P0304 Misfire Code – Why Cylinder 4 Fails & How Mechanics Fix It

P0304 indicates misfire detected on Cylinder 4.

This is one of the most searched misfire codes because it appears frequently on 4-cylinder engines.

Symptoms

• Engine shaking

• Power loss

• Hard starting

• Fuel smell

• Rough idle

Main Causes

• Bad ignition coil

• Worn spark plug

• Fuel injector clog

• Compression loss

Professional Repair Flow

Mechanics usually:

1. Inspect plugs

2. Swap coils

3. Check injector pulse

4. Test compression

Repair Costs

Can You Drive?

Driving long-term is dangerous — catalytic converter damage may occur.