Preheat over to 350°F. Lightly grease a 9 x 13 inch pan. In a large bowl, combine pumpkin, evaporated milk, eggs, sugar, salt and pumpkin pie spice. Mix well and pour into prepared pan. Next, sprinkle cake mix over the pumpkin mixture. Drizzle margarine over the cake mix and then sprinkle pecans over the top. Bake for 55 minutes or until done.