TRUNK SEAL<<<<<<<<
when i got my old 69 charger, the guy said, in the 9yrs he had it he could never figure out the exhaust smell in the car, his wife and daughter would never go in the car with him, and he had 200 air fresheners in the car all over, bounce sheets under the seats. Shortly after getting the car i noticed that driving with the windows up was fine, then as soon as i cracked the window open it was instant exhaust fumes
Sure enough changed the trunk seal and it was totally gone. When you open the window you effectivly create a low pressure in the car, and exhaust fumes are tumbling behind the car, if there is a low pressure in the car, the fumes come into the car from the trunk seal.....