1. Preheat grill to medium high. In a large ziplock bag, combine olive oil, garlic, chili powder, cumin, paprika, salt and pepper. Add lime juice and rub sides of bag together until mixture forms a thin paste. Add pork to bag, seal bag and rub sides well until spice mixture has coated pork thoroughly.
2. Just before cooking, oil heated grill. Remove pork from bag, place on grill and cook, turning occasionally with tongs, until a meat thermometer inserted in thickest part reads 140ºF, 15 to 20 minutes. Transfer to a cutting board, cover loosely with foil and let rest for 10 minutes before carving.