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In support of the regulations prohibiting the sale of devices which bypass or defeat automotive emissions control strategies, a study was undertaken to compare emissions generated from vehicles using original (OEM) and aftermarket programmable-read-only-memory (APROM) chips. Six different vehicles and chips from three separate APROM manufacturers were tested in this investigation. The driving cycles used in this work were the standard Federal Test Procedure (FTP) driving schedule and a cycle that closely resembled the California acceleration (CA) cycle. The test plan was based on running two OEM emissions tests, followed by two APROM tests, and then a final OEM test. The data were analyzed using an unpaired t-test to compare differences between means. Data for one vehicle was analyzed using a two way analysis of variance to separate driver effects from PROM effects. This was necessary due to the use of two different drivers during testing.

A Repeatable Car (REPCA) program has been developed at the Environmental Protection Agency's National Vehicle and Fuel Emissions Laboratory (NVFEL) as part of an ongoing effort to improve the precision of fuel economy and emissions measurements. This concept of using a repeatable car as an integrated system diagnostic tool is not a new idea in the emissions testing field; however, our statistical analyses and organizational approach may be different from what other laboratories are using. Furthermore, given the NVEFL's role in automotive emissions testing, we felt it appropriate to provide related industries a detailed account of our standard laboratory practices, both for informational and comparative purposes. In order to separate vehicle and measurement variability in a relatively simple manner, a process was developed to track REPCA data based on Statistical Process Control principles using the calculation of individual site offset values from two week moving averages.