Joined: Dec 2007
Location: New Smyrna Beach
Well this is a huge problem as that car should be getting closer to 19-22 mpg (thats taking into consideration the combination of heavy foot and in town and highway driving).
You said you changed plugs, what plugs did you buy? Did you gap them correctly? Did you change the plug wires? What plug wires are on it? When you changed the air filter did you take off the air intake from the throttle body and clean the throttle body plate? Did you change the fuel filter as it is most likely original? What octane fuel do you run in the car?
Sorry for the 20 question game but figured it saves us a lot of posting back and forth to try and figure things out better...
Have you heard of a product called seafoam? Walmart and almost all Auto parts stores sells this product. Basically start up car with the power brake booster vaccuum line unpluged off the booster which will obviously cause the car to run rough and have a huge vaccuum leak. Slowly let the seafoam get sucked into that vaccuum hose (might need someone to help throttle the car upto around 1200 - 1500 rpms to keep it running) allow the whole can to get sucked thru the line then shut the car off for about 10 minutes. Reconnect vaccuum line and start it up hitting the throttle pretty good to help blow the rest of the smoke and carbon burn-off thru the exhaust system. (Make sure you do this about once every 3 months)
This should help bring that mpg number up alot and make the car run alot smoother as well.
2003 Mustang GT Convertible 5 speed - Mostly stock 4.6... 455 rwhp and 573 ft/lbs torque. (SOLD due to divorce)
Currently working on Coyote Swap of a 2004 GT