I recently bought my LLY not knowing much about diesel trucks. People around the house are getting better fuel mileage than me. I get around 14 mpg know. When i first bought the truck i was getting roughly 18-19mpg. I brought it to the shop several times, but they made me feel stupid. It was blowing white and grey smoke when i gassed on it to pass cars and the fuel smelled real rich out the exhaust. I took out my programmer and it doesent smell that bad anymore. I just got it back from the shop on a recall on gauage cluster and it seems to run better, but fuel mileage stinks. I would like any suggestions from anyone. Thanks

mine has all those symptoms and they tell me its fine

Programmer dumps in more fuel for more pwoer.. hense the rich smell.
14-15 mpg is what I have gotten on everyday driving since I bought my truck, it does better on long highway trips, if I keep it under 65 I can pull almost 20 mpg.

I'm getting 14.1 ....................but i haven't used a full tank yet , That was the 1st owners milage

I am getting 18 average, around 17 in town and 19-20 on hwy. I do have alot of after market work though.

Mine gets 13-17 around town, 17-20 on highway deadheading, and 10 with 5th wheel trailer on highway. I lost one mpg when the computer was reflashed to stop smoking problem and another mpg when ultra-low sulfur fuel was introduced.

Before I bought my truck, a lot of Durmax owner sure lied to me about their mileage! Now that they know that I know, most tell a more truthful story!

I must say that I thing the LLY has the poorest fuel economy of all the DMaxes.

Seems like a small price to pay with all the torque and horses under the hood. I get 13.5 to 15mpg in my 3500 and never got any better out of the 1/2 ton I use to drive. I sure can tell the difference when I need to get the job done though!! Mine seem to just keep giving and giving when I need it to, so the trade off is small to me. I added a Juice with Attitude Module to my ride and can get 14 to 20 depends on how far my foot is in it,but the power is un real. Get more Black smoke now but addition of cold air intake should solve that and make all that wasted fuel go to work. I`m told that will help mileage some too.

avg. 15-18. but I drive pretty fast on the freeway. I noticed if I keep it at 2k rpm or lower when cruising, it get's best mileage. I've seen 1-2mpg drop from just 300rpm over 2k. for extended time periods.

Are you hand calculating your mileage. The hypertech is a very safe tuner and you should be getting better mileage with it. When was the last time you changed you fuel filter? Is it getting better mileage after the programmer was downloaded?

I changed my fuel filter about 3K and also had oil changed and tranny serviced. Not to cheap to do all that. This morning i noticed that my fan would kick on and off every few seconds. I'm wondering if it 's not staying on all the time i'm driving. The engine was cold this morning when i noticed. I really did not notice a difference in milagr wit or without Hypertech in.

Is your programer set for the right tire size ?? I see differences between 245s and 265s. With same set up on programer. Just curious !!!

Steve,

Things to remember:

Tire pressure - keep it at 65/80, or 80/80. The higher tire pressure, the less rolling resistance... the better the fuel economy.
Stock tires look puny, but they max out on the fuel economy. Bigger tires and lift kits look great and can enhance off-road capabilities, but all at the cost of fuel mileage.
TxC's CAI with a good clean stock filter will do everything you ever need for cold air, and will add mpg's (added 2+ to my truck) for all of $60. Best money you can spend.
Fuel additives - I use Power Service. Some claim as much as 2 mpg's; I see less than that. YMMV...
I don't know Hypertech's tuners; I have a Predator. Predator has an economy tune - +65 hp - that added a couple mpg's to my truck.
Blocking the EGR/reroute the PCV will at the least keep you from dumping sludge back into your intake. I've not been able to tell, but some claim mileage improvements.
Custom exhaust (4"), especially w/cat delete, is supposed to net you additional hp and theoretically additional mpg's (if you can keep yer foot out of it). Besides gauges, this is my next step.
Bed cover - the jury is still out on mine, but again... theoretically, a good bed cover should improve aerodynamics thus mpg's. I'm beginning to believe that unless you get a rigid one, you won't gain anything. :(
Driving habits - you can do all of the above and more and still drive like a nut and get lousy mileage. Lots of tips out here and in other places on the 'net. 2k rpm's, learn to coast, don't drive up to stop signs/lights, etc.You can see my mods below. When I keep my foot light on the skinny pedal, I get 15-16 in town and 22+ unloaded on the highway. My goal is still 25 mpg on the highway; I'm not there yet, but I am convinced it is achievable. Good luck!

"avg. 15-18. but I drive pretty fast on the freeway. I noticed if I keep it at 2k rpm or lower when cruising, it get's best mileage. I've seen 1-2mpg drop from just 300rpm over 2k. for extended time periods"

Ditto what TP said above in quotes...

I'v driven my 2005 2500 2wd silverado 53,000 miles since I bought it new in July 2005, 15-18 best discribes my fuel milage...

When I tow my #5000 racecar on an open trailer to go racing, 13-14 is the average, I am sure if I slowed down to say 60 mph, it would get 15 mpg towing, it's just too easy to cruise in the 65-70 mph range in this truck...

My old 1500 gas truck got 10 mpg towing, on a good day, and it was gutless. It got 17 normal driving. It could not do near what the Duramax is capable of, and the Duramax weights about #2000 more than the old gas truck. So the Duramax wins against the old gastruck, hands down, no doubt...

My neighbor just bought a 2003 Dodge 3/4 ton crew cab 2wd with the cummins inline six deisel...

He always mentions his 18-20 MPG or whatever mpg he gets, I get tired of hearing it...

If I have to drive a Dodge to get the cummins inline six cylinder deisel, to get better gas milage, then I guess I'm stuck with 15-18 MPG, cause I'm not going to drive a Dodge, period...

My buddy just bought a new Dodge Cummins and he's getting terrible fuel economy. He's seeing 12-14 mpg tops. He had an older one that got pretty good mileage, but his new one absolutely sucks fuel.

YMMV...

Can`t Hammer Cummins too much.... They are in American Trucks. What psss me off is when Toyota and Nissan Drivers want to compare what they drive to my TRUCK !!!!!!
If you want to get 18-20 Mpgs fine. If you want a Real American Power Plant that "Can and Will " get the job done there is none better on the road than Duramax. Just how much can you get fron a rice burner anyway ? Let alone ridding in one. I`d rather ride a bicycle than be cramped into one of those things.Silverado,Ford,Dodge, I`ll take any of them, but rather drive a CHEVY !!! Besides I can get better mileage with Mods and a little driving sense. Plus every Mod you put on these babies alos brings on the Horses and tons of torque.. Sorry guys but not sorry in a way too...

Tom2500HD If your Max is so bad and you think other wise all you need to do is drive a 2500hd gasser and get back at us..........Then you'll know what milage is all about are company has three and they never get above 12mpg on there best day. other wise ther 10 and 11 at best. And my 05 must be poor than cuz i get 26.4 out on the highway If as you say the LLY's are the poorest i wonder just how good everybody else really is?

.......... If you want a Real American Power Plant that "Can and Will " get the job done there is none better on the road than Duramax..........

The duramax is an Isuzu motor.....aren't they a Japaneses company?:eek:

The profit stays right here in the US and helps boost the econmy here instead of going stright sea's. It is just like the a Honda plant here in the US, sure they employ some Americans but at the end of the day the majority of the profit goes right over sea's.


Back to the topic at hand, I get about 25mpg on the highway and 18ish in the city. Very happy with the milage. My old 99 s-10 4x4 got 15mpg and was only 3,200lbs...

Light foot on the gas and keep it at or under 2000 rpm. I could easily get 3-4 mpg less by driving harder. Also, the defroster will run the A/C compressor and drop the mileage .5-.9 mpg. I'm getting 18 right now and it's damn cold out.

I just got the average fuel mileage off of my '05 LLY, and driving city/highway stop and go between 15 and 60mph when I got home I had averaged 20.9 MPG, considering I have a 6" lift and 325/70-17's I think I am doing pretty good. I Have the banks six gun system with Banks Monster exh, and Intake running amsoil 15w-40 with duel filter bypass. I drove with my Banks on setting 6 driving civilized, with the banks on setting 2 on the same trip I averaged 18.8 last week. The Duramax obviously has the potential to get great mileage, I think how far your foot is in the throttle is the main factor.
Also in the next few days, I will be installing a PPE EGR Delete intake manifold, and switching my transmission fluid over to amsoil torque drive, and I will re clock it and see if there is any noticeable difference

With the '05 in my sig, I get 15, give or take a mpg.

Later

I just got the average fuel mileage off of my '05 LLY, and driving city/highway stop and go between 15 and 60mph when I got home I had averaged 20.9 MPG, considering I have a 6" lift and 325/70-17's I think I am doing pretty good. I Have the banks six gun system with Banks Monster exh, and Intake running amsoil 15w-40 with duel filter bypass. I drove with my Banks on setting 6 driving civilized, with the banks on setting 2 on the same trip I averaged 18.8 last week. The Duramax obviously has the potential to get great mileage, I think how far your foot is in the throttle is the main factor.
Also in the next few days, I will be installing a PPE EGR Delete intake manifold, and switching my transmission fluid over to amsoil torque drive, and I will re clock it and see if there is any noticeable difference
Was that with the DIC or hand calculated? If you are using the DIC it's wrong due to the Banks.

Tom2500HD If your Max is so bad and you think other wise all you need to do is drive a 2500hd gasser and get back at us..........Then you'll know what milage is all about are company has three and they never get above 12mpg on there best day. other wise ther 10 and 11 at best. And my 05 must be poor than cuz i get 26.4 out on the highway If as you say the LLY's are the poorest i wonder just how good everybody else really is?
Same question to you. Do you hand calculate or go by the worthless DIC that is inaccurate with a programmer or box?

I have to agree with slayer's questions. My DIC will read in the high 20's while the hand calc. ends up in the mid to high teens.

Mileage Spreadsheet (http://spreadsheets.google.com/pub?key=pfK1rhg6Fre-grPfB9ByMIA)

That's nothing. Last long trip I took, DIC reported nearly 32 mpg! Actual mileage was more like 20. Ya definitely gotta hand calc... :HiHi:

Problem with my predator is that I tow 5k-10k regularly. If I am not mistaken, I am supposed to stay on the tow tune 45hp or I will be towing too heavy for the 65hp tune. The dic makes me feel good seeing as much as 21 mpg on the readout, until I scroll through and see that I only get about 300 miles on 3/4 tank...then I feel crappy again....what to do?

-Welder

Welder, that is still 15 MPG. I think people have some unrealistic expectations because of what some people post on here. If you got over 15 MPG towing, I would be amazed. Hell, I am amazed you even got 15 when towing. That's what I get on a good day!

Where did you get 15mpg? 3/4 of 34 gallons is 25.5 gallons. 300 miles/25.5 gallons is 11.764!

-Welder

I have a 26 gallon tank, my bad!

However that is about what I get while towing... 7-8 in the mountains, 10-11 on the highway at 60-65

2004.5 LLY 114K and since new I have got about 17 town and 18.5-19.5 on the highway. That is with or without the programmer. Towing my goose neck with 15K on it and running 65mph I get 11-12. With my 26 ft 5th wheel I get 10-14 depending on wind and speed.

You have to also remember that you will be getting winter fuel and that can take 10% off the economy real easy.

I couple of months back I put a bed cover on and that brought the mileage up at high speed.

I very happy with it because it ways 7200 lbs. and has all the power I need. I can't think of any half ton that can do it.


Greg

I couple of months back I put a bed cover on and that brought the mileage up at high speed.

Greg, what type of bed cover did you get? I was hoping to improve my mileage by adding a bed cover, but I bought a cloth bed cover (see details in my sig). The few tests I did were at the beginning of winter fuel (I think), so I'm not ready to accept the results, but I did not see any gains. I've been watching my bed cover in the rearview mirror, and while it is very taunt and has some rigid supports and fits tight to the bed, it still flaps a bit... which I suspect isn't helping things.

From what I recall regarding aerodynamics, I'm betting that hard bed covers may be required for the best results; I'm hoping that they're not required for any positive results.

Greg, what type of bed cover did you get? I was hoping to improve my mileage by adding a bed cover, but I bought a cloth bed cover (see details in my sig). The few tests I did were at the beginning of winter fuel (I think), so I'm not ready to accept the results, but I did not see any gains. I've been watching my bed cover in the rearview mirror, and while it is very taunt and has some rigid supports and fits tight to the bed, it still flaps a bit... which I suspect isn't helping things.

From what I recall regarding aerodynamics, I'm betting that hard bed covers may be required for the best results; I'm hoping that they're not required for any positive results.


I would have to go look at it to see what brand it is, but its a soft cover. I had it on for about 4 tanks of regular fuel before winter blend came in. Anyway I got between 19-20 at 75mph. At that speed in the past it would drop to about 18-18.5. I would never have guessed it would make a difference. I bought it because I always carry things that I don't want to get wet, economy was not even thought about. When we get back to good fuel in March or April I will see if it was just a fluke or not.

Greg

Was that with the DIC or hand calculated? If you are using the DIC it's wrong due to the Banks.
I have hand Calculated, and used the DIC, I have installed a true speed speedometer re-calibrator, so the DIC shoud be pretty close. I hand calculated with the Banks over a 3500+ mile trip driving it like I stole it, and I was averaging right around 17, that includes racing it at 105+ so My guess is that this avarage is pretty close. Now when i did this avarage of 20.9 I had my banks on setting 6 and was driving extra conservatively. On the same trip If I drive it like I like to.. it gets around 13.5-14.5. Thats why I was saying that the fuel mileage greatly depends on how far your foot is in the pedal. I also just installed the PPE EGR delete intake manifold yesterday, so on my next tank full I will see if it makes any difference.

I have hand Calculated, and used the DIC, I have installed a true speed speedometer re-calibrator, so the DIC shoud be pretty close. I hand calculated with the Banks over a 3500+ mile trip driving it like I stole it, and I was averaging right around 17, that includes racing it at 105+ so My guess is that this avarage is pretty close. Now when i did this avarage of 20.9 I had my banks on setting 6 and was driving extra conservatively. On the same trip If I drive it like I like to.. it gets around 13.5-14.5. Thats why I was saying that the fuel mileage greatly depends on how far your foot is in the pedal. I also just installed the PPE EGR delete intake manifold yesterday, so on my next tank full I will see if it makes any difference.

HHH The DIC will not read anywhere near correct if you have any tuner installed. No matter if your speedo is right on or not.

Zack

just would be nice if tyhese trucks would consistently would get 20mpg

I have hand Calculated, and used the DIC, I have installed a true speed speedometer re-calibrator, so the DIC shoud be pretty close. I hand calculated with the Banks over a 3500+ mile trip driving it like I stole it, and I was averaging right around 17, that includes racing it at 105+ so My guess is that this avarage is pretty close. Now when i did this avarage of 20.9 I had my banks on setting 6 and was driving extra conservatively. On the same trip If I drive it like I like to.. it gets around 13.5-14.5. Thats why I was saying that the fuel mileage greatly depends on how far your foot is in the pedal. I also just installed the PPE EGR delete intake manifold yesterday, so on my next tank full I will see if it makes any difference.
The speedometer re-calibrator will not fix the DIC. The DIC is off due to the fuel volume being changed and the DIC calculation table not being re-calibrated.

What is your average MPH per tank when driving conservatively? If it's at about 39mph and over you are probably doing more highway than city so the mileage you are getting makes more sense if that's the case.

well i was happy with my 14.5mpg on the 90 horse tune on my tripledog, but thats using the DIC. I will hand calc a tank full and post back, Does the crewcab shortbox have a 26gallon tank?

Yes, the tank is 26 gallons

The speedometer re-calibrator will not fix the DIC. The DIC is off due to the fuel volume being changed and the DIC calculation table not being re-calibrated.

What is your average MPH per tank when driving conservatively? If it's at about 39mph and over you are probably doing more highway than city so the mileage you are getting makes more sense if that's the case.


I would say that my average would be around 45, I was just saying that it included city driving, for that test. And about the DIC I dont know anything about the fuel volume and calculation table, but I hand calclulated yesterday after I had filled up and the DIC was off .8 to the minus side of what my hand calculation was..??

It sounds like you know your stuff, So i'll ask what may be a stupid question. The fuel volme is not going to change unless you are driving with the pedal to the floor, there is no need for extra fuel if you are driving normal is there? I dont know specifics abou these tuners But I do know that there is a lot of difference about how the banks achieves its power verses the others, every other tuner will dump extra fuel and thats where you get the cloud of black smoke, and the Banks has nothing at all. And I can vouch for the edge cuz I used to have it on my truck, and it looks like a steem engine behind me... anyways. Hope to hear back from you.

The tuners change the ammount of fuel over the whole throttle range. If they only changed at WOT you would get near stock acceleration and then a huge surge at the end of the pedal.

This is why you will sometimes notice that the pedal is a lot "touchier" when you install a chip in you truck.

There is a curve for the ammount of fuel deliverd at any throttle position. To keep that curve smoothe, when they increase the WOT fuel delivered, they also increase all the other ammounts in the table so there is a nice curve up to WOT. Except for idle of course, which should stay the same.

Hope that makes sense...

Here is a an awesome technical drawing :D

alright, makes sense!

Here is a an awesome technical drawing :D

What is the Sotck setting? Is that a new feature I'm unaware of? :D

:)

My LLY w/65hp Predator tune will only net me about 12-13 in town (lots and lots of 2 and 3 mile trips with a little bit of idling at each end of the trip...it sucks living in town while going to college:rolleyes:).

On the highway, I can only achieve about 16-17mpg at 70-75mph, but my last trip home (140 miles, about 95% interstate) I set the cruise at 65 and it's looking like I'm going to squeeze about 19 or 20mpg out of this tank. I've found that the predator usually throws the tank average off by around 2 or 3 mpg and the DIC is reading 23.5 for the trip home and back.

Ignoring fuel economy usually nets me about 16mpg back home (lots of country roads, not much town driving).

Update: Apparently, the DIC is off more now than it was. I got 18.49mpg for the tank. 344 miles driven and 18.6 gallons of fuel. I figure that's not too bad for winterized ULSD fuel.

That is also about the best I can get, driving 65 or lower. Mine is a 4x4 3500, so it weighs a bit more.

I keep careful track, and calculate every tankfull.

My DIC running stock is off by about 6% - it shows 12.6 l/100 km, and calculated average over several tankfuls is 13.4 l/100 km average driving here on the island this winter.. That works out to 17.6 US mpg.

I rarely use the truck for short trips, most trips are about 50-100 miles, but there is maybe 10% city driving included in that average.

Programmer dumps in more fuel for more pwoer.. hense the rich smell.
14-15 mpg is what I have gotten on everyday driving since I bought my truck, it does better on long highway trips, if I keep it under 65 I can pull almost 20 mpg.

Exactly what I get, glad to hear someone else getting the same.

Speaking of weighing more with a 3500, anybody know the difference in curb weight between a 2500 and a 3500 ?

Yes, the tank is 26 gallons


I do not understand how I run the tank dry, pretty much, and fill it up. and it will only take 20 gallons? how can this be? I am afraid to run completely dry to see if the gauge is off that bad or not....anyone else have such a thing?

I do not understand how I run the tank dry, pretty much, and fill it up. and it will only take 20 gallons? how can this be? I am afraid to run completely dry to see if the gauge is off that bad or not....anyone else have such a thing?

My guess is that they want to scare you into the gas station before you actually run it out of fuel.

ULSD is the problem. I constantly get 19.3mpg! Get injectors or a chip that boosts turbo pressure and injector pressure.

Beats driving a furd. My neighbor has a 1100$ truck payment on his new furd diesel. He's getting 7 mpg!

Try Too Reset The Meter When Your Truck Is All Warmed Up

my 05 DMaxx in a 2500 4x4 ext cab and 8 ft box has gotten 18.5 to 20 mpg since I have owned it, 35 k on the clock now

it's stock just the way it came from the factory

Just as an update, I have now got my EGR Delete intake manifold on, and have now recalculate my mileage. Driving on the interstate averaging between 55-75 I got around 18 MPG mind you that is with a 6" lift on 325/70r-17's, and driving back were running late and I was running upwards of 85 for the last 160 miles and we still got 17.5, that is hand calculated my DIC said 19.2 for the first trip and 19 for the second, I went 393 mile s on the first trip and 403 miles on the second, so I am happy!!! and that is running it untill the light comes on requiring around 22.something gallons to fill it back up.oh and I was running the banks on level 6

i get 18 at the most on the highway with my edge with juiced

Im now towing a 6300 # mid hieght 5th (weights unloaded) thinking of moving up to a 8100# mid hieght, well this 1800# be noticed in performance or mpgs .truck pulls the one we have very easy but the mid hieght kills my mpgs to about 12ish,just wondering how much of a facter the wieght would be??

I get around 12 towing 5k trailer and 9k skidsteer. Pretty hilly around here so I was surprised that it was that good.

I also tow a 10.5k skidsteer sometimes and you can really tell you are pulling the extra 1500# behind you.

oops ;was trying to start thead ,must have hit post reply ..sorry guys

I also tow a 10.5k skidsteer sometimes and you can really tell you are pulling the extra 1500# behind you.
thanks for the info was hoping for alittle to no diff.,now is that 10.55k thing on the 5k trailer that would be about 15k total is that rite ?

Help!!!My buddy has an 05' LLY CC with 285' BFG's and a Edge Juice W/***...He is only seeing 9 mpg empty driving back and forth to work...It is goin in today to see if Mr. Goodwrench can figure it out...They are going to try to replace the wiring harness??? It sounds to me like a fuel delivery problem injectors etc...But I wanted to see if you guys had any other ideas

Try a search on injector wireing problems.Seems like injector wireing on number 1&7 was a problem.


Help!!!My buddy has an 05' LLY CC with 285' BFG's and a Edge Juice W/***...He is only seeing 9 mpg empty driving back and forth to work...It is goin in today to see if Mr. Goodwrench can figure it out...They are going to try to replace the wiring harness??? It sounds to me like a fuel delivery problem injectors etc...But I wanted to see if you guys had any other ideas

[quote=rockinW;2425987]Im now towing a 6300 # mid hieght 5th (weights unloaded) thinking of moving up to a 8100# mid hieght, well this 1800# be noticed in performance or mpgs .truck pulls the one we have very easy but the mid hieght kills my mpgs to about 12ish,just wondering how much of a facter the wieght would be??[/quote

I tow a 33 ft travel trailer and get around 11-12 mpg. The variable in this is where and how fast I drive. I keep it under 65 and I travel mostly from SC to PA for hunting trips. The mountains are no problem for it but I do see a drop in fuel economy. I hand calulate no DIC it's a girl.

My DIC mileage used to be about 2 mpg higher than what I was actually getting but I recently adjusted it through EFI live to try to make it more accurate. I've been driving around for the past few days on my 100hp tune and my DIC currently says my average is 23.5 mpg (I reset it at my last fill-up). When i fill up next I'll know how much more accurate I made it but I'm getting at least 21.5 mpg considering the most i've seen it be wrong is 2 mpg and I ajusted it quite a bit. I have a very heavy foot and switch it to my hot tune to pass people, blow smoke, or blow away Mustangs at the redlights and have been doing all those things on this tank of fuel as well.

update on mileage, after replacing my fuel filter, I have seen dramatic fuel improvements.. since last time I calculated my fuel mileage I have jumped from 15 city to 17.2 city, and as high as 21.5 highway, my DIC has been around 1.2 miles off, and driving around town, back and forth to work it has been reading 18.4, out on the open high way doing 65 avg, it was reading 22.8. The averages that I am getting are hand calculated just for clarification. When I replaced the filter it was like someone had put a hand full of dirt in it, it was horribly stopped up. So much as it would throw a Code 41 on my banks when i would really get in to it, which is what threw my attention to the fuel filter, as the code is for low fuel rail pressure. Any ways, if you are getting horrible fuel mileage check you filter..