Abstract: A method and apparatus for hot testing on a production basis, automobile engines as they come off the assembly line for performing a final check on such engines before they are installed in the automobile. The engines are tested for exhaust emissions at three points or KEY MODES of operation at which emission related engine malfunctions are most likely to appear. These points of operation are high cruise, low cruise, and idle. The engine, after it comes off the assembly line is placed in a production test stand wherein the connections for water, oil and exhaust are made, the engine is started, accelarated to the high cruise speed, and allowed to warm up for a predetermined time, after which time, measurements of hydrocarbons and carbon monoxide are taken and an appropriate indicator light lit to indicate that the engine either is within limits at this speed, or does not pass for some reason. The same procedure is followed in the low cruise and idle speeds.