Spark plugs that fire in open air may not necessarily fire under compression. This is due to increased operating pressures within the cylinder that are not present in an open atmosphere.

This means that, even if your spark plug fires outside the cylinder, it may not fire while inside. Seeing the spark plug firing outside the cylinder gives the trouble-shooter a false sense of certainty that the spark plug is trouble-free. If you can tell that the spark plug is firing under compression, then you will know definitely that the problem is fuel related.

Knowing that there is high voltage present does NOT guarantee that the spark plug fired inside the cylinder.

The OK Spark® Spark Plug Sensor will indicate that both high voltage is present AND that the spark plug is firing under compression. The indication of this information is simultaneous and immediate. This is the only handheld microcontroller-based tool in the market that does this.

OK Spark® Spark Plug Sensor is the fastest indicator of real spark activity under compression in the market. There is no special training or knowledge required to use it. Simply bring the probe (included) near the spark plug boot and watch for the LEDs to light up. If not, then no spark occurred inside the cylinder.