FUEL MILEAGE PROBLEMS! - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 14 (permalink) Old 03-11-2011, 08:48 PM Thread Starter
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FUEL MILEAGE PROBLEMS!

I've been running the Spartan 250 tune for 18,000 miles.

All of the following mileage numbers are hand calculated.

Based on my particular in-town driving habits (which are very consistent day-to-day), my mileage was always 11 to 11.5 mpg, starting from the time I did the tune and delete (600 miles) to 14,000 miles.

At 14,000 miles my mileage began to increase for a few tanks of fuel, then leveled off at 12.5 mpg. I was very happy, especially because it was during the winter months and the fuel was probably winter-blend!

At 16,500 miles my mileage began dropping back to the 11 mpg range. I loaded the 210 tow-tune for a tank, just to see what it would do and only got 9 mpg. Loaded the 250 again and am still seeing only 11 to 11.5 mpg.

Where is my extra 1 to 1.5 mpg!!!!!!!!!!!

Oil and filter changed every 3,000 miles. The last fuel filter(s) change was at 15,000 miles, tire pressure is set at 65 psi (check it every fill-up) and my "Green" filter looks as good as the day I dropped it in.

Any thoughts or ideas?
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post #2 of 14 (permalink) Old 03-12-2011, 03:34 AM
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wow i do not know what to say. you have 4.88 gears ?
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post #3 of 14 (permalink) Old 03-12-2011, 12:11 PM Thread Starter
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wow i do not know what to say. you have 4.88 gears ?
3.55 gears

All driving is "in-town" stop & go traffic.
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post #4 of 14 (permalink) Old 03-12-2011, 01:57 PM
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Originally Posted by Truckmaniac View Post
3.55 gears

All driving is "in-town" stop & go traffic.
I hate to say it but our Honda Minivan gets 11-13 around town, maybe this is good for a 4 ton vehicle. I am at 22.5 MPG mixed with the Spartan 275 and S&B CAI. 3.73. gears CC SB 4x4. I was at 18 with just the CAI and 16.6 before anything was done.

08 Job 2 Lariat CC SB 3.73 6.4
4" custom (i.e. made from parts from here and there) DP back SS exhaust
S&B Oiled CAI
Spartan Tuned (275)
Powerstroke 67 DPF/DOC delete
Recon Smoked Cab Lights
Dual Headrest DVD/Monitors
Rhino Liner
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post #5 of 14 (permalink) Old 03-12-2011, 02:46 PM
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Originally Posted by Greenshield View Post
I hate to say it but our Honda Minivan gets 11-13 around town, maybe this is good for a 4 ton vehicle. I am at 22.5 MPG mixed with the Spartan 275 and S&B CAI. 3.73. gears CC SB 4x4. I was at 18 with just the CAI and 16.6 before anything was done.
Is that calculated by hand? 22.5 seem pretty high especially with 3.73. I have the same gears and the best I have seen when my truck was stock height was 15.7 after tune hand calculated. 11.8 was stock MPG hand calculated.
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post #6 of 14 (permalink) Old 03-12-2011, 08:15 PM Thread Starter
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Is that calculated by hand? 22.5 seem pretty high especially with 3.73. I have the same gears and the best I have seen when my truck was stock height was 15.7 after tune hand calculated. 11.8 was stock MPG hand calculated.
Thanks for asking the question for me.

There have not been any substantiated cases of the 6.4 getting this kind of mileage if you are hand calculating the mileage.

The higher the tune, the more the truck's computer lies.

In-town, my truck's computer shows 15 mpg when I'm actually getting 11. I've seen as high as 23.9 on the highway using the mileage computer. Stop, fill-up, hand calculate and get used to disappointment when it is really 17 or 18. This subject has been on this and all the other Forums.

I'm looking for an objective opinion as to why my truck's mileage has changed so much.
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post #7 of 14 (permalink) Old 03-12-2011, 11:45 PM
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Originally Posted by Truckmaniac View Post
Thanks for asking the question for me.

There have not been any substantiated cases of the 6.4 getting this kind of mileage if you are hand calculating the mileage.

The higher the tune, the more the truck's computer lies.

In-town, my truck's computer shows 15 mpg when I'm actually getting 11. I've seen as high as 23.9 on the highway using the mileage computer. Stop, fill-up, hand calculate and get used to disappointment when it is really 17 or 18. This subject has been on this and all the other Forums.

I'm looking for an objective opinion as to why my truck's mileage has changed so much.
I just filled up to the same level as before. I have gone 53 miles and the fuel level reading is at 96.6 %. The gauge is still well on the "full" white mark. 65 mph on flat land with 5, 2 adults and three children. If I keep this rate up I will be at over 600 miles for the tank which is over 20 MPG, not unusual at all. I was at 16.6 with winter fuel and no mods. All hand calculated as My fuel is money at tax time. I went to 18 and a little after the CAI install. This will be the first full tank with the AMsoil Diesel Concentrate and cetane boost as well as all 275 tune. I suppose the only way to show is to film the entire tank and gauge being used. Has anyone done this yet? I have only had 11 miles to the gallon or slightly worse while towing my 33' rockwood trailer with 5 people, two dogs, and a half cord of wood I range from 9.5 to 11 depending on weather, terrain, and my throttle discipline. If that is your mileage around town you have a problem with your truck especially with 15.7 on highway. That is bad stock let alone tuned. My computer has been pretty close, under if anything else thus far. My fuel gauge, Spartan displays and trip odometer are the tools I use.

My truck would be gone if I only got 15.7 and 11.5 respectively, or repaired. Please do not dispute my findings based on your experiences. I drive well, perhaps you do not, I maintain my vehicle, perhaps you do not. I have to espouse those that can suddenly recall their vehicles fuel mileage from a while ago before they were modded. I know of some that modify tires, ride height etcetera, and are mad that their mods do not work out too well once they tune it( having expected to get some MPGS back) Some (one in particular) raised their truck, put larger tires and put on some bumpers and saw they were getting 8 MPG. They tuned it saw a small jump to 11 or 12 and then ranted online because they were thousands in the whole and stuck. If accusing me, or others (indirectly) of not knowing how to calculate mileage or of BS makes you feel better, great do it. I for one, am proud of my mods, can now afford to camp this season, and love the look of black smoke out the tail pipe.


Dirtymec asked if you had 4.88 gears for a reason. Think about that.

08 Job 2 Lariat CC SB 3.73 6.4
4" custom (i.e. made from parts from here and there) DP back SS exhaust
S&B Oiled CAI
Spartan Tuned (275)
Powerstroke 67 DPF/DOC delete
Recon Smoked Cab Lights
Dual Headrest DVD/Monitors
Rhino Liner

Last edited by Greenshield; 03-13-2011 at 12:04 AM. Reason: 5, 2 adults and 3 children
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post #8 of 14 (permalink) Old 03-12-2011, 11:47 PM
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Originally Posted by Truckmaniac View Post
Thanks for asking the question for me.

There have not been any substantiated cases of the 6.4 getting this kind of mileage if you are hand calculating the mileage.

The higher the tune, the more the truck's computer lies.

In-town, my truck's computer shows 15 mpg when I'm actually getting 11. I've seen as high as 23.9 on the highway using the mileage computer. Stop, fill-up, hand calculate and get used to disappointment when it is really 17 or 18. This subject has been on this and all the other Forums.

I'm looking for an objective opinion as to why my truck's mileage has changed so much.
I am not sure why your has changed so much. Mine is pretty consistant at every fill up. I get about 13-14 with the 6"lift and 37"tires. I logged every fill up for over a year on my iPhone so each tank was hand calculated
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post #9 of 14 (permalink) Old 03-12-2011, 11:50 PM
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Originally Posted by NathanScott View Post
I am not sure why your has changed so much. Mine is pretty consistant at every fill up. I get about 13-14 with the 6"lift and 37"tires. I logged every fill up for over a year on my iPhone so each tank was hand calculated
Tuned truck too? If so when?

08 Job 2 Lariat CC SB 3.73 6.4
4" custom (i.e. made from parts from here and there) DP back SS exhaust
S&B Oiled CAI
Spartan Tuned (275)
Powerstroke 67 DPF/DOC delete
Recon Smoked Cab Lights
Dual Headrest DVD/Monitors
Rhino Liner
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post #10 of 14 (permalink) Old 03-13-2011, 12:04 AM
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Tuned truck too? If so when?
Yes. Tuned Dec 2009
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