If you notice a smell when you stop and are not sure exactly where its coming from, then try parking on a hill facing downhill. Since parking level may not help. obviously due to physics, when stopping, things are pushed forward. Maybe parking on a hill facing downward will reproduce the smell and indicate where the leak maybe coming from. Or try backing your car onto jacks. if anything, make sure the cars full of gas. if its almost empty, it may not reproduce the desired effect as the level in the tank might be to low. This is just a guess and I may be way off.