I have recently purchased a used 2005 F-150 4dr Supercrew 4x4 with a 5.4L Triton and have recorded mileage between 8.5 and 12.2 mpg. I have also noticed some drive ability issues that may lead to this issue. It likes to idle at about 600 rpm in gear and rolls backward with your foot off the brake on a mild grade. I can also feel that it idles a little rough. After reading some posts there seems to be alot of talk about fuel quality and spark plug issues. I have an extended warranty and can bring it back to the dealer but want see if someone has experienced the same issues. My wife has a 2006 Mustang GT with the 4.6L V8 and uses BP midgrade fuel and has increased her mileage to 23 mpg on the highway from 20 mpg using BP's regular grade fuel. Her gas cap and owners manual both recommend BP fuel and she has used it for almost 35k with no problems.

 

I also have a 2005 5.4 liter FX4 supercab.
Mine idles at 600rpm, was getting 11mpg until I installed the edge tuner and now I get 14mpg if I drive normally without getting into it much.
And yes, if I run cheap gas the fuel economy drops big time. some in here claim to get 18mpg and then some. But I also am running 35" tires with a 6" susp lift.

If I had to guess, sounds like your truck needs a tune up or more if your running stock tires and such.
If you go with new plugs you had better do your research, there is a link in here that has a video showing whats up with the 5.4 liter plugs if you do a search you should find it. I highly recommend watching it, some in here have been charged $1600 and up to have the plugs changed by ford dealers after they break the ceramic on the plugs.
The plugs are broke into 3 pieces and require a special tool to fix if the ceramic breaks and the grounding insert gets stuck in the head. If the tool does not work then you will have to pull the heads completely off to repair them.

Anyhow, hopes this helps you some. Its 3:40 am right now, Im sure you will get some more answers tomorrow after the sun comes up fer a bit.

 

Thanx for the info. Just got the truck 2 weeks ago and am starting to do the research. Any thoughts on exhaust systems, headers or such? Want to keep it as stock as possible but giver' a little more punch. It's my daily driver.

 

You didn't list the mileage on the truck, but if it is up over 70k, a number of things could contribute to the poor fuel mileage. Tired O2 sensors, dirty throttle body, worn plugs. All things that won't be covered under your warranty......

 

100% agree.

I wouldn't assume, unless you have reliable documentation to the contrary, that ANY of the myriad number of items that constitute comprehensive maintenance on these trucks was done. Hence, for your own peace of mind, you should have them all performed. See owner's manual or the Motorcraft Service website for intial guidelines.

 

Thanx again for the info. The mileage on the truck is 38,500. According to the dealer it has 100,000 mile plugs. I don't see any critical maintenance which needs to be performed at this time. All the talk about plugs and fuel quality lead me to believe something in this area my be the problem. Being used, I don't know the previous users maintenance habits or driving habits. I still know a few buds at the dealership that have been techs there for over 25 yrs. Maybe they can get this figured out covered under my extended warranty.

 

I only get 11 or so city in my truck its a 4x2 reg cab with the 5.4 the 15 Ford says it is supose to get must be a joke.

 

My 2005 FX4 SCrew (5.4L, 3.73) idles at 600 RPM. The roll back on a slight grade is normal. My F-150's, Expedition and Sport Trac all do it.

The 2005 FX4 was stock and still got 13-14 MPG city and at least 19 MPG highway. Gas mileage will suffer if you're heavy footed. I would probably take it to the dealer and see if you have an O2 sensor going bad.

 

If you've got a heavy foot in an urban area you're going to get bad gas mileage. Living in Denver I get between 12-14 if it's only town driving, when I go on long road trips I can get between 17-20 depending on the speeds I travel. A full fuel system cleaning and a good cleaning of the MAF and IAC would be a great start that will only cost you around $80. good luck

 

ecubcadet,

Welcome to the forum from another Illinois member. Here's something you might try. It's free too. Disconnect the negative lead from the battery for about 30 minutes. Let the computer reset itself upon reconnection. You'll have to reset your radio presets but all else will be normal. Now drive the truck like you would normally. Over time, the computer will adapt to your driving style. However, a lead foot is a lead foot. If you get on it from every stop, your mileage will suffer. Also, if you drive mostly short trips in town with a cool motor, your mileage will suffer. Once it's warmed up, it will run much better. I've noticed this with mine. I have a 2005 5.4 except it's 2WD. Try the free things first before throwing parts at a truck that is barely broken in. No telling how it was used or driven by the previous owner. The computer reset may help a bit.

DMAC

 

I get 22 in my 99=F150 5.4

 

stock my 97 f-150 4.6L got 10MPG then i added headers and a CAI im geting about 15-16 city and around 20 highway. thats on 87 and i also have new plugs. i thought if you run a diff grade of fuel you need differnt plugs and the timeing needs to be different? will my truck increase gas mileage if i use a higher grade of fuel? ive always liked Shell gas it works for me!

 

I have an 05 fx4 supercrew with 5.4l and 3.73 rear end, 16 mpg is the worst I have gotten so far, that was all around town.Havn't taken it on a trip yet to see what it gets on the highway.I try to keep the rpms under about 2500.

 

Mind sharing how you do that? All stock? I have a 1997 F150, 5.4, currently get maybe 10, although I have some work to do on it for sure.

 

I have a 2000 5.4 Lariet SuperCab 4X4 with K&N filter, Turbo muffler and 3.55 rear. I get 15 mpg running around Houston and 17.5 mpg on the road with cruise at 70. Running it with Shell 87 and Mobil 1. It has 98,000 on the clock and I am looking at changing the plugs at 100,000. I am getting paranoid about the plugs with all the problems everyone has had and hope I don't.