Into a bowl sift together the flour, the baking powder, and the salt. Set aside. In the medium bowl of an electric mixer beat together the egg yolks, the milk, and the oil until well combined. Gradually add the flour mixture, a little at a time, beating after each addition just until smooth. In a small mixer bowl, with cleaned beaters, beat the egg whites until stiff peaks form. Using a rubber spatula, genly fold the egg whites into the batter just until combined. Stir in the pecans.
For each waffle, pour about 1/4 cup of the batter into the center of the lower half of a preheated waffle iron until it spreads 1 inch from the edge, lower the cover, and cook according to the manufacturer's directions, or until the waffle iron stops steaming. Do not raise the cover during baking. Carefully loosen the edge of the waffle with a fork and remove. Serve hot.