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Hey guys I'm at the end of my rope here.
I have a 06 Dually auto with 4:10 gears
I have put 35" tires on it
I have replaced the injectors
All the filters
It has 135000 miles
I recently installed efi live
My problem I still only get like 9.8 mpg that's hand calculated
I'm open to anything at this point
Oh yeah I drive it like an old man
So where or what do I do from here
I have a 06 Dually auto with 4:10 gears
I have put 35" tires on it
I have replaced the injectors
All the filters
It has 135000 miles
I recently installed efi live
My problem I still only get like 9.8 mpg that's hand calculated
I'm open to anything at this point
Oh yeah I drive it like an old man
So where or what do I do from here
1 - 20 of 76 Posts
It's actually not.
They got it as close as they could at the dealership. So at 65 I'm actually doing 68 via gps
What are u thinking
They got it as close as they could at the dealership. So at 65 I'm actually doing 68 via gps
What are u thinking
Well, my original thought was you were putting more miles on than your odometer was reading, hence the low mileage.It's actually not.
They got it as close as they could at the dealership. So at 65 I'm actually doing 68 via gps
What are u thinking
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I would guess the 4.10 gears and the large tires are costing you a couple . 4.10 gears are making the engine turn at a higher rpm when driving and the larger tires although the help fight against that a little they still have un-sprung weight and cause the engine to work harder to turn them. Also I don't know how you drive but an aggressive driving style will effect your mpg also.
Is that mileage empty or pulling something? I get 15 (hand calculated) on average city/highway driving so I wouldn't blame the tire/gears much. Granted they don't get you better mileage but with your set up you shouldn't be losing more than 1 or 2 mpg like Jim 5150 said. On my worst day pulling 18000 I'll see the mileage you're getting now. How about your air intake set up? Is it breathing good? So many factors relate to fuel mileage problems. Is your exhaust stock? If you are tuning with EFI I'm assuming you have the basic mods. Engine needs to breath if you're giving it more fuel electronically.
Actually the 4.10 should be helping some with the larger tire. Stock with 3.73 and 35 with 4.10 are almost identical overall drive ratios so you are really only being hit by the extra width. Now if the tires are mudders they will get worse mileage than an AT which gets worse mileage than a street tread.I would guess the 4.10 gears and the large tires are costing you a couple . 4.10 gears are making the engine turn at a higher rpm when driving and the larger tires although the help fight against that a little they still have un-sprung weight and cause the engine to work harder to turn them. Also I don't know how you drive but an aggressive driving style will effect your mpg also.
It's technically just the weight of the tire and the extra rolling mass that sucks a little more fuel so it depends on the type of tire you choose (6, 8, 10 ply) I love it when people blame the lifts on trucks for getting worse mileage. Like the extra height or ground clearance really makes any difference. 
Extra height does make a difference. It increases the wind resistance by allowing more air to flow under the truck which is not smooth air flow. Manufactures do a lot of work to minimize air flow under a vehicle for this reason.
Sorry but I completely disagree. The wind is hitting your axles rather your truck is lifted or stock. The little air dam on the front is not making enough difference to start taking away miles per gallon. I'm not about to drive a truck on stock tires with a lift at the cost of looking stupid to prove that opinion though.
I agree there isn't much difference but there is a difference (<0.5mpg). Believe what you want though.
Bigger difference is the rolling resistance of the tires. Mud tracks can lose 2MPG or more over a street tread.
Bigger difference is the rolling resistance of the tires. Mud tracks can lose 2MPG or more over a street tread.
<.5 I can agree with. But then again I don't lift my trucks and then worry about my the fuel mileage either. Look at my mods-obviously I have a different goal in mind. I just don't think a little more wind resistance under a 4 ton truck is gonna be significant enough to be a big factor is all.
Completely off topic but bigslacker I'd loooove to see some pics of your truck
Rotating mass (wheels and tires) and airflow under the vehicle make a significant difference. Just take a look at the latest pickups on the market. They all have huge air dams to prevent air from going underneath the truck and move it around the truck instead. Same thing with commercial trucks where mpg=profit. Many of them have super low front bumpers, side farings and trailer skirts.
The 4:10's are not helping either. Anything that bumps up rpm's at highway speeds will kill fuel econ, large tires or not.
Driving "like an old man" is in the eye of the beholder. I practice progressive shifting, never above 1500 rpm and always start in 1st. VERY slow off the line but makes a big difference driving in town. You can do the same with an auto too. Just go really light on the go pedal and watch the tach. The trans will upshift at lower rpms if it doesn't sense much engine load. Try to make it upshift as low as possible. And as you've probably heard a million times, try to keep your highway speeds under 60mph as much as practical. Cummins has a really good white paper on fuel economy. Lots of good info in there.
All that said, you've gotta clean out the cobwebs once in a while... :thumbsup:
The 4:10's are not helping either. Anything that bumps up rpm's at highway speeds will kill fuel econ, large tires or not.
Driving "like an old man" is in the eye of the beholder. I practice progressive shifting, never above 1500 rpm and always start in 1st. VERY slow off the line but makes a big difference driving in town. You can do the same with an auto too. Just go really light on the go pedal and watch the tach. The trans will upshift at lower rpms if it doesn't sense much engine load. Try to make it upshift as low as possible. And as you've probably heard a million times, try to keep your highway speeds under 60mph as much as practical. Cummins has a really good white paper on fuel economy. Lots of good info in there.
All that said, you've gotta clean out the cobwebs once in a while... :thumbsup:
Yes that's empty
At 60 I think around 1800 rpm
They are very mild all terrain tires
I also have an aftermarket air raid on it
At 60 I think around 1800 rpm
They are very mild all terrain tires
I also have an aftermarket air raid on it
I have found that my best highway mpg is at 1900 rpm ~65 mph. Going to 2000-2200 rpm at ~70 mph and the mpg falls off precipitously. I am running 285/75/17 Duragrapplers.
What's you rpm at highway cruising speed? At what point during your mods did you start getting bad mpg?
I would also consider looking into your EFI tuning, maybe let your tuner know what's happening and see if they can give you some different tunes to test.
What's you rpm at highway cruising speed? At what point during your mods did you start getting bad mpg?
I would also consider looking into your EFI tuning, maybe let your tuner know what's happening and see if they can give you some different tunes to test.
Interesting.... I have read on here somewhere that shifting below ~1500 in higher gears puts more wear and tear on the clutch. Any truth to that?Driving "like an old man" is in the eye of the beholder. I practice progressive shifting, never above 1500 rpm and always start in 1st. VERY slow off the line but makes a big difference driving in town. You can do the same with an auto too. Just go really light on the go pedal and watch the tach. The trans will upshift at lower rpms if it doesn't sense much engine load. Try to make it upshift as low as possible. And as you've probably heard a million times, try to keep your highway speeds under 60mph as much as practical. Cummins has a really good white paper on fuel economy. Lots of good info in there.
Well your mpg will be off cause speedo as well. Your trip will register less miles than actually traveled. So when you divide in your gallons you filled up with itll be lower than it actually is.
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You can remedy this by using a GPS instead of your odometer. That's what I use. Can't get more accurate than that. Maybe you should check and see what you are actually getting.
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