Search Results

Approximately 245 passenger cars were involved in a Cooperative Test Program (CTP) conducted by EPA and industry. The purpose of this program was to examine ways of improving the effectiveness of I/M tests, specifically for the 1981 and later vehicles with closed loop fuel metering. Detroit area vehicles failing the Michigan Auto Exhaust Testing (AET) program were recruited and investigated to determine the cause of the failures. Complete FTP emission tests were run as received, and at each step of the repair sequences. A variety of I/M preconditioning methods were evaluated to understand false failures. GM's portion of the CTP was sixty vehicles, half 1981-1982, and half 1983 and later model years. During the time period of the CTP, the AET failure rates were 14.5% for the 1981-1982 model years and 6.6% for the 1983 and later model years. Although all sixty vehicles had failed the Michigan AET, thirty-three (55%) passed “as-received” when tested in the 6M laboratory.

EPA and GM test programs have quantified the in-use emission performance of the GM closed-loop emission control systems. In-use exhaust emission levels, adjusted to the 50,000 mile point, show averages under the standards for the 1986 model year cars. In-use evaporative emission levels are under the standard, on average, for the 1985 and 1986 model year cars. Fuel injection systems have inherent evaporative emission performance advantages over carburetor systems. Average exhaust emission levels for the national fleet will continue to decrease as the closed-loop fleet replaces the older models. Predictions of future inventories are lower if the GM data reflecting the 1981+ emission improvements are used instead of the estimates currently in the MOBILE3 model.