A pulse detonation engine were operated in continuous mode, and a state were identified where the media in almost all of the pulses detonated. In contrast to what is common, this engine utilizes injection of fuel/air through several ports along one side of the engine, and for the state were the media detonates there is a short "delay time" (a few seconds) before the pulses detonates. The reason for this behavior is not clear, but it correlates well with the temperature in the engine. A system using estimates of the speed of the combustion front between different positions along the side of the engine were used to determine whether the engine detonated or not. The conductivity between the electrodes on ordinary spark plugs were used to determine the arrival of the front to the different positions.