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Engine-Off Natural Vacuum (EONV) principles based leak detection monitors are designed to determine the presence of a small leak in the fuel tank system. It was introduced to address the ever more stringent emission requirement (currently at 0.02”) for gasoline engine equipped vehicles as proposed by the Environmental Protection Agency (EPA) and California Air Resources Board (CARB) in the United States [2, 3]. Other environmental protection agencies including the ones in EU and China will be adopting similar regulations in the near future. Due to its sensitivity to known noise factors such as the ambient temperature, barometric pressure, drive pattern and parking angle, it has been historically a lower performing monitor that is susceptible to warranty cost or even voluntary recalls. The proposed new model based monitor utilizes production pressure signal and newly instrumented temperature sensors [15].

An integrated model-based three-way catalyst control and diagnostic monitoring system is described which has the potential for improved health discrimination while also significantly reducing the calibration burden. The catalyst is modeled as a simple limited integrator with an adaptive integral gain. The adaptive gain, used in the control system, is also used as a diagnostic metric since (among other variables) it reflects the catalyst oxygen storage capacity and hence the health of the system. The method has been applied to a 4.6 liter ULEV II gasoline engine, and tested over an EPA Federal Test Procedure drive cycle with a number of differently aged catalysts. Preliminary results are encouraging, and show that the method is able to discriminate between the catalysts, even those with similar age near the OBD threshold.