A vehicle test program has been conducted to determine the effects of certain aspects of fuel composition and detergent additives on the formation of deposits in multiport fuel injectors (MPFI). Eight identical vehicles were tested on programmed mileage accumulation dynamometers using a repetitive short-trip/hot-soak driving cycle and a base fuel with “which deposits were produced. As part of the program, the base fuel composition was changed, and a variety of detergent additives were tested in the base fuel.MPFI deposits increased with increasing olefin (particularly diolefin) content of the fuel, were unaffected by aromatic content of the fuel, and were not appreciably affected by the addition of alcohol. Also, several commercial detergent additives now available delayed or prevented deposit formation in port fuel injectors. Oil companies have been strongly encouraged to use these or similarly effective additives to improve the quality of all grades of gasoline and ensure compatibility with present and future fuel metering systems.