The OK Spark Fuel Injector Tester, No. 100090, allows the users to instantly check and diagnose the fuel delivery system, without removing any components from the vehicle. The Fuel Injector Tester uses a flexible replaceable probe to reach into the engine and read the pulse at the injector body or off the fuel rail. The probe allows user to access the fuel delivery system quickly and easily, keeping hands free from hot or moving engine parts. With a mechanical signal coming from the body, a sound and LED bar graph indicate when there is a problem. Waterproof storage case and 9V battery included.