i have an 05 pacifica. the other day i backed the car out of the garage and noticed the exhaust smelled worse than it use to.it smelled like rancide gas with a strong exhaust smell. ive also noticed the mpg has gone down. there are no check engine lights on.and i have recently replaced the spark plugs.should i be concerned or not worry about it?

 

Maybe O2 sensors? Something messing up the A/F? How's the performance? Maybe get a buddy to drive behind you while you run it at WOT and see if it smokes at all... If you have an emisions or sensor issue, it should throw a code soon.

Also, any indication of a mis-fire? Rough idle? I doubt this is related to a spark issue but, ya never know.