In a medium saucepan, combine maple syrup, chili sauce, vinegar, Worcestershire sauce, onion, salt, dry mustard, and pepper. Bring to boiling; reduce heat.
Simmer the mixture, uncovered, for 5 minutes or until slightly thickened. Set aside half (about 1/3 cup) of glaze. Use the remaining glaze to brush on the thick pork chops during grilling.
In a covered grill, arrange preheated coals around a drip pan for indirect grilling. Test for medium* heat above the drip pan. Place the chops on the grill rack over the drip pan. Cover and grill for 35 to 40 minutes or until juices run clear, turning once and brushing with maple glaze the last 15 minutes of grilling. Serve the remaining glaze with the chops. Makes 4 servings.
To test the temperature of the preheated coals, place your hand above the coals at the height the food will be cooked. Start counting and if you need to remove your hand after 4 seconds, the coals are medium.