99 7.3 Bad fuel Mileage - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 23 (permalink) Old 02-22-2012, 03:27 PM Thread Starter
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99 7.3 Bad fuel Mileage

I need some help. I am a mechanic, but not a diesel mechanic. I bought a 99 F250 a year ago and I am not getting the fuel mileage that everyone says I should be getting. In the city, on the highway, loaded or unloaded, towing or not, I have not gotten over 14mpg.I am hearing everyone says that they are getting in the 16-20 range. I do not drive hard at all. I do have a superchip programmer on it but even at the stock setting, or the fuel saving setting, it is no better. Here is what I have done so far:
-Checked every sensor I could find for correct resistance, temperature, etc.
-Checked for exhaust leaks and restrictions up-pipes and all.
-Checked for boost leaks
-Checked the turbo for excess play
-Changed fuel and air filters
-Filled the fuel bowl with seafoam
-Ran several bottles of cleaner through the fuel system
-Checked for dragging brakes
-Checked boost pressures
-Checked fuel pressure -57psi
-Removed and cleaned exhaust back pressure valve
-No smoke in the morning when first started, if there is some it is so faint you can not see it.
- Very little black smoke when you really get on it
-Tires are 32's on stock wheels
The only thing I have not done to date is checked the injectors or injector o-rings.

I don't know what else to do. Help please.
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post #2 of 23 (permalink) Old 02-22-2012, 04:15 PM
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Re: 99 7.3 Bad fuel Mileage

How many miles on it?

Might do a compression check.

REBORN 20 Over on 3/2/11- Pics in gallery- 2000 F250, Auto, 38r, Full Force 238cc/100%, TE 17* hpop, DP F5,HI,60T,80E,120R,140A, Studs and 910's with DI PR's, JW VB in 2nd stock tranny, Walbro 392, Bellowed, In-Tank, Pre-Pump, boost fooler, and RR. Air Dog, SS cover, 6.0 TOC,4" straight piped and guages, 6637, coolant filter, 4" Lift on 33's.
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post #3 of 23 (permalink) Old 02-22-2012, 04:52 PM Thread Starter
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Re: 99 7.3 Bad fuel Mileage

170K miles. I know it is possible, but I know the original owner and the services have been kept up religiously. I will look into it, any other ideas?

'99 F250 2WD 7.3 Crewcab LB 170k miles Leveling Kit with 285/75/16 mud tires on stock wheels
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post #4 of 23 (permalink) Old 02-22-2012, 05:06 PM
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Re: 99 7.3 Bad fuel Mileage

i have same trk im getting same as u
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post #5 of 23 (permalink) Old 02-22-2012, 05:07 PM
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Re: 99 7.3 Bad fuel Mileage

sorry mines 4wd
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post #6 of 23 (permalink) Old 02-23-2012, 04:07 PM
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Re: 99 7.3 Bad fuel Mileage

When I had my 2000 psd it got around 14 to 15 empty and around 9 to 10 when pulling around 5000lb. That was with a 60hp tune from my predator tuner. I have never know a 7.3 to get 20mpg. My 6.0psd did everytime though.
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post #7 of 23 (permalink) Old 02-23-2012, 05:11 PM
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Re: 99 7.3 Bad fuel Mileage

Dieselsite boost leak detector..good tool
What size tires, how much air in each,gears all have impact.
I got 15.7 stock prob 17 on a great day now.
Best guess is 12 towing.

Bte useless meter says 19'7 now, I just use it to let me know better or worse.
Tunes throw them off.

Early 99 f350 4x4 crew cab, auto. pmt2 pcm
2001 cup holder ,T500, MAX AC ASSIST AC mod, Diy Twin tymar, TS chip, Powerslots & Hawk pads, ford AIC, ..... with big fat want to list.
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post #8 of 23 (permalink) Old 02-23-2012, 06:00 PM
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Re: 99 7.3 Bad fuel Mileage

Have you accounted for your tire size being larger than stock, which will make your speedo/odometer read low?
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post #9 of 23 (permalink) Old 02-26-2012, 04:34 PM
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Re: 99 7.3 Bad fuel Mileage

i have an 01 f350 cc,lb,drw,4wd now with the 7.3 and she gets about the same as you, and previously i had a 2000 f250 ec,lb,srw,4wd 7.3 that got the same as well, however the 97 cc,lb,srw,2wd, 7.3 that i had would get just about 20 on the highway. Tire size could account for some, changing the gears out might help you, but it can be pricey on a 4wd
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post #10 of 23 (permalink) Old 02-26-2012, 06:07 PM
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Re: 99 7.3 Bad fuel Mileage

I feel your frustration. My first 01 cclb 4x4 stock hieght got 16-19mpg. My 02 cclb 4x4 gets about 12-15 both city and highway 33" tires and 4" lift. I know the lift and tires dont help but I cant see a 5mpg improvement if it was at stock hieght. Im not calling anyone a liar but I find it real hard to believe some of the guys who claim 20+ mpg running 37's w/ big lifts. If they are, I'd love to see what they are doing different. My first 01 cclb 4x4 got way better mpg's then my current 7.3 even after I lifted it. But not 20mpg. I dont know why this is.
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