Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch pan.

Make the cake: In a large bowl, sift together flour, sugar, baking soda, and salt. Add pineapple with juice and eggs. Mix at low speed until well blended. and pour batter into the prepared pan.

Bake in the preheated oven until a tester comes out clean, 30 to 35 minutes.

While the cake is baking, make the topping: In a saucepan, combine sugar, milk, and margarine. Bring to a boil and cook for 2 minutes, stirring constantly. Add pecans and coconut and mix to combine. Remove from the heat.

Remove cake from the oven. Immediately pour topping over the hot cake and spread to cover the surface.