In covered grill arrange medium hot coals around a drip pan. Test for medium heat above pan. Place ribs on grill rack over drip pan but not over coals. Lower grill hood. Grill for 1 hour. Prepare sauce: In a medium saucepan cook onion and garlic in hot oil till tender. Stir in tomato sauce, brown sugar, lemon juice, worcestershire sauce, mustard, celery seed, 1/2 cup water and 1/4 teaspoon pepper. Simmer for 15 minutes, stirring occasionally. Brush ribs with sauce. Grill ribs about 30 minutes more or until well done, brushing occasionally with sauce. Pass remaining sauce with ribs.