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
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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?