Cream the margarine and 1 1/2 cup of sugar substitute until light and fluffy. One at a time, add the eggs, beating well at medium speed with an electric mixer after each addition.
In a separate bowl combine the flour, baking powder, soda, and salt, and then add it to the creamed mixture alternately with milk, beginning and ending with the flour mixture. Beat at low speed after each addition.
Cut the pineapple into 1/2 inch pieces and then fold it gently into the batter.
Spoon the batter into a 6 cup bundt pan or heavy ring mold coated with cooking spray.
Bake for 45 to 50 minutes.
Combine the pineapple juice and remaining sugar substitute until the sugar dissolves. Remove the cake from the oven and immediately pour the juice mixture over the cake.
Let the cake stand for 5 minutes before removing it from the pan.