As a result of the 1990 Clean Air Act Amendments, the use of oxygenated and reformulated fuels has already occurred in many metropolitan areas across the United States. Oxygenated gasoline contain oxygen carrying compounds (usually ethanol or MTBE) that chemically enleans the AT mixture. This leaner AT mixture results in lower carbon monoxide (CO) emissions from the tailpipe.
A few points require clarification concerning oxygenated fuels. First, late model feedback control vehicles may see a slight fuel economy loss (around 2%) when using oxygenated fuels. This occurs as a result of feedback system enrichening the mixture when the O2 sensor detects the additional oxygen provided by the fuel. Second, fuel system components in older model vehicles may experience swelling (hoses, O-rings, gaskets, etc.) from the alcohol used in some oxygenated fuels. The Owner's Manual contains detailed information on the allowable percentages of both MTBE and ethanol.
Emission Control Sub-Systems
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