By bad smell I take it that you are noticing a smell in the car while driving and not from the rear of the car. I'll also assume that the smoke is coming from under the hood and not the tail pipe. Sounds like you have an oil leak around the top of the engine that is dripping onto the exhaust pipe. I recommend that you clean the engine compartment with a good degreaser like Purple Power or Super Clean. Spray the entire engine down, everywhere you can. Let the degreaser sit for 10-15 minutes and rinse off with a strong stream of water. Repeat as necessary until the engine is free of visible grease and oil. Then buy some engine oil UV dye
and put that into the engine oil filler. Save some for the power steering pump (about 10th of a bottle is enough). Get some UV Glasses and a light used for detecting air conditioner leaks. Run the car for 15 minutes down the road. Stop and look for the florescent dye trails to find your leak. This is the hardest part of fixing this problem. After the leak is found the repair is usually minor.