My 2005, with 85k on it is getting very poor mileage. We were getting about 16 mpg, but after replacing the plugs (dealer did it, and had to remove the cab to do so), we then burnt a catalytic converter (apparantly from the oil they used to loosen the plugs), so we replaced that, and now we are getting 13.5 mpg. It has a K&N air filter, and we are running synthetic oil. Tire pressures are good (33psi cold).

Any suggestions? I am thinking of replacing the fuel filter, but I doubt that would create the poor mileage.

 

I have a 2005 5.4 4x4 with 110,000 miles and get 13.5 city-16.5 highway.
I changed my plugs at 80,000 miles.

 

Thanks Carlos. We were getting much better mileage than we are now. I wonder if the other coverter could be toast.

 

I have a 99 4x4 exp and I added a cold air intake by Airaid and a Gibson exhaust. After doing that my mileage just got worst! City driving must be below 10m to a gal. We don't take it long distances so I can't measure the hwy driving. I think the mass air flow sensor might be the issue. But I don't know. I have to work on the brakes this weekend.

 

I have an 05 Expedition 4x4 5.4V8. I have always gotten about 14. On the highway, I have gotten up to about 19 MPG. I went from the Contitrack (spelling) tires that came with the truck to the Michellin LTXs and lost about .5 MPG. I just installed a Volant cold air intake and Gibson cat back exhaust just hoping to get better mileage. The only way I could imagine getting 16 mpg would be if I was spending a fair amount of time highway driving. Could your commute have changed?

 

Well my wife drives it daily and we just do local city driving in it. I just paid for the 100k tuneup (spark plugs only) and change of oil. I'll measure the gas mileage once I fill it up.

 

Did you disconnect the negative battery cable after installing the intake and exhaust? I'm no expert here, so forgive me if I get this wrong. My understanding is - this will put the computer back in learning mode. Your engine should breathe a lot better now. The computer will need to figure that part out. You should disconnect the cable for at least one hour, then simply reconnect it. Once you do, the computer should relearn how the engine breathes. You will likely see some improved performance too.

 

Well I bought the intake kit and exhaust back in 2000 and installed it that weekend. I can't remember if I did or did not disconnect the grd cable to the battery. Now I have replaced the battery and the alternater since then. I also added a sound system which the stereo guys did have the grd cable disconnected for some time. I can't tell you if the computer has changed my gas mileage. But I can honestly say that I did get better gas mileage when everything was stock!

 

I just installed the exhaust system on my truck. It's too early to tell if my gas mileage will change. It will take a tank or two of gas before i know. My Expedition drives better - stronger and no problems with throttle response. I hope my gas mileage doesn't get worse. Good luck

 

Well, I changed the fuel filter, rotated the tires, cleaned the K&N airfilter, changed the oil (synthetic), changed the PAS fluid, and we are back to 15 MPG. The car is running much smoother, so it could have been a filter issue.

Our commute did not change much but we are driving slightly more secondary streets.

 

You might try cleaning your MAF sensor also.

 

Sheesh, you just can't please anyone these days.

 

I know, I know, but it just might get him back that 1 mpg he's still missing.

 

What truck and engine do you have? 4x4 or 4x2?

 

My expedition gas mileage has dropped down to 13 mpg recently. I Took several of the suggestions here.

1) Put 33 psi in the tires
2) check all the spark plug wires for wear. Cleaned them with brake cleaner spray.
3) Pulled out the Mass airflow sensor and shot it with compressed air and brake cleaning spray.

Took if for a 25 mile drive. 4 miles in the city and the rest on the highway. Mileage started going up. when I got back home and parked it the mpg was 18.9. Don't know what fixed it but think it was one of these three.