MPG are horrible!? even for 5.4l!

[jlo82585]

hey y'all, first off im not complaining about fuel economy, I am very aware that I bought a v-8 on a 7 thousand pound truck. I am curious though as to why my mileage seems to be so much worse than other expeditions. I have a 2002 eddie bauer expedition with 147k miles. I just bought it so the only things I have done for it so far is change the oil and air filter and do the gotts mod to it. It needs tires and I will be getting them shortly as well as having my exhaust straight piped after the cats. I am seeing about 9 MPG in town ( about average ) and 12.5 on the highway ( well below average ). my brother usually sees 14 on the freeway and my sister claims her expedition gets between 16-17 on the freeway so does anyone have any ideas as to why mine is so much worse? the original window sticker for my truck says 16 highway and 12 in town. Are the numbers im seeing about normal or is there something I should be checking?

 

[MoHawk]

Was it ridden hard and put away wet? My 2005 gets 15 city and 22 Hwy....

 

[bedrck46]

whens the last time you changed plugs COP's etc, clean the throttle body exhaust ports What your getting highway I get around town and I haven't changed plugs yet I would expect you to do somewhat better

 

[jlo82585]

I don't think so, the engine doesn't burn a drop of oil though it leaks a few drops a day, after changing the oil and going about 500 miles the oil still looks totally clean so the rings would appear to be okay. The exterior is 100% clean ( except the typical rocker panel rust ) and the interior looks brand new. it does have an exhaust leak and the transmission needs to be serviced as the fluid is very dirty but all in all it seems to be running great. no CEL ( when I bought it the CEL was on due to the MAF sensor being unplugged ). your 05 would have the 3 valve 5.4 so you should be getting better mileage either way but for the 2v 5.4 im still way off what I should be getting supposedly. I haven't changed plugs yet, im actually dreading it after seeing where they are located but that is my next step. Should I replace coils with plugs?

 

[tonydiv]

Those mpg numbers are worse than my truck was getting with the setup you see below.

It's time to hit all the basics. Fuel, air filters. Clean mass air meter. Sea Foam the intake. Change fluids. Check air pressure in the tires. Ignition system maintenance.

Once all that is all done. It's time to check the rest of the driveline to make sure that nothing is dragging.

 

[bedrck46]

if you don't change coils at least install new boots and use dielectric grease Clean the throttle by removing it from the intake pay attention to the exhaust ports thru the TB

Also agree with above by tonydiv

 

[jlo82585]

well ill be dropping the fuel tank soon to replace the fuel level sending unit so ill change the fuel filter then too, air filter is already new as is the oil. Just got the tax return so ill get some new rubber as my current tires are worn, weathered and one has a broken belt. when I pull the TB isnt there a gasket ill have to replace? and do I just use carb cleaner to clean it out? plugs are in order as well, as for the dragging, it seems at low speeds 1-2 mph when I crank the wheel on pavement the front tires drag a bit, I was told this is normal. I can hear the T-case engage / disengage when 4lo is selected so as far as I can work out that is all functioning correctly.

 

[allanbegg]

... and the transmission needs to be serviced as the fluid is very dirty ...

Transmission slipping, perhaps?

 

[bedrck46]

you will need gaskets for the throttle body also use throttle body cleaner. Some good videos on youtube about cleaning TB's since your dropping the tank you may want to consider replacing the fuel pump as a complete unite being your mileage is up there unless you know if and when the pump was replaced.

 

[toms89]

It may be worth changing the upstream O2 sensors. (nearest the engine) These are used by the pcm to tune the engine. You can have your exhaust checked for back pressure to determine the condition of your cats.

Do you keep your tires properly inflated?? Rolling resistance can have a big impact on fuel mileage with a heavy suv. I like to keep mine on the higher side to help reduce rolling resistance but well within the range of the tires specs. Tire wear and comfort are possible disadvantages but you can monitor tread wear and alter pressure as necessary.

 

[jlo82585]

Transmission slipping, perhaps?

I don't think so, it sure doesn't feel like it and from what I have read the trans on the expedition is pretty much bullet proof but the engine seems to work pretty hard as the RPM's rarely get below 2k when im moving.

since your dropping the tank you may want to consider replacing the fuel pump as a complete unite being your mileage is up there unless you know if and when the pump was replaced.

the fuel level sending unit I bought is the complete float / pump assembly so that's in the mail and will be done as soon as i get it

It may be worth changing the upstream O2 sensors. (nearest the engine) These are used by the pcm to tune the engine. You can have your exhaust checked for back pressure to determine the condition of your cats.

Do you keep your tires properly inflated?? Rolling resistance can have a big impact on fuel mileage with a heavy suv. I like to keep mine on the higher side to help reduce rolling resistance but well within the range of the tires specs. Tire wear and comfort are possible disadvantages but you can monitor tread wear and alter pressure as necessary.

wouldn't a bad O2 sensor set off the CEL? and I thought bad cats would improve mileage as there is less restriction ( provided it blows the material out of the exhaust ) but either way im having the truck straight piped next week. As for tires, as soon as I can find a good tire that has good off / on road specs im getting them.

 

[splintrcel]

What are you using to calculate your mpg. The onboard computer doesnt really give an accurate reading. It is lies! It usually says your getting way worse on high way then you actually are.

 

[jlo82585]

the onboard computer for the fuel display is currently non-functional as my truck does not have a functioning fuel level sending unit so I have been taking the miles on the trip odometer and dividing it by the gallons I put in at each fuel stop.

 

[FordandPolaris]

Bad O2's can read bad voltage (the way they communicate their data with the comp) without setting the CEL. They are not easy to change though, I've tried a couple of times and cannot break them loose.

Bad cats usually plug up, and so they restrict flow more. Very rarely does a cat blow apart.

 

[BAD RONALD]

Bad O2's... are not easy to change... I've tried a couple of times and cannot break them loose.

I haven't used the stuff but guys swear by this penetrating oil, esp for frozen O2's.

Welcome to MouseMilk.com

 

[toms89]

Narrow band O2 sensors such as used in the expy can only read rich or lean, they cannot actually tell what the air/fuel ratio is. The pcm maintains stoich (14.64 to 1) by constantly toggling back and forth between rich and lean. This happens very quickly when the O2 sensors are new or in good condition. As they age and/or possibly get contaminated they may become slow to respond and this affects the pcm's ability to tune properly.

Catalytic converters, if contaminated (coolant, oil, ? ), run rich for too long, overheat, etc..... can become clogged. This happens progressively overtime and they become more and more restrictive to exhaust flow and may be difficult to detect until it gets to the point it causes driveability issues or sets cel.

Yes they may eventually burn up and break apart if overheated long enough, and your vehicle doesn't stop running first, but generally not till long after they restrict flow.

 

[jlo82585]

well after the gotts mods and a tune up ( oil and air filter ) i am now getting 10 MPG in town so its an improvement. I am having the truck straight piped tomorrow so that should help too, as well as new tires late next week..
I never thought about the way O2 sensors work but I also have to ask is it a common problem for the O2 sensors to go out or give bad reading without tripping the CEL? And as for cat contamination, if I was passing oil or water through the exhaust wouldn't I be having a misfire or CEL (due to the O2 sensor) on one of the cyl? Im still hoping plugs, tires, and fuel filter will correct the issue but it still has 2MPG in town to go and that's a stretch for those fixes...

 

[toms89]

The on board diagnostics with the pcm is designed to aid in diagnosis. It is by no means perfect. Only when certain parameters are met, or sensors exceed a given value will it set a cel and store the code. Does this mean it detects every issue every time and know whats wrong with your vehicle? No. I really wish it would tell me what's happening with my expy half the time but unfortunately it does not. I have had severe misfires before but as far as the pcm was concerned everything was just cherry.

Seems many put a lot of faith in the pcm as I have seen this question asked frequently. After seeing the software and experience tuning my expy I feel otherwise.

Yes if the pcm sets a cel it has detected an issue but it does not necessarily follow that no cel equals no issue.

Been over 20 years since I took logic class and can't remember the term for this but it reminds me of that class every time I see this question posted.

 

[toms89]

Found this via google:

What the Home Mechanic Needs to Know about O2 Sensors

Probably explains it better than I....

 

[FordandPolaris]

Straight piping will not help for two reasons. One is you won't keep your foot out of it, and the other is that the engine will have no back pressure and therefore low end torque will suffer. MPG's goes with that.

I would second the notion that O2's will go bad before they throw a code. My MPG's dropped off noticeably with no CEL a few years ago, and only last year did I start getting O2 sensor circuit CEL's. They are the last part of my system that needs to be replaced, so they have to be the culprit as nothing I have done has really resolved the fuel mileage issue.

Also no, if oil and water is getting into the cats, it will not cause a misfire. This stuff is way past the spark plugs. Tom has explained this to me before, and if the O2's go completely bad (through being fouled or other means), the computer has a crisis mode tuning table that it falls back on. Basically the truck still runs fine, the MPG's just suck. Instead of burning money having the muffler cut out, have the guys change the upstream O2's and be amazed as your truck gets better MPG's.