6. Reinstall the ignition coil and reconnect the connector.

3. Examine Fuel Injector

• Sub-steps:
  1. Remove the fuel rail if necessary to access the fuel injector for cylinder 2.
  2. Disconnect the fuel injector connector.
  3. Inspect the injector for clogs or electrical failure.
  4. If faulty, replace the fuel injector with a new one.
  5. Reinstall the fuel rail and reconnect all connections.

4. Compression Test

• Sub-steps:
  1. Remove the spark plug from cylinder 2.
  2. Insert the compression tester into the spark plug hole.
  3. Crank the engine for a few seconds and record the compression reading.
  4. Compare the reading with the manufacturer's specifications.
  5. If low, further diagnose potential issues such as valve or head gasket problems.

5. Final Assembly

• Sub-steps:
  1. Reinstall all components removed during the inspection.
  2. Reconnect the negative battery terminal.
  3. Start the engine and allow it to reach operating temperature.