Which component is most directly assessed with a spark tester?

The spark tester is specifically designed to measure the presence and strength of the ignition spark produced by the spark plug in an engine. By connecting the tester in place of the spark plug, it allows the user to evaluate whether the ignition system is functioning properly and creating a spark capable of igniting the air-fuel mixture within the combustion chamber. A strong, consistent spark indicates that the ignition system is working correctly, while a weak or absent spark can signify problems with components such as the ignition coil, spark plug, or electrical connections.

Other components listed, such as throttle response, fuel injector function, and compression levels, are assessed through different means and tools. Throttle response pertains to how well the engine responds to throttle input, which involves fuel delivery and air intake but is not directly related to the ignition process. Fuel injector function requires testing methods that measure fuel delivery rates and injection patterns. Compression levels are determined using a compression gauge and assess the engine's ability to hold pressure in the combustion chamber, which is unrelated to the ignition spark itself. Therefore, the most direct assessment that a spark tester provides is for the ignition spark.