how to fix P0301 misfire code in BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shock.
• Allow the engine to cool completely before beginning work.

2. Replace Spark Plug and Ignition Coil

• Tools Required: Socket set, torque wrench, dielectric grease
• Remove the engine cover if applicable.
• Disconnect the ignition coil connector for cylinder 1.
• Remove the ignition coil using a socket wrench.
• Remove the spark plug from cylinder 1 using a spark plug socket.
• Inspect the old spark plug for wear; replace it with a new one, ensuring it is gapped correctly according to specifications (usually 0.030 inches).
• Apply dielectric grease to the ignition coil connector to prevent moisture ingress.
• Install the new ignition coil and reconnect the connector.
• Torque the ignition coil to the manufacturer's specifications (typically around 10-15 Nm).

3. Inspect and Test Fuel Injector

• Tools Required: Fuel pressure gauge, multimeter (if necessary)
• Disconnect the fuel injector connector for cylinder 1.
• Use a multimeter to measure the resistance of the injector; compare it to specifications (usually around 12-16 ohms for standard injectors).
• If the injector is faulty, remove it using a fuel injector puller or appropriate tools.
• Replace with a new fuel injector and reconnect the harness.

4. Compression Test

• Tools Required: Compression gauge
• Remove the ignition coil and spark plug from cylinder 1.
• Insert the compression gauge into the spark plug hole.
• Crank the engine and record the compression reading; it should be within the manufacturer's specified range (usually 140-200 psi).
• If the compression is low, further investigation into the piston rings, valves, or head gasket may be necessary.

5. Check for Vacuum Leaks

• Tools Required: Vacuum gauge or smoke machine
• Inspect all vacuum hoses and connections around the intake manifold for cracks or loose fittings.
• If available, use a smoke machine to detect leaks in the intake system.
• Repair or replace any faulty hoses or connections.