Something smells

I ASKED Subaru's technical people for help and they replied: ``The rotten-egg gas smell is from the sulphur content in the fuel, which varies depending on the brand and grade of fuel used. It occurs when either the content of sulphur is high or when there is insufficient temperature in the exhaust catalyst to completely burn off the sulphur. Typically it occurs most often after a long trip and a short break, then a short trip, when the catalyst does not come up to full operating temperature. ``This type of gas generation is solely dependant on the sulphur content of the fuel. It may also be caused by incorrect operation of the exhaust catalyst. If you have tried many different grades and brands of fuel without effect, replacement of the catalyst may be required.''