Abstract: Modal test method and apparatus is described for use in automotive engine plants, vehicle inspection stations, diagnostic centers, etc., for quickly, accurately and repeatably measuring the principal air contaminants; i.e., carbon monoxide (CO) and hydrocarbons (HC) in engine exhaust gas emissions. Quantitive measurement of oxides of nitrogen (NO.sub.x) and oxygen (O.sub.2) may also be measured if desired. While O.sub.2 is not an air contaminant, a measure of its concentration in the exhaust gas has diagnostic value. The engines are tested at prescribed modes of operation (usually three; high cruise, low cruise and idle) at which emission-related engine malfunctions, if they exist, are most likely to be exposed. CO and HC (NO.sub.x and O.sub.2 if desired) evaluations are made at each test mode and may be recorded on a "report card." The measured test values of the air contaminants are compared at each test mode with prescribed permissible values either automatically or manually.

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.