What does a timing light diagnose?

A timing light is a diagnostic tool specifically designed to assess the ignition timing of an engine. It operates by emitting a beam of light that can be synchronized with the ignition pulses from the ignition system. When connected to a spark plug wire, the timing light flashes each time a spark occurs, allowing the mechanic to see the timing marks on the engine's harmonic balancer or timing cover. This visual feedback enables the technician to quickly determine whether the ignition timing is set correctly according to the manufacturer’s specifications.

By using the timing light to monitor the relationship between the ignition event and the position of the piston, mechanics can adjust the timing if necessary. This adjustment is crucial for optimal engine performance, as incorrect timing can lead to issues such as reduced power, fuel efficiency, and even engine knocking.

In comparison, assessing the air-fuel mixture ratio involves other diagnostic methods, while engine temperature can be gauged with temperature sensors or gauges. Compression levels in the cylinders are typically evaluated using a compression tester, making these options unrelated to the specific function of a timing light.