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Three vehicle and dynamometer-aged converters were evaluated for performance using the warmed-up portion (termed the “hot-18” cycles) of the Federal Test Procedure (FTP) and during a steady-state cruise using low and high sulfur content fuel. During the steady-state tests the catalyst performance was also monitored using two oxygen sensors designed to satisfy Phase II On-Board Diagnostics (OBD-II) requirements for vehicles sold in California in MY 1994 and thereafter. The performance of two of the converters decreased significantly upon switching to the high sulfur content fuel, and one of the converters which was diagnosed as passing with low sulfur fuel was diagnosed as failing with high sulfur fuel.

The performance of the OBD-II catalyst monitor of a 2.2 Corsica TLEV was investigated while operating on fuels with differing sulfur levels. Testing was performed using a driving schedule producing operating conditions which were acceptable to the production OBD-II system for active diagnosis of catalyst performance. During each test, catalyst diagnostic data and emissions performance data were collected simultaneously. Tests were performed at 22° C using California Phase II (35 ppm sulfur content) and Indolene clear (470 ppm sulfur content) fuels, and at 4°C using a commercial oxygenated Winter fuel (320 ppm sulfur content). Four dynamometer-aged converters were using in the testing. Converter performance in the form of HC conversion efficiency was found to generally decrease when the sulfur content in the fuel was increased.