99', 5.4L. Getting about 13 mpg in-town and 15 hwy. Used to get 16 in-town, 18 hwy. Aircleaner is spotless, PCV new, plugs (OEM)have 30K on them, I run Mobil 1 (since new) 5w-30 and change the oil every 3-5K. Any recommendations?

 

I would recommend a K&N FIPK, a tune (i.e Diablo Sport preditor tuner), exhaust....more air in and more air out the better the gas mileage.

 

I feel your pain. I have a 2005 EXP when first purchased got 16.9-17.2 MPG on a regular basis. At approx. 3000 mile engine started idling rough and mileage went to 9.6. Took it to dealer and they said, yes it is idling rough and they would investigate. After 3 weeks in shop and sending out a service engineer from back east, Ford claims everything is normal. What a laugh. The engine runs smoothe after Idle but milage is 10.0 indicated on dash and when measured, actual mileage is exactly what dash indicates. Ford claims they road tested the vehicle and thier instruments showed 17.5 MPG. They said because the vehicles computer was reset and the mileage indicated on dash was erroneous until 500-1000 MILES were put back on vehicle. Well you knew where that was going and WA-LA, MILEAGE IS STILL 10.1 INDICATED AND ACTUAL after 1500 more miles. I have heard of the individual spark plug coils going bad and that might be the cause of the rough idle, BUT there is no code showing this and Ford will not do a thing. At around $40.00 a piece it is not economical for me to do the testing. This coil problem although will not cause mileage to drop that much.

I have searched everywhere and cannot find any help for this.

Will someone please help?