Arvina

Hi guys. Long time lurker first time poster. I've searched plenty on this issue but I every situation is different and I like some advice on where to start looking first. I bought my 07 fx4 (5.4 3v) in December with about 120k on the clock. When I bought it I knew it would need plugs changed as well as some other maintenance very soon. On the first couple of tanks I got about 13-14 mpg. The truck also came with a 2 or 3 inch lift, bigger tires (295) and true dual exhaust. Around the 3rd tank I started getting a bad misfire. So I changed out the plugs and replaced the coils with some slightly upgraded options. I also cleaned my air filter (came with a k&n). Instantly my mileage with down to around 10 even on the highway. I don't drive the truck hard. I keep it below 2000 rpm aside from some on ramp merging situations. Last take littering around the town I got 8.9 mpg. My question to you all is where should I start looking for the problem. What should be changed out first and all that? I know it's a truck with a big engine and the lift and tires don't help so I'm not expecting a miracle. But 5 extra mpg on a 33 gallon tank would be a might big help.

Thanks in advance,
Nate from Brazoria county Texas

yoda13

How about changing your fuel filter? That probably needs to be done. What brand plugs did you use? These Fords sometimes don't do well on non-motorcraft replacement parts...did you over oil the filter after you cleaned it?

effects4

i'd try cleaning the MAF sensor too