WL-136 DUOYI DY28 Spark Plug Tester is a device used in the automotive industry and is designed to test the working condition of engine spark plugs. This device is used to measure the ignition performance of spark plugs and to detect faulty spark plugs. The DY28 model is generally simple to use and offers a quick and effective solution for the detection of faulty spark plugs. The device determines whether the spark plugs are firing properly by measuring the voltage and ignition power applied to the spark plug.