Why is my 2004.5 LLY so hard on fuel compared to my 2003 LB7?


I'm actually scared to calculate it because I know it is around 10mpg towing my 8000lbs camper. http://www.dieselplace.com/forum/smileys/Confused.gif


It uses almost 50% more fuel as my old LB7 http://www.dieselplace.com/forum/smileys/Confused.gif


Any theorys? Cat? EGR? Turbo?

Maybe your right foot? Just a thoughthttp://www.dieselplace.com/forum/smileys/Cool.gif

Nope. Set the cruise 68 mph. Never had to pass anyone or anything. Set the cruise and go. On the way up there I drove 200 miles with my camper and 15 more without and I was on E. Filled up and it took 20 gallons... No kidding. On the way back it got slightly better but not enough to jump up and down about. My old truck would have done almost double that.


I sure hope it gets better really soon.



The only difference in configurations between this truck and my old one is that my old truck had synthetics all the way around where this truck still has stock fluids. I'll be changing the diffs to synthetics asap and changing the engine oil but sticking with dyno for a bit yet.


Maybe the carbon metallic has more wind resistance. http://dieselplace.com/forum/smileys/HiHi.gifEdited by: Max Power

MP


Lets get some wax on this babyhttp://www.dieselplace.com/forum/smileys/Embarrased.gif

Max,

I would think the cat would have some negative impact, the question is, how much? Based on previous posts by others, I am assuming 1/2 mpg. However, I think some prior posts were estimating as high as 1 1/2.

I thought the EGR only came into play at around idle rpm. If that is the case, then I have been assuming it has no mpg impact while cruising.

After reading all of the fuel milage posts for the last several month, I would expect an LLY to get 13 mpg or a little more, pulling a conventional 8,000 lb travel trailer on a mostly flat route. If I were only getting 10 mpg, I would ask the dealer to do a scan on the injectors, and check out sensors that could impact milage.

Some folks swear their truck's milage gets better with every mile and some say there is no difference after break-in. I am still undecided. After 5,000 mile, mine still runs (power and milage) basically the same as new. I am not expecting any drastic fuel milage improvement as the miles increase. Sorry.

Does the new truck have more drag than the old truck? (How does it coast on a known downgrade compared to the old truck?) I have been wondering if the large variations in fuel milage between individual trucks, as reported on this site, could be due to variation in drag or rolling resistance between the trucks. I am planning on doing some comparisions between my 2004.5 LLY and a similar 2003 that is getting better mpg. As I mentioned in another post, my 2004.5 doesn't build near the downhill coast speed that my previous 1997 gasser got. I was told that diesels do not develop compression braking like a gas engine, so I was expecting higher downhill speeds rather than lower speeds. I am thinking my Duramax must have more drag/resistance in one or more of the components.

I always find your posts very informative and am looking forward to learning what you discover.

Good Luck.

Is it possible that this is where they got the extra 10hp from?


How about LLY injectors? are they different from LB7's? or possibly redesigned due to earlier failures?


I've been wondering some similar issues raised, especially reading about big differences in fuel economy from truck to truck,





Rob

Max,


Your numbers don't sound right to me either. I towed more than 21,000 combined pounds over 3,000 miles after only having about 1,000 miles on my truck in January. I didn't tow at 68 MPH, but more like 55-60, over the Rockies, too. I got about 12-12.5. My mileage, like BH in AZ, hasn't really changed since I got the truck, maybe 0.5 MPG increase TOPS. My power hasn't seemed to change either, although I do enjoy it more now.


I would bet there are a combination of things going on:


1. Your speedo may be off the opposite direction as your old one (say your actual speed is 65, the old speedometer said 66, the new one says 64, difference 2 MPH, or over 3% difference, which might make 1 MPG). I know that the faster I go over about 60, fuel economy REALLY starts to suffer towing.


2. BH in AZ is on to something with the rolling resistance. This is a pet project of mine, and I know that my LLY slows down very fast when I let off the accelerator, either the engine brakes it better or it has significantly higher rolling resistance. Who knows, maybe 0.5 MPG? Does the truck feel like it slows more easily than your '03?


3. Synthetics. You KNOW that has to make a difference, maybe another MPG? 1.5?


Total it up and your out almost 3 MPG just from three little things I could think of off the top of my head.


What do you think?
Dennis

As far as rolling resistance, it feels exactly the same as my old one.


I don't think synthetics will make 1.5mpg improvement. I'd be surprised to see any measurable improvement, but I guess we will see.


I think some of the difference might also be the fuel guage. The new fuel guage seems to me more linear. My old one used to hang above full for 50-75 miles. The new one moves off of full right away. This gives the illusion of poor fuel economy but this could also be due to poor fuel mileage. http://www.dieselplace.com/forum/smileys/Confused.gif

"If I were only getting 10 mpg, I would ask the dealer to do a scan on the injectors, and check out sensors that could impact milage."


BH - would someone notice a problem possibly if it were an injector ? ive often wondered about this and want to do a scan on the injectors again to see where there at. Does anyone know what the injector range should be on the LLY ?

Where you in tow mode on the transmission? From what I understand it is not desireable from a MPG stand point and unnecessay unless you are towing at least 75% of maximum.


I have noticed that MPG really drops above 60 mph without trailer. Will have to see what it is like with my 6000 lb trailer pretty soon. Maybe the Allison programing is the cause?

I was not in t/h mode. Irregardless, I have tried it both ways with my LB7 and it didn't make any difference. With my LB7 I could tow 70mph+ and still get almost 50% better mileage.

As far as rolling resistance, it feels exactly the same as my old one.


I don't think synthetics will make 1.5mpg improvement. I'd be surprised to see any measurable improvement, but I guess we will see.


I think some of the difference might also be the fuel guage. The new fuel guage seems to me more linear. My old one used to hang above full for 50-75 miles. The new one moves off of full right away. This gives the illusion of poor fuel economy but this could also be due to poor fuel mileage. http://www.dieselplace.com/forum/smileys/Confused.gif





Maybe not. Just a stab in the dark, but there has to be a little difference. What do you think about the speedo correction factor? I would bet if you come up with enough little factors, they add up to bigger differences in mileage. Heck even the weather could be making a difference, warmer air, not as much O2 per volume, higher humidity. . . who knows. . . unless something is wrong with it, but I doubt seriously if something was wrong with it you wouldn't know it by now. . . you thought it had pretty good power from the start.

I think the speedo is pretty close. I understand what you saying, and it crossed my mind as well. If we were talking about 10%, maybe even 20% I wouldn't be concerened. But 50% is too much. I am going to check into the small things like you mentioned and hopefully it will improve a bit. Honestly I doubt I will get more then a 5-10% improvement.


I talked to my dealer today and he says that quite a few are complaining that the LLY is no where near what there LB7 was. He is going to check into it with GM. I doubt he will get anywhere either. He suggested that perhaps that fuel mileage is down due to emissions related programming. He said that maybe GM will offer updated programming that doesn't meet emissions but does improve economy. I'd be all for that but I knowing GM I think it will be a long shot.

Has anyone upgraded their exhaust and noticed an improvement in fuel mileage?

How about the TTS tow tune? Any improvement?

Not sure how GM does business, but with Federal mandates on emissions, I would tend to doubt they will offer updated programming. Maybe they will be allowed to do it on Canadian registered vehicles, but I would bet anything in North America will meet U.S. emissions. Would be nice though. I heard someone post recently that they used an LB7 downpipe on an LLY, but this was fairly recent and I was going to wait to see if any codes popped up before I tried something like that. If he doesn't get any codes, the Catalytic Converter and EGR could be preventing some of the great mileage you were seeing on your '03.


Dennis


P.S. I was a little confused by your fuel meter statement. I understand what you are talking about (I've had some [old Ford] that you can go half the tank on before it moves, then drops like a rock), but you've actually calculated both and know what the difference in mileage is, right?

Max Power, Im thinking the same as you cuase my truck gets about the same pulling a trailer. If i could drive 55mph like biimpala I too could prolly muster 12-13 pulling mpg but I cant drive that slow and the speed limits around here are 65-70 . The faster you go the worse they get !

so whats the deal with the CAT ? im in CA - can i remove the cat and still be able to register every year or would i be screwed in the area. I had been thinking of removing it regarless of codes but wasnt sure on the other parts, ie running conditions and emissions

Another thought. Are you running the juice at the same level?


That might be making a difference, too.


Dennis


FASTOYS,


Believe me it was hard. I like to speed (who doesn't?), but that was the first time I'd ever really towed anything, and with a brand new truck and trailer with a rookie behind the wheel, I wasn't going to take any chances. I felt like I was in PARK sometimes.http://www.dieselplace.com/forum/smileys/Big Smile.gif I got about 12.5 with over 21,000 lbs, too. Big difference between that and Max Power's 8k trailer (I figured my trailer loaded was somewhere around 14k).


Dennis

"If I were only getting 10 mpg, I would ask the dealer to do a scan on the injectors, and check out sensors that could impact milage."


BH - would someone notice a problem possibly if it were an injector ?* ive often wondered about this and want to do a scan on the injectors again to see where there at.* Does anyone know what the injector range should be on the LLY ?


tbone1227: There have been several postings of trucks getting declining fuel milage, and the injector balance range was out of spec. However, they also had complaints of smoke and rough idle.

Here is a post that discusses balance range, but it appears to be for the LB7.
http://dieselplace.com/forum/forum_posts.asp?TID=8053&KW=balance+range+injectors

Here is another thread that provides a range for what I assume is the LLY. See the note from maynard9089, dated 07/20/04.

http://dieselplace.com/forum/forum_posts.asp?TID=9429&KW=balance+range+injectors&TPN=2

I only checked it on the trip there. 200 miles, 20 gallons. 10mpg http://www.dieselplace.com/forum/smileys/Disapprove.gif


On the way back I had the juice removed and it was slightly better going by the gage but I never calculated. I also had a tail wind all the way home. I doubt it is any better then maybe 11 or 12mpg.

BH - thanks for that info, im going to check it out. Anyone have info on the cat removal for me in CA ??

3. Synthetics. You KNOW that has to make a difference, maybe another MPG? 1.5?
What do you think?
Dennis

I'm not convinced synthetics make any difference. I saw practically zip change in the milage when I went from Rotella-T 15W-40 to Rotella-T 5W-40 synthetic. Next time I'll try Royal Purple for a true synthetic.

Jim

Jim,


Well, okay, I wasn't speaking from experience there. Everything I've ever heard is that synthetics get better mileage. It could be that your story is the truth and all those guys that spent a bunch of money on synthetics wanted something to say for putting it in their vehicles.


"Hey, I just spent a bunch of money on this oil, it's got to be better!"


Good to know, though,


Thanks,
Dennis

My mileage is the same towing my 11k# fiver with my new truck as it was with my (lwb cc 4wd) 02 model DA,9-10 mpg.Unloaded is about the same also.LLY pulls better stock but the better shifting tranny could be altering my perception.

I am getting 10 mpg with a 12k 5th wheel. The reason that the truck does not seem to coast as well as the old lb7 is the variable vane turbo. It doesn't shut when you let up, but it comes close. Rolling resistance would be air pressure.





I believe the fuel mileage is a result of programming for quiteness and emmisions.

2004 Dmax: I have new injectors, removed my cat, have my egr unplugged, 4" exhaust, synthetic all around, edge w/ attitude set to mileage and run about 65# tire pressure. Everything you can possible do for mileage and I still get 12.5 mpg. I tow a 34' travel trailer and get 10.5 mpg. What the F!CK!!!!!!!!! My buddies 01 get 18.5 mpg towing the same trailer and has gotten up to 26 mpg unloaded!!!!!! If you have a LB7, keep it!!!!! Chevy needs to convert back.


Frustrated in Portland.


BW

I guess that is the advantage of going from my old 1995 C3500, cc, lb
to my 2004.5 4x4 2500HD, CC SB. Mileage went from 6 to 12 pulling
my 6,000 lb trailer. I was ecstatic!!!

2004 Dmax: I have new injectors, removed my cat,
have my egr unplugged, 4" exhaust, synthetic all around, edge w/
attitude set to mileage and run about 65# tire pressure.
Everything you can possible do for mileage and I still get 12.5
mpg. I tow a 34' travel trailer and get 10.5 mpg. What the
F!CK!!!!!!!!! My buddies 01 get 18.5 mpg towing the same trailer
and has gotten up to 26 mpg unloaded!!!!!! If you have a LB7,
keep it!!!!! Chevy needs to convert back.


Frustrated in Portland.




BW,



I know this mileage debate will forever be a subjective subject but it
sure sounds like you still have a mechanical issue with your
truck. I don't have a DIC (http://www.dieselplace.com/forum/smileys/hihi.gif) so I
hand calculate my MPG's everytime. For consistancy sake I fill my
fuel tank all the way to the neck everytime and over 1400 miles since
new I've gotten 16.5 - 17 MPG each fill-up driving 50/50
city / highway. I've driven it hard and driven it soft and still
come up with the same MPG's. Haven't taken an extended highway
unloaded trip yet to see what it gets for highway MPG's.



Totally stock - 55 PSI with Stanadyne.



Just some info, not to further frustrate you but to maybe give you a push to find the cause.



Rob

My Dic shows about 17 -17.6 on average mpg with just the Edge on 4. Does the Edge throw the DIC off much? This was NOT an extended drive it was just a 50 mile short drive to see what it said.Edited by: FASTOYS

I'm knocking down 15 MPG city, 19 MPG highway (at 75 MPH) hand calculated. How does this compare to other LLY's? Have not had a re-flash done at the dealer (truck was built 6/04) and it is bone stock. 55 PSI all around in the tires. 2,500 miles on the odometer so far.

Why is my 2004.5 LLY so hard on fuel compared to my 2003 LB7?


I'm actually scared to calculate it because I know it is around 10mpg towing my 8000lbs camper. http://www.dieselplace.com/forum/smileys/Confused.gif


It uses almost 50% more fuel as my old LB7 http://www.dieselplace.com/forum/smileys/Confused.gif


Any theorys? Cat? EGR? Turbo?





Max,


You're absolutely right. My 100% stock 2005 GMC gets 8 - 9 mpg pulling my 8,500lb fifth wheel camper @ 65 mph. (I've pulled it four or five times now & checked mileage each time.)


Unloaded city - 13; Unloaded highway - 16.


Todd

Why is my 2004.5 LLY so hard on fuel compared to my 2003 LB7?


I'm actually scared to calculate it because I know it is around 10mpg towing my 8000lbs camper. http://www.dieselplace.com/forum/smileys/Confused.gif


It uses almost 50% more fuel as my old LB7 http://www.dieselplace.com/forum/smileys/Confused.gif


Any theorys? Cat? EGR? Turbo?





Max,


You're absolutely right. My 100% stock 2005 GMC gets 8 - 9 mpg
pulling my 8,500lb fifth wheel camper @ 65 mph. (I've pulled it four or
five times now & checked mileage each time.)


Unloaded city - 13; Unloaded highway - 16.


Todd



I sure hope I don't eat my words later but.......I can't get my truck
to get that low of MPG's when not loaded. ?????????
That's got to be some hard city driving time.



On edit: I see from your profile you have 265's - that's not 100%
stock. Did you account for the bigger tire size when calculating
MPG's??

Edited by: skoryaro2

I'm knocking down 15 MPG city, 19 MPG highway (at 75
MPH) hand calculated. How does this compare to other LLY's? Have not
had a re-flash done at the dealer (truck was built 6/04) and it is bone
stock. 55 PSI all around in the tires. 2,500 miles on the odometer so
far.





I've been following the mileage threads pretty close - sounds about
right. Seems like there is less of a discrepancie with people posting
'05 MPG's compared to the earlier LLY's.





Just a thought...

http://www.dieselplace.com/forum/smileys/smiley19.gifI wish I had kept my LB7. There are not enough positive differences in the LLY for me vs the LB7. I wish I had my LB7http://www.dieselplace.com/forum/smileys/smiley19.gifhttp://www.dieselplace.com/forum/smileys/smiley19.gif

Oh - I don't doubt that the LB7's were better. Most multi-owners seem to agree on that.

I'm knocking down 15 MPG city, 19 MPG highway (at 75 MPH) hand calculated. How does this compare to other LLY's? Have not had a re-flash done at the dealer (truck was built 6/04) and it is bone stock. 55 PSI all around in the tires. 2,500 miles on the odometer so far.

I've been following the mileage threads pretty close - sounds about right. Seems like there is less of a discrepancie with people posting '05 MPG's compared to the earlier LLY's.

Just a thought...


Thanks. I see lots of folks are not happy with the LLY and wish they had their LB7's back. On paper the LLY looks like the better motor if not for all the emissions crap. I only drove one LB7...a friend's 2002 with about 70,000 miles on it. The only thing I remember about it was that it was very loud compared to my LLY. Only drove it for a couple of miles with the wife trying to convince her to let me buy one. http://dieselplace.com/forum/smileys/smiley4.gif So far, I'm happy with mine but I haven't experienced any of the problems (tick, knock, surge, poor milage, overheating, etc.) that others have with theirs.

I'm new to this forum, but have had my '04 LLY since July. I tow a Cougar 5th wheel that weighs about 7800 lbs. So far, my best towing mpg has been about 12.5, and that's a bit less than I was hoping to get when I bought the truck. Running empty, I averaged almost exactly 20 mpg on a trip from upstate NY to Roanoke VA and back. That was almost totally interstate driving with the cruise set at 70 mph. Again, a bit less than I was expecting, but not bad compared to what some owners are reporting. The truck has about 6000 miles on it now, so maybe it will improve with time http://www.dieselplace.com/forum/smileys/smiley1.gif. Other than the mediocre fuel mileage, the truck has been great.

A friend and I have identical trucks. Both CC/SWB/4wd. His is an early 2003 LB7, mine a late 04 LLY. His has 20K miles, mine 3K miles. We pull almost identical bike trailers. 7x14 enclosed dual axle pace trailers. (not exactly areo dynamic with the flat front) Mine has "living quarters" so it is about 1000 lbs heavier.


So far, we both get within 1mpg of each other towing, in town, and empty on the highway. His is slightly better than mine, but he is also a more conservative driver. both between 13-14mpg towing, (most of the towing is over the cascades or oregon coast range, half of the trip is hills) 14-15 in town, and and 18-19 on the highway.


At least in our cases, there isn't much difference in mileage. Without one of us driving both vehicles under the same condition, the differnce could be driver rather than vehicle.


Also, another friend has the same trailer as I, with a 7.3L powerstroke. going to california and back from portland, he averages a consistent 13.5 mpg. pretty simlar to both of us.

Why is my 2004.5 LLY so hard on fuel compared to my 2003 LB7?


I'm actually scared to calculate it because I know it is around 10mpg towing my 8000lbs camper. http://www.dieselplace.com/forum/smileys/Confused.gif


It uses almost 50% more fuel as my old LB7 http://www.dieselplace.com/forum/smileys/Confused.gif


Any theorys? Cat? EGR? Turbo?





Have you thought about comparing your mileage with a GPS? I did this to verify my new 2005. I was surprised to see a .3 mile variance over 400 miles travelled. That is much better than I thought it would be.


Plus, I know I get at least 1.5 mpgs more with silver metallic birch. That's why I choose that color!!


Are your REVOS stock size? If you traded "UP" that could definitely change your mileage calculations.


I would start with the GPS on a long mostly straight trip. Your best bet to determine any variances.

I'm new to this forum, but have had my '04 LLY since July. I tow a Cougar 5th wheel that weighs about 7800 lbs. So far, my best towing mpg has been about 12.5, and that's a bit less than I was hoping to get when I bought the truck. Running empty, I averaged almost exactly 20 mpg on a trip from upstate NY to Roanoke VA and back. That was almost totally interstate driving with the cruise set at 70 mph. Again, a bit less than I was expecting, but not bad compared to what some owners are reporting. The truck has about 6000 miles on it now, so maybe it will improve with time http://www.dieselplace.com/forum/smileys/smiley1.gif. Other than the mediocre fuel mileage, the truck has been great.


MEDIOCRE FUEL MILEAGE? I would kill for that kind of mileage.

For the first few months after I had bought my truck I was at about 15
mpg, all city driving. Now its a little over 13, 13.5.
Nothing at all has changed, same drive, fuel up at the same
place. Not sure why that has happened. Driving the highway
i am getting around 16 mpg. Any thoughts or ideas?

Jesse

I started out in the 15-16 mpg range for highway @ 70 mph with my bone stock '04.5 Crew Cab D/A. First oil change it bumped to 17-18 mpg. At 10000 miles I drained everything that held lube (engine, tranny, pumpkins, transfer case) and refilled with fresh. Now I'm in the 19-20 range. Every once-in-a-tank I'll see 21 mpg. Towing my 6500lb boat mpg has gone from 11-12 to 15-16 mpg. <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

I do 70 miles a day, 60 of it on the highway @ 70mph and thats what I have calculated my unloaded numbers from. Most of my boat tows are only 200-300 miles so I'm a little less confident in the accuracy of those numbers. I buy all of my fuel from two stations (one near home, one near work) and run a tank treated with dieselkleen about every three.

I've got about 14000 on it now and I don't expect to see much more improvement so I'll be happily surprised if I do. It sure beats the crap out of the mileage I got with my old 1/2 ton with 350 gas motor.

http://www.dieselplace.com/forum/smileys/hihi.gifWe are in an era of high perfomance diesels. The equation : More horsepower equals more fuel. More fuel means more pollution. The Feds. solution is higher diesel prices and stricter emissions standards. Does EGR ring a bell? You have the solutions but it will come at a high price. Up to $10,000 in fines to the shops that do the work. No information available if you do it yourself.

<DIV>I have a 04.5 CC,D/A,3500 and tow a 15,000 pound Excel fifth wheel . Two weeks ago we went to Denver from Fremont Ne. and both ways I got 10 mpg (from the DIC).</DIV>
<DIV>Last weekend we went about 600 round trip with the same set up and got the same.</DIV>
<DIV>I only have 5k on the clock---I'd kill for even 12 mpg.LOL</DIV>
<DIV> </DIV>
<DIV>FWIW </DIV>

I must not excpect as much as the rest of you. I pull a 30ft 5th wheel and 21 foot boat, that together weighs in around 14K. My 99 chevy 6.0 gas got a steady 6mpg pulling.


the 02 8.1 gas got between 6.5 and 7mpg pulling.


My first real pull with the 04.5 LLY will be this weekend and I will be very happy if I get 10.5mpg. I'll post when I get back from the lake in a week.

I am going to put this out there, take it for what its worth. In August I did a some what MPG test with my truck. I drove 240 miles round trip on the frwy. Filled up before and after and got a hand calculated 20.2 mpg. Now this was in upper 90 to lower 100 temperatures outside with the a/c on the entire time. Cruise was set at 70 mph for the entire trip as traffic would allow. Truck was totally stock. Fast forward to last night made this exact same trip and got a hand calculated 19.2 mpg. Temperature was from the mid 50 to about 70. No a/c the entire trip. Truck now has a mbrp cat back exhaust and edge/*** set at level 1 for the entire trip. Anyone care to speculate why it got worse. It seemed that all factors were in place to make it better. Thanks for any and all comments.http://www.dieselplace.com/forum/smileys/smiley5.gif

OK, let me add my 2 cents.

I went for a 2000 mile drive recently and paid attention to mileage.
Plus I have some background info.

2004.5 LLY CC LB with Lance 1071 camper, SRW with Rickson 19.5 @ 100
PSI, about 12,300 lbs on 4 wheels; LOTS of drag.

We were in a hurry going out, so I set the cruise on 75 and turned on
the AC. Grounspeed in the 80mph range across CA, Nevada, AZ and
Utah. Miserable mileage, about 7 mpg, but got there on time. Lots of
this driving was flat-out WOT stuff.

Coming back across different roads I slowed way down, to the high 50s,
perhaps 60. Mileage doubled!

Here is my take. We all know best economy comes by driving at torque
peak, so that is about 56 mpg in 5th on the Allison. Economy drops off
radiacally off torque peak. Although the V V turbo flattens out the torque
peak, it seems to ENHANCE the drop off in fuel economy. This makes
some sense, but this post is too long already.

Drive at torque peak in top gear in TH mode with the cruise on, even with
a large load. Turn off AC. Run narrow, hard tires fully inflated. You will
get good mileage.

So here is the other part of the story. The reason the Allison is going to
be upgraded to a 6 speed is so we can drive at higher speed, and STILL BE
AT TORQUE PEAK for better fuel economy at today's highway speeds. Also
with the 6 speed a 4.10 ratio rear end is a reasonable option. (4.10 on a
5-speed Allison would get you 5 mpg at 75 mph.) That is my guess, but
a good one.