An engine testing device for dynamic pressure loss and valve seal-tightness testing of a running four-stroke engine includes: a first pressure gauge detecting a pressure value in an air intake line to a cylinder of the engine and outputting a first output signal indicative of the pressure value detected; a second pressure gauge detecting a pressure value in an exhaust line of the engine and outputting a second output signal indicative of the pressure value detected; a trigger device detecting an electrical signal indicative of when a selected cylinder of the engine is the particular active cylinder; and a measured value detection device detecting the output signals of the first and second pressure gauges and an output signal of the trigger device, such that an association between points in time of the pressure measurements and the particular active cylinder is enabled.