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


15-02-2026, 12:44. Posted by: carsoftos777



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


Repair Cost
Spark plugs $100–200
Coil replacement $150–350
Compression repair $1000+



Can You Drive?


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

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