Hello all and thanks for all your input on this, 2006 GC with stow and go, SXT 3.8 with 127K miles. terrible fuel mileage, New plugs about a year ago, purrs like a kitten, I do have a bad fuel tank as liquid fuel is entering the emission system when the tank is full through the venting valve to the vapor canister, so I just never fill it up all the way. But I have not heard weather or not this would cause such bad fuel mileage 10.2 city, I might as well get a 2500 truck. no CE light to pull codes, is there still a such thing as a soft code? where the light does not come on? I am just going to be poor, well really already am. air filter is good, cleaned the throttle body really good about a week ago, Used two bottles of fuel system and injector cleaner. Not sure where to look next? Thanks folks, I Appreciate it.

 

The rule of thumb I've always heard is that the O2 sensor is good for 100k. That doesn't mean it rolls over and quits but it slowly loses it's effectiveness and kills the mileage. If you don't think the front one has ever been changed, I'd start with that.
The next thing that comes to mind is if the transmission is shifting through all of the gears and that the tires are the original size since changing sizes can affect the indicated fuel economy although not necessarily the real figure.

 

Thanks Mfahey, I will give it a try, I have the new sensor,

 

Changed out the 02 sensor this morning, The old one coming out is nearly white in appearance, I will post again when I get some Mileage data