Cylinder 4 Misfire Detected
P0304 indicates that the engine control module (ECM) has detected a misfire in cylinder 4. A misfire occurs when the air-fuel mixture in the cylinder fails to ignite properly, causing a loss of power, increased emissions, and potential damage to the catalytic converter. Common causes include faulty spark plugs, ignition coils, fuel injectors, or low compression. The severity ranges from minor drivability issues to serious engine damage if left unaddressed.
01. Most Common Causes
- Faulty spark plug or ignition coil on cylinder 4
- Clogged or leaking fuel injector on cylinder 4
- Low compression due to worn piston rings or valves
- Vacuum leak affecting cylinder 4
- Engine control module (ECM) or wiring issue
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine misfire or rough idle
- Reduced power and acceleration
- Increased fuel consumption
- Engine vibration or shaking
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Inspect spark plug and ignition coil on cylinder 4; swap with another cylinder to see if misfire follows.
Step 3: Check fuel injector operation on cylinder 4 using a noid light or multimeter.
Step 4: Perform a compression test on cylinder 4 and compare to other cylinders.
Step 5: Inspect for vacuum leaks using a smoke machine or propane enrichment.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with a misfire, as it can damage the catalytic converter and cause further engine issues. If the misfire is severe, have the vehicle towed to a repair shop.
How much does it cost to fix?▼
The cost varies depending on the cause. Replacing a spark plug or ignition coil typically costs $50-$150 per part plus labor. Fuel injector replacement can be $150-$400. Compression repairs can be significantly more.