A statistically designed fleet test was conducted to evaluate the effects of intake valve and combustion chamber deposits on vehicle performance and regulated tailpipe exhaust emissions. This test was run in twenty 1994 vehicles, powered by Ford 2.3L Dual Spark Plug engines. These vehicles were driven by trained drivers for 40,255 km (25,000 miles) on a specific test route to promote intake valve deposits. The test matrix included both reformulated and conventional gasolines, and three different gasoline additive technologies. Also evaluated were the deposit effects on octane requirement increase. In addition, an attempt was made to correlate the intake valve deposits from the field test with the current BMW 318i and proposed Ford 2.3L intake valve deposit tests.
This study showed significantly higher HC and CO emissions with the untreated base fuel. A directional increase in NOx emissions was observed with increased combustion chamber deposits. While significant differences were noted between additives for combustion chamber deposits, there was no correlation between these deposits and octane requirement increase. There was a strong correlation for the intake valve deposits observed in the field with the BMW 318i, and the Ford 2.3L.