how to fix P0304 code in BMW 3 Series E90/E91 (2005-2012) for cylinder misfire?

BMW 3 Series E90/E91 (2005-2012)

Error Codes

2-4 hours

Time

medium

Difficulty

medium

Severity

Error Code: P0304

3 min read

570 words

Problem Statement

The P0304 code indicates a cylinder 4 misfire in a BMW 3 Series E90/E91 (2005-2012). This issue can lead to poor engine performance, increased emissions, and potential engine dama

Error Code

P0304

Estimated Time

2-4 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical systems.
•Allow the engine to cool before opening any components to prevent burns.

Symptoms

•Check engine light illuminated
•Rough idle
•Loss of power during acceleration
•Increased fuel consumption
•Possible engine stalling
•Unusual engine noise (ticking or popping)

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0304 and check for any related codes.
2
Inspect the ignition coil and spark plug for cylinder 4 visually for signs of damage or wear.
3
Perform a compression test on cylinder 4 to check for mechanical issues.
4
Check fuel injector operation for cylinder 4 using a noid light or multimeter.
5
Inspect vacuum lines and intake manifold for leaks that could affect cylinder performance.
6
Examine the engine control unit (ECU) for any software updates or malfunctions.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•Remove the engine cover if necessary.
•Unplug the ignition coil connector on cylinder 4.
•Remove the ignition coil by unbolting and pulling it out.
•Remove the old spark plug using a spark plug socket.
•Install the new spark plug and torque it to the manufacturer's specification (typically 15-20 Nm).
•Reinstall the ignition coil and reconnect the electrical connector.

Parts Required

•Spark plug (for cylinder 4)
•Ignition coil (if faulty)
•Fuel injector (if faulty)

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Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0304 and check for any related codes.
2
Inspect the ignition coil and spark plug for cylinder 4 visually for signs of damage or wear.
3
Perform a compression test on cylinder 4 to check for mechanical issues.
4
Check fuel injector operation for cylinder 4 using a noid light or multimeter.
5
Inspect vacuum lines and intake manifold for leaks that could affect cylinder performance.
6
Examine the engine control unit (ECU) for any software updates or malfunctions.

Solution

1. Preparation

Gather all necessary tools and parts.
Disconnect the negative terminal from the battery to prevent electrical shorts.
Allow the engine to cool down before starting work.

2. Replace Spark Plug

Tools Required: Socket set, torque wrench, spark plug socket
Remove the engine cover if necessary.
Unplug the ignition coil connector on cylinder 4.
Remove the ignition coil by unbolting and pulling it out.
Remove the old spark plug using a spark plug socket.
Install the new spark plug and torque it to the manufacturer's specification (typically 15-20 Nm).
Reinstall the ignition coil and reconnect the electrical connector.

3. Inspect and Replace Ignition Coil

If the spark plug was fine, inspect the ignition coil for any cracks or carbon tracking.
Tools Required: Socket set, torque wrench
Remove the faulty ignition coil and replace it with a new one, ensuring it is seated properly and secured.
Torque the coil mounting bolts to the specified value (usually around 10 Nm).

4. Check Fuel Injector

Inspect the fuel injector for cylinder 4 for clogs or damage.
Tools Required: Fuel injector tester, multimeter
If the injector is faulty, remove the fuel rail and replace the injector.
Reattach the fuel rail, ensuring all connections are secure.

5. Verify and Reassemble

Reconnect the battery terminal.
Start the engine and allow it to idle, checking for smooth operation.
Ensure all components are reinstalled correctly, including any engine covers.