2002 7.3 mpg drop
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5th Wheeling
Joined: Sep 2007
Posts: 45
Likes: 3
2002 7.3 mpg drop
I bought a 2002 f250 diesel automatic last summer. 4 door short bed with 133 k miles. Upto to 149k now. When I got the truck, the lie o meter and my own calculations said I was getting about 19.5 on faster highway driving (75 mph +) and could get around 21 if I drove 65. Mixed driving was probably 15. Now I can't get above about 16 on interstate driving, probably 13.5 mixed driving. It has a 4 inch turbo back straight pipe and the ford AIS intake. I cleaned the exhaust back pressure sensor and tube months ago and it didn't help. I have noticed that my fuel gauge drops very quickly from full, then when it gets to 1/2 it appears to stay there much longer. Could an inaccurate fuel gauge be the culprit or something else?
Senior User
Joined: Jul 2015
Posts: 124
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Have you done the Hutch and Harpoon mods? My X stays on F for over 100 miles before it drops, and we routinely get 20ish on the hwy. Last trip to OK we went 960 miles on the tank, but I rode on E for a bit just pushing it to see how far it would stretch. Put a dab over 43 gallons in. This was immediately after doing the hutch and harpoon, and I think it was in part due to eliminating the clogged fuel screens from inside the tank. Before I'd be lucky to go 800 miles.
It's a Van Gogh
Joined: Feb 2010
Posts: 7,802
Likes: 1,333
From: Elk Grove, CA
149k. 
If you hand calculate the MPGs the fuel gauge has nothing to do with it.
My first guess was the exhaust back pressure sensor, but you already got after that one.
Second guess is winter fuel. My mileage drops about 1 mpg when the winter fuel comes out. Summer I see 15 and winter 14, mixed empty driving, less than 20% WOT.
Third guess is neighbor siphoning fuel.
X2, one of the best mods you can do is the Hutch and Harpoon. Good primer on it at Guzzle's page. I did a version of that and going like 90 miles before the needle moves off of full is fun! But the short bed tank is smaller than the long bed so most I ever get in there is 35 gallons.
If you hand calculate the MPGs the fuel gauge has nothing to do with it.
My first guess was the exhaust back pressure sensor, but you already got after that one.
Second guess is winter fuel. My mileage drops about 1 mpg when the winter fuel comes out. Summer I see 15 and winter 14, mixed empty driving, less than 20% WOT.
Third guess is neighbor siphoning fuel.
X2, one of the best mods you can do is the Hutch and Harpoon. Good primer on it at Guzzle's page. I did a version of that and going like 90 miles before the needle moves off of full is fun! But the short bed tank is smaller than the long bed so most I ever get in there is 35 gallons.
Cross-Country
Joined: Aug 2007
Posts: 72
Likes: 4
From: Arendal, Norway
When I bought my X it used like 18l to 100km and went down to 11l /100km (@55) due to a faulty ICP sensor. Hook up and check out your sensors, if one or more are not working correctly it will still perform - but use more fuel. To me a rise in fuel consumption is a worning sign that need to be addressed. Good luck.
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
I expect to see a 10-15% drop in winter driving where the climate is cold, but here's the kicker: My P'us drops the same amount in the winter, and it doesn't use winter mix diesel. Cold weather burns more fuel with denser air and longer warm-up times, plus we load up the engine with the A/C compressor any time we have it on the vents or defrost. I'm not saying the winter mix thing is a myth, I'm saying it's in cahoots with a lot of other factors to attack our mileage.
That being said, something else is afoot with such a large drop in economy. Two things come to mind:
Either way, we're in the tall weeds without some sensor readings while driving. Apps are getting so inexpensive and almost everybody has portable electronics, I offer up a suggestion that you acquire something like this to figure out what's going on in there.
That being said, something else is afoot with such a large drop in economy. Two things come to mind:
- I have had limited success with cleaning the EBP sensor, and I ultimately had to replace it when it failed the KOEO test.
- Air leaks in or out kill power and economy.
Either way, we're in the tall weeds without some sensor readings while driving. Apps are getting so inexpensive and almost everybody has portable electronics, I offer up a suggestion that you acquire something like this to figure out what's going on in there.
Junior User
Joined: Apr 2012
Posts: 60
Likes: 0
From: Romeoville
I bought a 2002 f250 diesel automatic last summer. 4 door short bed with 133 k miles. Upto to 149k now. When I got the truck, the lie o meter and my own calculations said I was getting about 19.5 on faster highway driving (75 mph +) and could get around 21 if I drove 65. Mixed driving was probably 15. Now I can't get above about 16 on interstate driving, probably 13.5 mixed driving. It has a 4 inch turbo back straight pipe and the ford AIS intake. I cleaned the exhaust back pressure sensor and tube months ago and it didn't help. I have noticed that my fuel gauge drops very quickly from full, then when it gets to 1/2 it appears to stay there much longer. Could an inaccurate fuel gauge be the culprit or something else?
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Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
I have the same exact truck with a 3:73 gear. Extended Cab less weight than 4 door. 6 1/2" Lift. 35" Tires SCT Tuner, MBRP, K&N Air. When babying it 16.5 at best!!!! That is 64 miles an hour and lower on rural or highway roads. 13.5 around town maybe 14.5. I have never in my life heard of 19.5 with these trucks Never!
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Senior User
Joined: Jul 2015
Posts: 124
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That 6.5" lift probably isn't doing your mileage any favors, but I don't think 18+ on the highway is out of the question even on 35s. I frequently get a smidge over 20 mpg in my X on 285's and properly calibrated speedometer (had calculated - my lieometer hasn't worked in years).
Posting Guru
Joined: May 2013
Posts: 1,199
Likes: 2
From: Oklahoma
I got my best EX mileage ever over the weekend, 17.1 on Friday. I'm running the '04 18" wheels with a 3" lift. The truck averages 15.5 on the highway up from 11 when I got it. I'd love to ride along with someone getting 18+ out of an Excursion. It's my goal...
Veteran/Sheepdog
Joined: Feb 2012
Posts: 6,047
Likes: 110
From: Western AR
Jess, you gotta drive 62-64 and have pretty flat terrain for your trip to get the good numbers. 
I don't know about the wheel size factor, but I am running stock rims/tire sizes. I am not lifted, and that is not going to help your fuel mileage any since you are. Putting the big-*** ranch hand on the front of my truck is ensuring I never see those numbers again, either.
I don't know about the wheel size factor, but I am running stock rims/tire sizes. I am not lifted, and that is not going to help your fuel mileage any since you are. Putting the big-*** ranch hand on the front of my truck is ensuring I never see those numbers again, either.
