Grilling a whole pork loin requires little more than patience. It's a thick cut of meat, and to ensure that it is properly cooked you need to use medium heat. This helps guarantee that the outside of the loin doesn't burn before the inside is thoroughly cooked. Marinating the pork loin for at least 12 hours also helps ensure that your seasoning gets infused throughout the loin, which makes for a more flavorful end product.
In a small bowl, mix the salt, paprika, sugar, cumin, olive oil, chili powder and garlic. Rub the mixture all over the pork loin. Cover the loin and refrigerate it for 12 to 48 hours.
Preheat the grill until an oven thermometer sitting on the grill grate reads 450 degrees Fahrenheit. Push the coals to one side of the grill, so that you have one cooking area directly over the heat and one away from the coals.
Lightly oil the grill grates and place the pork loin directly over the coals. Cover the grill and cook the loin until it begins to brown and can be moved without sticking to the grate. This should take about five to 10 minutes.
Flip the pork loin over and place it on the area that is not directly over the hot coals. Cover the grill and cook for another hour, or until a meat thermometer inserted into the center of the pork loin reads 145 degrees Fahrenheit. During the cooking process, check the grill every 15 minutes to ensure that the cooler side of the grill is 350 degrees Fahrenheit. If the temperature drops, it may be necessary to add more coals.
Remove the pork loin from the grill and allow it to rest for 15 minutes before cutting.