Ford V10 gradual reduction in fuel economy

Try cleaning the MAF sensor. Easy to do, just buy the correct spray from the auto parts store. It's easy to check the O2 sensors, they should read out a certain ohm reading on your multimeter. Youtube has a video on it I'm sure.

New spark plugs and all new coil overs were installed at 100,000 miles but that did not help the mileage problem.

Have the spark plugs been replaced? If not, they're probably at (or beyond) the end of their useful life.

Oxygen sensors do age, and are relatively inexpensive and easy to replace. If they're only somewhat out of calibration they may not cause check engine lights but still affect mileage some (and possibly catalytic converter life), or so I've been led to believe. Replacing them might be a reasonable thing to try. For that matter, if the catalytic converters are getting plugged from soot or whatever, that can affect engine performance as well.

Hi whemme,

Check for this.......It is possible someone who worked on your rig made this easy mistake, causing poor fuel economy and poor performance. It is easy to check for.

Pop-off the oval air intake from above the radiator and pivot it upward. Look into the hole where it was snapped into. If you see a black plastic flap that interferes with the flow of air, you need to remove the black plastic shroud above the radiator and fold the flap back while resetting it into position.

There was a recall in 2010 on that flap. Apparently a new-bee line worker was not holding the flap back when installing the black plastic top radiator shroud. It is conceivable that an unsuspecting mechanic could make the same mistake. I almost made that mistake myself on our 2007 E350 when reinstalling the top shroud after removing a bird that died hitting and getting lodged into our front grille area.

PartyOf Five wrote:
We add a couple cans of seafoam periodically to clean the inserts but I'll be curious what you learn also.

Not sure what you mean by inserts. Do you mean injectors?

We add a couple cans of seafoam periodically to clean the inserts but I'll be curious what you learn also.