05 GT Conv fuel issue
 

My 05 GT (106,000 miles on it) used to get 18-20mpg. In the last cpl mths, fuel has dropped to 11-12mpg. This week it dropped to 7-8mpg. Have had it in the shop 4 times. Tune up, oil &. fuel filter change. Diagnostics run. They cannot seem to find a reason for this. Thought maybe it was a faulty fuel filter since this began right after having it changed. New filter installed and now it continues to drop mpg.

Any ideas or suggestions??
Please help!!

I believe your vehicle has a capless fuel system. If that system is not sealing properly guess where your gas could be going. If it goes out that way at certain times when the evap monitor is not running no code will appear to indicate any problem.

Thank you Hanky for answering. Do you mean the fuel cap? I was scheduled to take to the dealer on Thursday for another diagnostic. But as you said, they never read anything as a problem. So I really dread taking it for yet another. Perhaps I should try a new fuel cap? And no it is not a capless fuel system.

If it doesn't have a capless system, , it should pick up a leaking fuel cap.

Yea I would think it would. But I've diagnostic run 4 times already with no results. I appreciate your help. I think I will go tomo and get a new fuel cap and see if that makes a difference.