I have noticed that some gasolines have a higher sulfur content and during heavy acceleration you can smell the sulfur odor in your Crossfire's exhaust. I haven't noticed this with Shell fuel in my area. However, Shell got in lots of trouble in Florida because some of the gasoline they were selling there had such a high sulfur content that it was ruining fuel gauges in cars. The quality of your fuel is often greater impacted by which refinery it came from then what brand it sells under.