Preheat oven to 350 degrees. Place pie crust in a 9-inch pie plate and flute edges. In a meduim bowl,combine Splenda,flour,maple syrup, and water. Add eggs,margarine and vanilla extract.
Mix well to combine. Stir in pecans and Grape Nuts. Pour mixture in pie crust. Bake for 45 to 55 minutes or until filling feels firm in center. Place pie plate on a wire rack and allow to cool completely.