How Engine Cylinders Work

• Air, which contains roughly 21 percent oxygen, is drawn into the cylinder and fuel is added. The air/fuel mixture is compressed and ignited by a spark from the spark plug. The process is typically straightforward, but if anything goes wrong this is known as a cylinder misfire.
  
  

Causes

• Cylinder misfire can be caused by lack of spark, lack of compression or imbalance in the air/fuel mixture. Lack of spark can be caused by worn or damaged spark plugs, lack of compression by a blown head gasket and imbalance in the air/fuel mixture by a faulty fuel injector, fuel pump or pressure regulator.
  
  

Diagnosis

• A steady or continuous misfire can be diagnosed by isolating each of the engine cylinders, in turn, by disconnecting the spark plug wires when the engine is idling. Intermittent cylinder misfire is more difficult to diagnose and may require a scanning tool or a digital storage oscilloscope.