Mix together salt, pepper and sugar in a small bowl.
Rub ribs on both sides with salt mixture.
Place the ribs in a large roasting pan and add the orange juice and water. Tightly cover with foil. Place in oven and roast for 6 hours.
Remove the ribs from the oven and uncover. Remove from braising liquid.
To prepare BBQ sauce: Heat a medium sauté pan on medium high heat. Add onion and cook until translucent. Add ketchup, mustard, brown sugar, molasses, Worcestershire, salt, and cayenne. Reduce heat to low and simmer for 1 hour. Remove from heat and add to blender. Blend well.
Preheat a charcoal or gas grill to medium high heat.
Transfer the ribs to the hot grill. Brush the ribs with the sauce, and baste and turn every 5 minutes.
Remove ribs from the grill. Serve with additional sauce on the side.