One problem related to fuel pump has been reported for the 1999 Mercury Mystique. The most recently reported issues are listed below.
There is a constant gas smell during the winter time. The smell is worse right after filling the car with gasoline and anytime the car is started more than one time such as needed to take care of errands. The smell is so bad at times I am afraid to leave the car close to the house. I have reported this many times and the fuel pump was supposedly checked and the fuel filter replaced at one point. Gasoline has leaked at times from behind the passenger side front wheel. This happens during the winter months for the most part.