What does a spark tester determine?

A spark tester is an instrument used to assess the ability of an ignition system to generate a spark sufficient for combustion. It primarily evaluates whether adequate voltage is available to create a spark. When connected to the ignition system, the spark tester allows you to observe the spark produced and confirm that there’s enough voltage being generated to ignite the fuel-air mixture in the engine.

This assessment is crucial for troubleshooting ignition problems, as a weak or absent spark can hinder engine performance. By determining if the voltage is adequate, you can diagnose issues related to the ignition coil, battery, or spark plug, ensuring the engine can start and run properly.

In contrast, while a spark plug's functionality is important and can be part of the overall diagnostics, the spark tester does not directly test the spark plug itself but rather confirms the voltage from the ignition system. Similarly, the compression rate of an engine and the length of spark plug gaps are determined through different methods and tools, not with a spark tester.