why does my BMW 3 Series E90/E91 (2005-2012) have poor fuel economy lately

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery before starting work on electrical components.

2. Replace Air Filter

• Sub-steps:
  1. Open the hood and locate the air filter housing.
  2. Remove the screws or clips securing the housing.
  3. Carefully lift off the housing cover and remove the old air filter.
  4. Install the new air filter, ensuring a snug fit.
  5. Re-secure the housing cover with screws or clips.

3. Replace Spark Plugs

• Tools Required: Spark plug socket, torque wrench.
• Sub-steps:
  1. Remove the ignition coil covers to access the spark plugs.
  2. Disconnect the electrical connectors from the ignition coils.
  3. Unbolt and remove the ignition coils.
  4. Use a spark plug socket to remove old spark plugs.
  5. Install new spark plugs, ensuring they are gapped correctly.
  6. Reinstall the ignition coils and electrical connectors.

4. Inspect and Replace Fuel Filter (if necessary)

• Sub-steps:
  1. Locate the fuel filter, typically found along the fuel line.
  2. Relieve fuel system pressure by removing the fuel pump fuse and running the engine until it stalls.
  3. Disconnect the fuel lines from the old filter using line wrenches.
  4. Install the new fuel filter in the correct orientation.
  5. Reconnect the fuel lines and check for leaks.

5. Check for Vacuum Leaks

• Sub-steps:
  1. Inspect all vacuum hoses for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner to check for leaks around gaskets and hoses.
  3. Replace any damaged hoses or gaskets.