There's no faster way to detect fuel injector firing, even when you can barely see them. No hunting for the injector wires or upper plenum disassembly to test at the connector. The probe is specifically tuned to detect the vibration frequencies caused when the fuel injector pintle snaps open. Each time the injector opens the LED strobe flashes. Made in the USA, and backed by a Limited Lifetime Warranty The Model 76400 Electronic Fuel Injector Quick Probe has a super bright LED Strobe which allows you to visually monitor the injector pintle for consistent firing or misfires. Simply press the probe tip against the injector body and the bright LED strobe will flash with each time it opens. The battery operated main unit with removable 7" probe tip allows access to virtually any injector even if they are buried under the upper intake plenum.