Well I hate to beat a dead horse but my fuel mileage dilema continues. I have 3700 miles on my 2500 HD 4 x 4 lly now and my mileage is still in the toilet. Averaging 14.1 mpg driving on flat land in Phz AZ with an empty truck. Wait it gets worse I drove up north this past weekend towing less than 1900 pounds and got 10.3 mpg. I really can't believe how bad the mileage is with this truck. I have it at the dealer now and they are checking it out. As of today the are saying the computer shows my mileage as acceptable. I get 17 - 19 mpg with my 7.3 litre Ford consistantly and the main reason I went to the D-max was I heard they got better mileage than the Ford. At this point the same mileage would be a beautiful thing. I'm making myself sick over this and am wondering if I should to take this issue up with GM and if they would support me. I am not a happy camper and at this point wish I would have bought a gasser or another Ford. If theres anybody else having this problem and can suggest what to do I'm all ears.

We are in the same area and are getting about the very same millage. You really can't compare the LLY with the 7.3 PSD, the LLY is a much higher output motor. Let me know if you ever figure anything out. I hear the ERG disconnect helps out.http://www.dieselplace.com/forum/smileys/Ermm.gif


DAN

emmissions.......... that's the word you're looking for.


7.3 motor does not meet "any" regualtions and the LLY meets all. Useing fuel too cool off the thing is basicly what's happening. No3 or your Oxied gasses are the problem........ we are all ahving about the same problem. Run over to a Dodge boad and see what those guys are saying about their new injection system and the fuel mileage they are getting........same story.

There is a difference in the way Cummins uses the Bosch Common Rail and the way Dmax does. When Dmax tackled emissions their decision was to go with cooled egr to reduce NOX. Inducing exhaust gases into the combustion stream has an effect on fuel economy.

Cummins went with what the industry calls "In Cylinder" which means they used all their engineering know how to design a cumbustion process and fuel system to reduce emissions without external means... as much as they could. A smaller turbo was part of the equation.

This also uses more fuel because they add a third injection "after" the power detonation for emissions. What it does I'm not sure... either continues a burn that cleans the exhaust or it actually cools the exhaust? Not sure. They claim high heat creates NOX so that's why I guess the cooling aspect.

Either way you look at it, cleaner engines is costing the consumer money in the purchase and operation of these great engines.

My engine is the pre-600 series (555). It was Cummins first stage of In Cylinder emissions technology using Common Rail. I do not have the third injection or a CAT or any form of egr. Looks like the 600 gets a mile or two less on the average although some are reporting similar mileage as me. 14/20Edited by: hoot

So is there anything else we can do? I already unhooked the egr and I am planning on getting rid of the cat and putting different exhaust on. Is a power box like the edge juice or tts tow tune going to make any difference? Or am I just still going to be sitting here wishing I should have got one of the LB7's avaliable when I opted for the LLY. OR worse yet wishing I just would have kept the old 7.3 furd I had.

Actually the first thing you need to do is be sure it's giving you the same mileage... roughly as everyone else is getting with the same truck. Take into account your driving style too. If yours is drastically less than the masses, you should have it serviced... checked out for a problem.

But it needs to be stock... totally or they will wave you off, blaming what you did on the issue. Tires, exhaust, egr disconnected.. the types of things that can effect mileage.

could be it's a localized fuel issue? maybe we should start a thread on:


Fuel, total miles, cab/bed style , tires, location and milage..


I use Citgo and Sunoco only.. 7K mi on the truck, I Average 18-21 mpg running unloaded.. lowest unloaded was 14 and change, on first tank.


2004 - lly, ext cab, short bed, stock tires.. I'm in MA.

I have a little over 9000 miles on my crew cab short wheel base 4x4 LLY. It has 285/75 R16 on and go to college in lubbock, but during the summer live in a town around San Antonio, TX. I'm getting around 15.5-16.3 in town, and 17.9-19.6 on the Hwy.

Ok, this doesn't need to turn into another one of those miles per gallon threads. I think we need to focus on how we can get better milage out of our trucks. Codythom, How fast are you driving when you're getting 21 mpg? I can slow down to 65 and not see that. Does the wind blow in Texas. In South Dakota we have wind that we have to contend with every day. Now when the wind is at my back I might see 21 at 70 but that's the only time. Going into the wind the milage is just plain sh*t. There is so many variables that affect fuel milage. But speed is a huge one. I really question if some of these guys are getting over 20 with the lly.

It also seems like these newer "emissions" diesels are very sensitive to the current situation. I found that once I get on the highway and reset my AFE (Average Fuel Economy) when I'm at speed... it gives me a true reading of that "situation". If I reset it from cold start, it factors in all that low mileage acceleration and warm up mpg.

I think what is happening is around town mileage suffers more than highway mileage from these emissions changes. When it's all averaged in you get not so good average fuel economy.

If you make long trips you should be getting 17 and up and be satisfied. I get 19-20 not towing but vacation loaded in my Dodge. But my around town stinks at 13-14.Edited by: hoot

Big Rack, you took the words out of my mouth except I would have added a few more cuss words. I get worse mileage than you, but I do have 285's on. Last time I hauled my boat to Powell I was getting 8 MPG, the fan ran the whole time and I was pushing the motor just as hard as I did my V-10. I could have kept my V-10 F-350 and gotten 10 mpg and pulled it just as well. I took mine to the dealer after that trip and they said nothing was wrong. I am very dissapointed and upset. The truck is nicer, but all the tout about the Duramax is overrated. So basically I paid $10,000 more for a 3 year newer, nicer, more refined truck that does the same thing as my old one with worse mileage. Go figure. And I have the rough idle issue! Thanks for letting me rant. I still love the truck.

I get 17 - 19 mpg with my 7.3 litre Ford consistantly and the main reason I went to the D-max was I heard they got better mileage than the Ford. At this point the same mileage would be a beautiful thing.

You have to be careful about things you "hear". Most Dmaxes have been getting 15-18 average with 19+ on the highway. Not necessarilly better or much better than a good running 7.3.

Now where the heck is Broker? Mileage and hauling go hand in hand. He should have gobs of mileage info due to the fact he runs old and new Dmaxes... Edited by: hoot

Good point hoot. It would also be good to hear how GM techs diagnose poor mileage.

For what it's worth I put a Quadzilla tuner on level 1 on customers stock dmax/alli cc dually. He pulled a 30 some odd foot 4 horse trailer with living quarters to Colorodo and got 16.5-17 hand calculated mpg. He was thrilled to say the least.

Yeah the wind blows in lubbock. We have winds that reach up to 60 mph. They are always blowing though. What might be helping me is that in lubbock, it is all flat, not many hills. I don't get 21 mpg, the best I have ever gotten is 19.6. I just don't let it get over 2000 RPM, which is around 70. Taking the muffler and cat off along with unplugging the egr, seemed to help me. The bullydog programmer made a difference too.

I also live in Phoenix and have a new 3500 cc dually lly. Last weekend went to Payson and got 15 mpg average for both direstions. Although I was empty I ran hard up the hills just to see how it would do. 2800 miles on the truck.

I'm gona check thru all our records on the LLY and see how it stacks up against the old trucks.We keep real time records also.The LLY has been flawless so far for us.

Yeah its so funny how sensitive these trucks are to speed/rpm. It makes so much of a difference in mpg. I guess if I was looking for mileage I wouldnt have bought the SuncoastIII.http://www.dieselplace.com/forum/smileys/HiHi.gif

We ran my 01 and my 04 on the same trip, loaded the same. the 01 got 25% better fuel mileage. I have heard that all the newer diesels are fighting the emmisions bugs.

My 2500 HD 4x4 on 315 tires now w/3000mi. on it avg 15.1 mpg on a 1200 mi camping vacation loaded w/camping gear and no trailer. Lots of I-5 @70 to 80 mph. My brothers http://www.dieselplace.com/forum/smileys/Throw Up.gif' 02' F--- F350 on 285 tires powerstroke got 12.5mpg on the same trip filling w/me and hand checking our mileage together, although he had a pop-up camper on his truck so I did expect his mpg to be worse. "I Hoped".


Best I've ever been able to get has been 17.6 @ 55-60 driving it like my mom would on flat HWY 126 to Ventura & back. Seems that anything above that it just gets worse. I'd say about 16mpg on the fwy empty @ 65-70 seems about the norm for me and about 12.5mpg city driving here in Saugus.http://www.dieselplace.com/forum/smileys/HiHi.gif


My mileage is not what I expected reading about all the guys posting 18-19mpg. But still not bad for a big heavy truck. It beats my old 2wd '92' 454 dually on the same camping trip by 2mpg easy and more power TOO!!! Edited by: h8s4ds

3100 miles on 2500HD CC DIC says 16.5 mpg overall, 50% freeway, 30% city and 20% mountain roads (< 60 mph). Couldn't be happier.