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As automakers begin to develop and certify vehicles that meet the California Air Resources Board LEV II and Environmental Protection Agency Tier II Regulations, the study/usage of the Bag Mini-Diluter (BMD, or Mini-Diluter) sampling system continues to increase. Previous papers have provided an overview of the BMD and compared the measurements from the BMD to the measurements from a traditional constant volume sampler (CVS). These papers have suggested that the BMD approach offers new opportunities to improve the quality of vehicle exhaust measurement at very low levels, which will be crucial for accurate measurements on vehicles meeting LEV II SULEV standards (NMOG = 10 mg/mile, NOx = 20 mg/mile). This paper continues the effort to study and implement the BMD sampling system as the optimal sampling system for SULEV measurements. Based on the results from previous testing, a number of investigations have been initiated to improve the quality and understanding of BMD measurements.