There are a ton of factors and reasons that can cause your Ex to have such low MPG.
Tell us about your Excursion. 4x4? Lift? Size wheels? Odometer? Mods? Maintenance? Last time you checked your brakes?
Stewart
__________________ The Brotherhood of FTE <~click the link 1999 F150 Lightning: WMS built block, 6lb lower, Monsterbox, Truetrac, CF driveshaft 2002 PSD F250 SC 4x2: 38R, AC codes, MBRP 4", AFE, JWVB, Riffraff HPX, CCV, and boots, ITP OBA, Live Tuned by Jody 2000 PSD Excursion 4x4: John Wood 4R100, F5, MBRP 4", AFE, BDP 1.0, ITP OBA and Pre-Pump mod, V & B code springs, Hellwig rear sway
Ok, 2001 Limited, goldish green and tan, 150k miles, (had much better mileage at about 50k) 4x4, 285 tires, same size since I got it, Tacoma WA. K$N w Hypertech programming, (getting rid of the K&N TOMORROW!!!).
I don't change oil, I just add more.
Leaks off the top end about a quart every 1000 miles
Why would brakes have anything to do with it? I would think the less effective the brakes are the better the mileage would be....
No magic bullet???? like a bad O2 sensor or something????
Changing your oil on these engines is imperative! The injectors are cycled using the engine oil through the High Pressure Oil Pump which is located on the top of the engine, which may explain the leak you have. It is a well known cause of injector problems on these trucks.
If you haven't caused damage to your injectors already, I'd be surprised, but start with changing your oil and filter immediately and adding a detergent type cleaner like Seafoam. Then after running only a short while, drain and refill and changed filter again. To possibly save yourself changing the injectors out, I would so the Seafoam treatment a couple of times. There is a possiblity that you'll be looking at replacing your injectors anyway but hopefully you can catch it before it's too late.
You should not go more than 6,000 miles between oil changes. Also, make sure you use a quality oil, like Rotella T 15W40 or a synthetic equivelent.
Brakes have everything to do with mileage if they are rubbing slightly, because than there will be friction constantly. I am not too familiar with Hypertech programmers, but I would ditch it and get a DP tuner if you really need more power than stock.
__________________
Brian
1999 Ford Expy 5.4L
Pioneer 4-way speakers, Ignition Ding turned off, Rubberized undercoating in process
Seafoam is a solvent and while it ok to use all over a gas motor, the high pressure oil system on these trucks does not like Seafoam. Sure it'll clean out all the gunk in the oil system, but unlike a gas engine the solvent stays in the system even after the oil change and has some adverse effects. I once ran Seafoam through my oil just before I changed it and my truck did not like it at all. In other words, it destroys the lubricating qualities of oil.
I know I read somewhere that it was adviseable to use either Hot Shot Secret or 2 bottles of Prolong oil additive if you're looking to clean things up on the oil side of the hp oil system.
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FTE Excursion Forum Mod Death Row Inmate #21
2001 X PSD Limited
6637 Filter
203* Thermo
SCT X-Cal2
4 in. MBRP
AT 4040
HPX
Sonnax/Tricum Kit
'04 TT Mirrors
6' PROcomp lift
35' BFGs
Bosch HIDs
4.10 Gears
WW
Walbro GSL392
I'm no mechanic, but to see a thread that starts out with need better MPG and my truck had better mpg at 50k, then one of the next lines is (I don't change oil, just keep adding it as it has a leak)
OMG are you kidding me - do you think maybe your lack of basic maintenance may have finally caught up with you a bit?
these engines are great, but you do have to take care of them.
Mine has recently started with the damn leak at the top of the motor and we are checking that out tomorrow, so I was glad to see something posted about that, thanks for that tidbit of info.
My mechanic is not sure if it is the O-rings on some lines that are on the pump or some other thing that was up there, like a sending unit or sensor (I can't remeber what he said last week) but we are cleaning it up again and then putting a small camera down there to check which is leaking and fix it.
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Jamie
Boca Raton FL
03 Excursion EB PSD 4x4
05 SRT10 Silver Q/C, 04 Mini Cooper S
88 Stang LX - drag car, 87 Stang GT Vert
Thanx for the correction Toredor... I did not realize Seafoam was not diesel friendly as I have never had to use it. I just know he needs to clean his oil system, especially in and around the injectors and pump.
OMG! threads like this crack me up... without getting in trouble with the mods for name calling I will just say the OP should probably not open the hood of his vehicle. Just and take it to the dealer at specified intervals for stated services.... your engine takes about 16 qts of oil per change and the oil filter has a bypass valve if it gets blocked up and just lets the dirty oil keep running through your engine. all the byproducts of combustion along with all the wear metals have as others stated have probably ruined your injectors and most other components.... adding 1 quart at a time does not do the same as an oil change and would still take 16K miles to change the contents of the oil... which doesnt happen cuz the newest quart is leaking/burning off at the same time as the older oil.... The filter doesn't change itself..... start with getting an oil analysis to see if the engine is already toast...
To the OP's credit, at least you got the balls to be honest... thus much easier for us to help identify the source of the problem...... now give yourself a good
"I don't change oil, I just add more." I gotta add that as a signature line...
__________________ DJ
ASE Master Auto Technician.
2001 Excursion 4x4 7.3, 4" lift & exhaust,ISSpro gauges
PHP Phoneix/Minotaur Chip, Transgo, DIY 6637 Mod, BD 200A alternator
2000 International 4700 T444E Project Truck
Why do you come on here looking for advice if you're not going to be honest?....
I didn't respond to your post because I have nothing better to do but was trying to help, or so I thought, someone that needed some advice to help save his truck.
People on this forum are unbelievably generous when it comes to stepping up and helping out with advice for those that need it, so don't jerk them around and ruin it for the rest of us!
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and take it to the dealer at specified intervals for stated services.... your engine takes about 16 qts of oil per change and the oil filter has a bypass valve if it gets blocked up and just lets the dirty oil keep running through your engine. all the byproducts of combustion along with all the wear metals have as others stated have probably ruined your injectors and most other components.... adding 1 quart at a time does not do the same as an oil change and would still take 16K miles to change the contents of the oil... which doesnt happen cuz the newest quart is leaking/burning off at the same time as the older oil.... The filter doesn't change itself..... start with getting an oil analysis to see if the engine is already toast... 
Why do you come on here looking for advice if you're not going to be honest?.... 
