Engine Misfire Causes: Rough Running Explained

Introduction

A misfire feels like a stumble or stutter in the engine. It happens when one cylinder doesn't fire correctly.

Causes

• Bad Spark Plugs: The most common cause.
• Faulty Ignition Coils: Common in Fords and Hyundais.
• Vacuum Leak: Too much air entering the engine.
• Fuel Injector Issue: Clogged or dead injectors.

Fix

Replace spark plugs every 60k-100k miles. If you have a code P0301, swap the coil from cylinder 1 to 2 – if the code moves to P0302, you found the bad coil!

Cost

Set of plugs: $50. One coil: $60-$120.