Abstract: A timing gauge is provided for use in adjusting the stroke of a fuel injector plunger of an internal combustion engine. The gauge has a probe of calibrated length fixed to a magnet effective to clamp the gauge firmly to the outer end of the injector plunger while the plunger is being adjusted. When the plunger is adjusted until the probe contacts a reference surface, an electrical circuit containing an indicating device is activated to inform the mechanic that the plunger is in precise adjustment. The gauge may be self-contained and include the indicator and its power supply.