The recommended practice applies to a production dynamometer test procedure which can be used to measure the smoke and gaseous emission characteristics of vehicular diesel engines. This procedure describes the smoke emission test method, smoke test cycle, gaseous emission test method, gaseous emission test cycle, equipment, instrumentation, calibration, data analysis, and correlation of results for comparison of production engine emissions performance to the requirements of the Federal regulations. Variations in engines, instrumentation, and test equipment may require modifications to these procedures or data reduction methods. The acceptability of this procedure is dependent upon documented statistical data appropriate to correlate all tests, data reduction techniques, and special instrumentation to the required Federal tests. When using the audit test procedure to assess the emissions performance of production engines, considerations should be given to expected emissions deterioration factors and quality control limits should be adjusted accordingly.