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The Coordinating Research Council (CRC) Intake Valve Deposit Group is evaluating a dynamometer based test to rank fuels for their relative tendency to form intake valve deposits. The Ford 2.3L OHC, dual spark plug equipped engine was previously selected (1*) for use in the current test program to determine optimum test conditions. A fifteen test design of experiments was constructed to reproduce intake valve deposit weight and morphology, representative of that causing field driveability problems. Test results were analyzed and a two-mode composite test was deduced from deposit weights, visual ratings, observations on the test valves and thermogravimetric analysis (TGA) results. Once the test was optimized, an additional ten test matrix was conducted to assess both repeatability and the performance of the test over a range of deposit levels. Base fuel and base fuel + two additive combinations were tested to provide a range of deposit tendencies.

As a vehicle accumulates mileage, deposits begin to build up in the intake system. These deposits, especially those on the intake valves, may cause poor cold start driveability, losses in power and fuel economy. Modern gasolines have multi-functional additives to provide all-around performance in areas of detergency, corrosion inhibition, stability, etc. Some of these gasoline additives may inadvertently cause unusually high increases in intake valve deposits and adversely affect the octane requirement of the engine. Dynamometer engine test procedures have been developed to evaluate the performance of gasoline additives in these areas. This paper describes the details of the test procedures, their repeatability and typical test results.