updates /
How to Test a Spark Plug To See If It's Working (DIY)
Introduction
Spark plugs are found in all gasoline engines. Their job is to ignite the air/fuel mixture inside the engine with just the right timing. Age, use and poor fuel quality can all contribute to a spark plug that's dirty and doesn't spark properly.
Failure to start or hard starting are two symptoms of a bad spark plug, as is rough running, higher fuel consumption and less power than usual. Learning to test a spark plug is a basic part of troubleshooting any small engine. The job takes just a few minutes and costs little or nothing.
How spark plugs work
- Spark plugs are always located at the top of the cylinder head of small engines. Cylinders like these have cooling fins on the outside and are one of the largest parts of any small gasoline-powered engine.
- All spark plugs thread into a hole in the cylinder head.
- A thick wire and fitting pushed over the end of the spark plug delivers the electric power needed to make the hidden tip of the spark plug spark.
- The ignition system of the engine sends a pulse of very-high-voltage current through this wire and into the spark plug — typically 20,000 to 30,000 volts for a small engine.
- The tip of the plug sits just inside the combustion chamber of the engine in the cylinder head and includes a small gap.
- When high-voltage electricity encounters this gap, it jumps the air space on its way to complete the circuit by flowing into the engine block. This jumping creates a visible spark that ignites the air/fuel mixture inside the engine so it can run.
- All problems with spark plugs boil down to a handful of deficiencies that prevent or impair electricity from jumping the all-important spark plug gap.
