2003 Mitsubishi Eclipse Check Engine Light-Code for Excessi

Recently our 2003 Mitsubishi Eclipse has been displaying the "Check engine light". Each time my husband takes it to Advanced Auto to read/clear the code, they tell him the code is reading Excessive Fuel Loss. The gentleman told my husband today that it could be because he wasn't tightening the gas cap when he fueled up. We always tighten the cap. What other items could cause "Excessive Fuel Loss". We've recently replaced the seals (associated with tie rods), inner tie rods and the suspension bars or whatever they are called.