Have a friend who just got a 2002 Expedition with a 5.4 and only 61K miles...it seems to be getting only 10-13 mpg though. I have never had one so I cannot say, but is that number correct? Anything we can do to make it better?

 

I've got a 2000 with the 5.4 and I get 12 city 15 highway, consistently for years now. I drive the speed limit mostly with the occasional quick acceleration when needed.

 

That seems quite a bit better than what this one gets....wonder what we need to do

 

Changed your air filter recently? Also in winter some states get really lame gas which makes mileage go down. Mine has 160,000 miles on it. Do you have a lead foot?

 

Its not mine, Im just helping a friend out since she doesnt know about vehicles. Id say she drives the speed limit but not over that. I will ask her about the filter....and being in missouri we have crap gas all year round thanks to the ethanol mandate. Now that I think of it, if I figure in the mpg loss with ethanol it would put hers right up there where yours is with good gas....hmmm she might be outa luck

 

I would still check the air filter... I started getting worse gas mileage and changed mine and it went right back to normal.

 

FYI - Like you I too used to think that a dirty air filter reduced MPG, but guess what...it doesn't. The way it was recently explained to me is any restriction caused by a dirty air filter only robs you of top end (high RPM) performance. The computer regulates the air/fuel mixture, so regardless of the amount of air flowing, the correct amount of fuel is added to it. The restriction from the dirt is only equivalent to not opening your throttle as far.

 

I don't know if I completely agree with that Alloro. A dirty air filter can reduce mpg. It's happened to me and actually a good quality air filter can increase mileage. Don't forget you will pushdown on the accelerator pedal, the TPS is then sending a signal that the throttle is opened and that also affect MPG. The computer is actually getting conflicting signals and trying to adjust it. Result- poor fuel economy.
Back on topic. Your right foot is the biggest reason why fuel mileage is usually decreased. My 2000 E. Bauer Expy - 5.4 loaded with every option, therefore, heavier than most, can get 18-19 mpg. Yes it does. That is at 55-57 mph, calm day, temps above 40 and easing on and off the accelerator. My driving involves small town (25 mph), stop signs, 2 lanes road w/stop signs. etc. Watch how you drive it. Slow to accelerate and if you don't have a line of traffic behind you, let off the gas 1/3 mile before stop signs and coast. It does help. Don't do the jack rabbit starts, that kills mpg quickly. Driving style is a lot of it. Of course, there maybe something actually wrong, an emergency brake dragging, brakes dragging, bad or under inflated tires or an engine that is getting tired. Just remember this is a 6000lb truck. Fuel economy was never a forethought for these trucks. Good luck.

 

I wasn't stating an option, I was relaying a fact, and since this thread is about MPG, then this is on topic.
Here's a report issued by the US Department of Energy.
http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf

Page 13 has the acceleration results of clean vs. clogged filters, while pages 14 and 15 have the MPG results.

 

Ditto on the MPG. As the TPS signals a larger throttle opening for the current RPM, the PCM figures the vehicle is under load, as in going up a hill or towing a heavy trailer, etc, so it pulls some timing from the ignition to prevent detonation - bingo! fuel efficency goes South. But the filter has to be really dirty to effect this at light throttle/loads.

I'd like to Double Ditto fordno1's right foot comments!

 

It's also winter, are you letting your car warm up before you start driving it? If you let it sit there for 5-10 minutes running every day that can appear to be low mileage because it's using gas but not going anywhere.