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Fuel mileage question.

3899 Views 36 Replies 7 Participants Last post by  Thatrooper515
Hey guys, I'm curious about my poor fuel mileage, and if I have some underlying problem causing it or if it's just normal.
2008 f350 srw. Guessing it's geared 4:10? Straight piped. Egr completely deleted. Sct x4 tuner with custom tunes from a local shop. They said the race tune would give the best results but I usually run the tow tune since I'm pulling daily. Running 315/70-r17 all terrains with a leveling kit.
If I baby it in the race tune no trailer I get 12-13mpg, pulling in a tow tune or being a little more aggressive with the gas pedal in the race tune I get about 10-11.
Is this normal? I figured a programmed and deleted diesel should get at least 15. Poor injectors or something? New to diesels so I'm very ignorant here. Would appreciate any input.
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Was it the front or rear brakes? My front rotors get very warm compared to rear, what if I have a limited slip how could I check those? I have a 2008 6.4 deleted and tuned with Spartan tunes gets 10.5- 11.5 city very consistently and 11.5-12.5 highway. I have 6 inch lift 35 inch tires and 410 gears been gettin real tired of 10 mpg would love 15 any more recommendations? I cleaned the mat sensor it was pretty dirty but don't think I got much out of it..I run synthetic oil and boost usually seems high! Even with my foot out of the throttle I've differnt driving patterns without much success maybe 1 mpg except freeway I usually set the cruise at about 75 -78
My stats are oe and they are almost always 190-194 I thought I read somewhere that is what it's suppose to be at, but I would def move up to 205 if it got better mpg.. And just clean with brake or starter fluid om the ebps?
But where's the info to back it?
And the higher temp helps gas mileage?
So if my normal temps are 190-192 would it be worth a new t stat mpg wise? Would new injectors or a new turbo make any difference in mpg? I don't understand how one truck can get 18-20 mpg and another can get 10-12 I would love to understand what huge differences make up this 40-50 percent change in efficiency
And here is another question, would i be Better off running 37 inch tires or 35s? I would think 37s would bring my rpms down and effectively bring my 4.10 gears closer to 3.73s I'll have to check the calipers for resistance if there is just grease them or I should replace the pins or the whole assembly? And again how do I check the rear tires with a limited slip diff pull the axle shaft out I guess? I just tried switching back to the stock tune with dpf delete if the lie o meter is acuracte without the tune than I should be at 13 city and haven't driven on the highway yet so that would already be an improvement.. Last tank consisting of 3/4 tank at 75-78mph and last quarter city calculated to be 11.9 347 Miles (times1.12 for actual mileage with 35s equals 388 with 32.6 gal of fuel not very good for mostly highway driving...
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Btw I'm in Texas so only a few thousand feet above sea level and higher cerane rating assuming the info stated earlier was correct about tx and ca I'll check the brakes today and get back
Well the front right seems like it maybe frozen it doesn't roll after I'm done rolling it. It stops pretty fast and the front left rolls for a second not flvery long tho and still not sure how I will check the back.
And the stock size is suppose to be 245 75 17 which is 31.5 and I cruelty have 35s so 31.5x3.14 equals 98.9 and 35 x3.14 equals 109.9 109.9/98.9 equals 1.11 so I need to multiply my mileage by 1.11 and I figured the lie ometer thing out but it could say I'm getting 15 and I'll be getting 10.5 or it can say 18 and I'm getting 11.5 but I can never seem to get over 18...
And yes you are right that there is more weight but weight will only factor in city if you never stop the only thing that will affect mpg will be resistance be it rolling or wind so yes I may get a touch more resistance from 1 inch of tire but the weight will not negatively affect my mpg on the freeway so it will hopefully act at 373 gears instead of 390 ish with my tires now
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Never thought of getting the new tunes for that, are you speaking from experience or what you've heard? And I have 35x12.5 20s I never said 315 70 17s even if they were 34.7 how either way you look at it 9% vs 11 I it's even lower than we expected! ? lol And that 3 percent difference only accounts for 1/3 mile per gallon when I'm getting 11 that's a very small percentage. You would be right about the added wind resistance. I mean yes I understand I'm not going to get 20 mpg but I would hope to get better than a stock 6.4 when mine is deleted and tuned. Stock I've heard of 15-16 if it's not going through regen all the time and with regen it's still getting 10 -11 same as mine except I'm not dumping fuel out like a stock truck I would just love to figure out what's accounts for the other % lost in fuel economy does anyone else's front Huns get too hot to touch with highway driving I'm wondering if that could be a cause. They were pretty hot last long trip I took but maybe it's normal brake heat? Thanks for the ideas tho guys keep el coming!
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