what can cause engine misfires in BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative terminal of the battery for safety.

Tools Required:

• OBD-II scanner
• Socket set
• Multimeter
• Fuel pressure gauge
• Compression tester

2. Replace Spark Plugs

• Remove the ignition coils by unbolting them and disconnecting the electrical connectors.
• Use a spark plug socket to remove the old spark plugs.
• Inspect the spark plugs and replace with OEM or equivalent parts, ensuring they are gapped correctly.

3. Replace Ignition Coils

• After removing the spark plugs, install new ignition coils.
• Ensure each coil is seated properly and reconnect the electrical connectors.

4. Inspect and Replace Fuel Injectors

• Remove the fuel rail by unbolting it from the intake manifold.
• Disconnect injector electrical connectors and remove the injectors from the rail.
• Inspect and clean the injectors; replace any that are faulty.

5. Check Fuel Pressure

• Connect the fuel pressure gauge to the fuel rail test port.
• Turn the ignition to the "ON" position (do not start the engine) and check the fuel pressure reading against manufacturer specifications.
• If pressure is low, inspect the fuel pump and fuel filter; replace as needed.

6. Conduct Compression Test

• Remove the spark plugs and insert the compression tester into each cylinder.
• Crank the engine and record the readings; compare with manufacturer specifications.
• If any cylinder shows low compression, further investigation into internal engine components may be required.