Got a 91 that came from the factory as a mulit-fuel (gas and CNG) set-up. It's never had an air pump installed. Was getting ready to replace the serpentine belt and not sure if it a stock size since it doesn't have the pump. Does the airpump use the flat side of the belt or the grooved. Mine has an idler wheel (mounted on the area where the pump should be) that runs on the flat side of the belt. That may allow a standard belt, but not sure. Has anyone seen this type of setup before?