Chrysler Repair: 93 Concorde 3.3 -Poor gas mileage, fuel air mixture, poor gas mileage

Question
I have a 1993 Concorde with the 3.3 v6.  I am getting very poor gas mileage - in the 14 to 15 mgp range.  I am not expecting to get 25+ but I would think that I could get 20.  The car runs fine, no missing or or stumbling noted. There are no stored codes in the onboard diag noted. I have replaced the air filter, plugs and plug wires.  I am assuming that this is a fuel / air mixture issue, but since there are no codes I am not sure which sensors, I should be checking. Could a vacuum leak cause this?  Any suggestions as to what to check would be appreciated.

Answer
Hi Bruce,
I would believe that the fault code self-diagnostic would give you a code if it were the fuel/air mixture. I assume that you do get a 55 code, correct?
Absent any specific codes, you might think about frictional resistance such as dragging brakes (feel wheels after a trip) or under-inflated tires. A fuel leak might also be present. How about engine compression/oil burning as signs of general inefficiency of the engine? Unless you get a fault code, I can't identify anything in the engine that would cause lower fuel economy.
Roland