Bad fuel mileage

[1955moose]

Ok guys and girls, I know you guys have run into this one. I bought my expedition about 1 month ago, it runs fair not strong. It only has 65k miles. Problem is mileage is horrible. I get less than 9mpg. Even straight line highway is only about 12mpg. I know it's a 4x4 and everything I read said 11mpg. What do you think? Idles smooth most of time. Slight roughness ocasionaly. No check engine light, brand new air filter, just passed smog.

 

[thenaaks]

What speed on the hwy? Every mph over 60 will eat away at the mpgs. If you've got a heavy right foot accelerating, 9mpg is not unheard of. Also, empty out your truck of excess weight and air up your tires.

 

[thenaaks]

Also, you didn't mention what year, engine, or other vehicle specifics (tires, lift kit, etc). That info is key.

 

[98EXPnSRQ]

I would check the brakes to see if they are dragging.

 

[1955moose]

Motor is a 5.4. I have 20 inch wheels with Nankang street tires. I have pressure at max 50 psi. Brakes don't seem to be dragging. I drive like a Grandpa. I hear all you other guys getting 11-16 mpg. My book said 11, I'd be happy with that. Sunday a mechanic friend is bringing his scanner. We'll check for dtc codes. Maybe one of the sensors is bad, don't know at this point. Thanks guys.

 

[jlo82585]

my 02 gets about 10 mpg in town and 13-15 on the highway. I do suspect on mine that the exhaust leak is causing the EGR to put too much exhaust in my system and killing my MPG and mid range power though as my brothers 01 E.B. gets about 11-12 in town and has better power even though we have almost identical miles (mine has 152k and his has 154k) and nearly identical interiors (mine has capt. seats in back and VCR player his does not) on it. the 20" though are probably your main issue.

 

[1955moose]

So having 20 inch street wheels and tires hurts mileage? Does removing the roof racks help? Also what about one of the roof wind deflectors I've seen. They work for big semi trucks. Do they help with one of the expeditions.

 

[1955moose]

Anybody out there, I need help. Usually I'm the one responding to problems but I need help. My 2000 expedition 4x4 5.4 engine gets horrific mileage. I drive like a grandpa and get between 8.2 to 9.2 miles per gallon. No dtc codes, engine runs smooth and decent power. Their is a loss of power on hills but still drivable . Mileage is 74,000. I'm running 285/50/r20 street tires. Air filter, fuel filter, o2 sensors have been changed with motorcraft parts. I'm hesitating changing plugs because of thread issue. Besides 100k plugs the norm for life of them. The weird thing is the longer I drive the mileage gets lower and lower. Will a clogged catalytic convertor cause this? The wheels and tires are close to oem for ride height and dimensions. Can't get rid of SUV at this time so any body got ideas. I'm running out.


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[IMINYOURCHAIR]

your wheels shouldn't be a problem **unless** the overall diameter is taller than the oem. you will see mpg drop as you get bigger. do a basic check of the exhaust and look for vacuum leaks and cel codes.

my expy with 3.31 rear and factory wheels/tires is getting me 18.5 average to work at 45 to 70mph and 45 miles

 

[01yellerCobra]

Change your plugs. I bet they're toast. Manufacturers talk about 100k mile service interval, but I've never seen a set actually last that long. The first gens don't have the stuck plug issues. That didn't start until the 3V's went in. Which I think was 05.

 

[jlo82585]

well depending on location that mpg isnt that far off from mine. Im in Iowa so in the summer I get around 10 in town and 13 on the highway, if I roll up my windows and use my AC i get almost 16 on the highway. winter is a different story.. im lucky to get 8mpg..

 

[98EXPnSRQ]

I have a Scan Gauge E that plugs into the OBDII port and tells me my instantaneous fuel mileage and average for the trip. It's pricey but it works well. It also can display water temp, alternator voltage, etc. and it reads and clears check engine trouble codes.

 

[DF5.4]

I would start with the plugs. If they are the factory ones you have no idea what condition they are in or if they are even gapped properly any more. Take your time doing them. they are not the ones that break but i think you have the heads with a couple of threads holding them in. When you put the new ones in use a torque wrench. They only go in snug. The spec I found is 10 ft-lbs (Ford 5.4L-330ci-V8 Torque Specifications - TorkSpec - Knowledge for the Motorhead) Here's another how to 4.6L & 5.4L F150 Spark Plug Replacement Guide Give youself plenty of time to do it.

 

[Flexpedition]

What RPMs are you seeing at highway speed? Can you feel the truck shift into overdrive, or can you feel overdrive go away when deactivated?

 

[1955moose]

My SUV definitely goes into overdrive.


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[1955moose]

The thread issue is what scares me. I've probably changed over 5,000 spark plugs over my life, but this one has got me the heebie jeebies. I used to be a motorcycle mechanic as well as a car tech. You guys are right about the plugs. I appreciate all the feedback, Moose.


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[BAD RONALD]

I wouldn't do another plug change on one of these engines again without this tool:

Gear Wrench 5/8" x 6" Magnetic Swivel Spark Plug Socket 80546: Advance Auto Parts

I understand that a spark plug change is a bit easier on a 4.6l but still don't get what all the internet ******** over the job is about. Maybe because it's more time consuming than it should be.

Do yourself a favor and dig into the changeout.

 

[z168]

With all the info presented I would start with the spark plug and air filter. Also do a seafoam flush before your next oil change

 

[IMINYOURCHAIR]

I understand that a spark plug change is a bit easier on a 4.6l but still don't get what all the internet ******** over the job is about. Maybe because it's more time consuming than it should be.

Do yourself a favor and dig into the changeout.

me either, do it right and have a method to it and all it is going to do is maybe make your back a little sore from bending. drain coolant and remove heater core hoses then pull the pugs back to front 4-8-3-7-2-6-1-5 so if you're going to mess up you do it early and you get the hard to reach first. don't be afraid to have to remove some things to get better access to it. it takes a bit but my rookie self had no problem getting it all out and done twice because I used autolite plugs (pos), and, to add to the danger level, at the time I was unaware of the five threads holding them in being weak. lucky for me I know to only run the plugs in snug.

good luck OP and keep us posted on how those plugs look

 

[1955moose]

I still am not sold spark plugs are the problem. It runs great on all but grades. But if all of you concur, well I may have to pull them. What the hell suspension problems and other crap kinda tell md my past seller may have'd fibbed about mileage. Thanks guys and girls, for your input on my problem! Moose.


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