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Lousy mileage, What can be done to improve it?

2K views 28 replies 10 participants last post by  steve05ram360 
#1 ·
I have lousy 373 gears and do not tow much of anything.
What can I do to improve MPG?
I have FASS and Sporty on setting 1.
Are there better highway gears to install?
An overdrive?
Would like to get RPM's at 80 from 2200 down to 1800-1900.
Thanks
 
#2 ·
I've looked at the same thing. Some options are free-spin hubs, different gearing in the axles and add-on, 2-speed gear boxes. All are rather expensive, so if there's not some other great benefit, I just pay the pump. The pay back for something that costs $1500 of more and increases MPG by 1 or 2 is just too long. I got the truck for towing power and 4-wheel drive, and it excels at that, so I don't worry a lot about mileage.

BTW, this gets almost double the mileage my GMC V-8 got when towing my travel trailer.
 
#3 ·
OP, lousy is a relative statement. What exactly is lousy to you? I have the 3.73 also and get a solid 20mpg on the open road. 14mpg towing an R-Pod and about 14/15mpg combined in town driving. The best solution to better mileage is slow take offs and a slow throttle right foot.
 
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#4 ·
12-13 combined mostly city, 16 h ighway in Texas at 75. Drive like a granpa, basically slow up and let off gas early and coast to stops a lot.
Do not know if cat was ever changed or if original?
 
#5 ·
A tuner that will allow timing advance, 33-34" tires but keep them around 11" wide with AT tread and don't get the light duty ones, keep the speed around 70-72. That should add 2-3 mpg on the road and maybe a couple in town if you are easy on the throttle.

Your mileage figures are pretty normal for a 8k truck hampered by emissions tuning. If you want more than the above can give it will take custom tuning and some hard part changes, there is only so much that can be done with OE parts.
 
#6 ·
Where do you do most of your driving, Highway or city? You could do a gear change to get there but your going to suffer more around town. Larger tires would offset that as well but again that will kill your in town mileage.

The truth is, there is no magic pill for mpg. I have a Smarty tuner and have tried every combo of tunes under the sun and have seen little to no increase in mpg.
You could literally throw thousands of dollars at it to save .5 mpg. The pay off just isn't there.

.
 
#7 ·
Not much emissions equipment on an '04. Reason the oil runs so much cleaner, no in cylinder EGR with 3rd injection event. the carbon burning CAT does not effect mpg as long as it is not plugged, take it out and tow heavy, burns the carbon out of it.

Use an injector cleaner in it, may be slow sealing leaker dripping nozzles from dirt/carbon buildup. Get a gallon of Fleetguard Cummins Fuel System cleaner and double dose the fuel tank at least 2 tanks. Rings may be seized up by carbon buildup, decreases MPG.

Keep the rpms under 1900 on shifts and running empty on freeway, an '04 should crack 20 mpg flat ground. Unless the TC LU is not functioning correctly, brake/s dragging pad, or nozzle leaking that cleaner won't free up to seal between injection events. The 03 04 OEM injectors do have a higher wear rate. Pull an oil sample and send in to oil analysis lab for diesel contamination in fuel from leaker nozzle. Any higher than 2%, new injector time

Pull and have injector lab tested as last resort

'06s are lucky to crack 18 mpg on a good day with top mpg driver.

Don't look at the stupid boy toy "gauge" on the overhead.
 
#8 ·
Smarty says to crank the smarty up for the best mpg.
Most on here will tell you to slow the h^ll down. You are pushing a 8K brick down the road. Try a tank at 55-60mph. I bet you will be surprised.
Some tires just aren't made for high mpg. What rubber are you running now? Don't go wide. Can't be what is in you sig... are they? Is your spedo/od corrected for tire size?
For MPG, steve05ram360 should be your search criteria.
He IS the MPG guy. He measures everything.
Oh, and yes, this has been covered quite a few times. search.
 
#21 ·
...um, no. you have a 3.5" exhaust from the turbo down to the muffler, then 4" out.
HHO? snake oil. paper or real life.

stock injectors?

in your sig, what is a SPORTY Sr?

Many things that help MPG don't end up paying for themselves.
the HHO experiment was actual mileage hand calculated, so it worked with his truck.He quit using because kept forgetting to add water every 300 miles and burned it up.

stock injectors

So would it be good to get 4" exhaust all the way"
Sporty is the more expensive one...the 06?

Thanks
 
#10 ·
Yes, 3.42 gears are available, those plus 285-75-17 tires will get you a pretty good drop in rpms. Have a look at this calculator to find out how much of a drop...

Gear Ratio Calculator

Assuming 48re and the above gears and tires, at 80 mph rpms would be 1875 or so...
 
#11 ·
I've got the same gears, 285-75-17 highway tread... it doesn't do what the OP wants. Mine is about the same for mpg as OP.
 
#12 ·
He's in texas doing 80 on the hiway just to keep with the flow of traffic and asked to drop his rpms, taller tires and gears will drop rpms. Mpg at 2200 rpms vs 1800 will be better without a doubt as the motor would be running on a different part of the fuelling map. How much would remain to be seen.

Your truck has 3.42's?
 
#13 ·
if you are asking me... no, got 373. (I guess I could have worded that better)
I get 'keep up with the flow'. I like to go 80 also. But when I do I know to expect the lower range of MPG. I don't do enough highway empty miles to really test things like you. Most of my driving is around town stuff. But still, mine is at 8,250 lbs. aint no hybrid.
His right foot plays more into it.
 
#14 ·
What settings on the Smarty...? I have the SR.
Michelin,s are the ones in signature and are stock 4x4 size on the door, oops, dyslexia, 265/70/17
55-60mph? I'll die of sleep boredom... everything here in west Texas is hundreds of miles away.. I'd crash due to white line fever.
thanks
 
#18 ·
Can't remember the guys name now... the smarty guy... he told me twice the best millage is with my S06 turned up to pl9... and in threads.
sorry, can't help with SR.
I understand about the slower speed but if 55-60 boring, what do you do different at 80? (I ask 'cause you will find you get bored at 80 also.)
Anyway, you want excitement or MPG? Pick one. :grin2:
 
#15 ·
how/where can I get custom tuning?
For example, what tuning?
thanks
 
#16 ·
#17 ·
stock air and stock 4" exhaust
thanks for link...searched lots before and just got more confused :-(
I'll check this out later.

My buddy put an HHO generator on his 1997 4x4 cummins and went from 18 to 25 on paper, but it does nothing to this beast...any ideas? is the computer messing with this?
Is there an O2 sensor anywhere? I have not found one..is it hidden some place?
Thanks
 
#19 ·
...um, no. you have a 3.5" exhaust from the turbo down to the muffler, then 4" out.
HHO? snake oil. paper or real life.

stock injectors?

in your sig, what is a SPORTY Sr?

Many things that help MPG don't end up paying for themselves.
 
#20 ·
The idea of getting there in 5 hours verses 8 hours.. I'm not as durable as I was when the speed limit was 55
 
#22 ·
Some guys claim better MPG after they replace their injector pump. Some after a FASS pump. :spank:
Some after replacing MASS. Some little larger turbo. Some with freespin hubs. Steve will tell you change to a 200 thermostat and warm the air into the engine. Some run all syn oils in everything. Some pull the stock fan and run electric fans. Many install a additional lower air dam in the front. Check for brakes not dragging. Some say lose the slush box for a stick. Tons more on this forum. Other forums say to lower vehicle and cover everything under the truck to be more aerodynamic- like a large skid plate and lower front air dam.
I think it all helps. But after spending $ on gears, hubs, injector pump, etc., you could have just bought more fuel. Not to say if for example your injector pump dies you should get a stock pump. I think I read the ones that are 30% over increase MPG. Upgrading when parts fail is the way to go.
Honestly I'm think the tuning on the truck plays a lot of it. I'm waiting to see how Steve does with his new software.
In the end you are still pushing a 8K brick.
My wife and I have done about a doz vacations where we get into the car and drive. Most has been 9K miles in two weeks. Lowest was 6K in two weeks. I can tell you MPG does increase at the vehicles sweet spot. With these trucks it seems to be about 50-55mph with stock rubber.
I hear the new 1/2 ton diesels get 30mpg... :stirpot:

Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
 
#23 ·
gasjr4wd the reason 50-55 is the sweet spot is not because of the truck its because of resistance itself ... yall can do anything you want but after 55 MPH wind resistance goes UP like CRAZY ...

If you really want better mpg
make the truck more aerodynamic....
make the truck have less rotating mass......
make the truck lighter.....
 
#27 ·
Yep, like I said, it's a 8k brick. (just checked mine, 8250lbs) Bricks aren't exactly known to be aerodynamic.
Makes me think back... my father used to tell me if I wanted to go faster, put more wax on the car.
Wonder if that's why I washed and waxed that car every Friday night? :grin2:
So myth busters showed you could polish a turd, but can you wax a brick into getting better mpg?
:stirpot:
 
#24 ·
Look on the side of the plastic cover over the valve cover... if it says 305HP I think those are 4" exhaust. Cerb think corrected me on this a long time ago but am not sure if it was the SO or the HO in '04 that had the 3.5" exhaust. Either way... 4" with the Aero muffler like I mentioned, then a muffler or kit of your choice behind that. I have a 30" magnaflow muffler and it is just right IMO.

Shanesnofear... The answer to better MPG doing 80 mph is simple... experiment, see the cause & effect and decide on whats best. For the OP... I would recommend the 4" exhaust cutout OR the 7" butterfly vent mod (which I did and tested) on the bottom of the airbox for improved mpg at higher speeds. Last year I had one tank coming down from Oregon where I was doing 70~80 (and 85 for a good 75~100 miles) with the vent in place and still managed 19.0x mpg Had the vent open, 200*f stat in place and partial block on the CAC. If I had a place to test the airbox settings for higher mpg, I'd test it. But, I dont have anywhere to test where I am currently at.

OP, get a way to monitor the OBD port, I use the app Torque with an android phone and am able to monitor critical parameters. Get a block for the CAC and block it so IATs go up +20*f. This will help increase mpg on the hiway. Go +25 or more and the fan will start kicking in. Do the airbox mod I mentioned (linked in the thread linked in my sig) and experiment with different openings of the butterfly vent ($8 at etrailer.com). Plastic for the CAC can be had at Tap plastics and runs about $8/sheet. Hdpe sheet is what you want

http://www.tapplastics.com/product/plastics/plastic_sheets_rolls/hdpe_m_m_opaque/258



 
#25 ·
What is the CAC? New one for me.
I have a scanguage. Will that work for info? Not sure if it has boost.
My truck is the Heavy Duty version.
What is "he 4" exhaust cut out?
New to all of this in the gen 3 trucks
Thanks for the info....
 
#26 ·
CAC = charge air cooler aka innercooler

If you can monitor IATs and CT's at the same time then yeah the scan gauge will do it. You just need to be aware of whats going on under higher load conditions, if you start breaking the 25*f temp differential between the airbox and the IAT sensor then the fan will start to kick on and mpg will start to take a hit... The dash gauge for CT is actually pretty accurate, slow to respond though

http://www.cumminsforum.com/forum/3...rts-discussion/1873074-cheap-airbox-mods.html

http://www.cumminsforum.com/forum/3rd-gen-powertrain/1993130-airbox-mpg-test-experiment.html

exhaust cut outs...
https://www.quicktimeperformance.com/QTEC/

Not sure if I mentioned it in this thread but I believe, opening up the box under the higher rpm/load conditions may improve mpg. When I did the experimenting with the airbox it was clear that with more air into the box the power started shifting up the rpm range. No proof of it, just seat of the pants evaluation. Back then the whole point of the thread was to show others how you can tune your airbox to match your mods.

Now for the exhaust cut out mod (which no-one has done yet), if the bottom of the box is modded such that the 4" exhaust cut out can be mounted and go thru its full range of motion, the flow into the box could be adjusted in the cab and on the fly... around town, close it, out doing 75-80 on the hiway, open it. Its not a cheap mod and its not proven yet. The etrailer butterfly vent is $8 bux and far cheaper to experiment with.
 
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