Crappy fuel economy? What gives?

[BBowers]

I am the mostly happy owner of a 2005 3500 dually 4x4 with the 48RE auto, 3:73 axles, triple dog programmer from bully dog set on their fuel economy recommended "performance" setting, no cat, trueflow foam element, powerspecialties fuel additive/cetane booster, mobil diesel fuel, marvel mystery oil. I use Delvac oil, and the truck has 18,000 miles on it. This is a great rig and has plenty of power available, but on flat ground in north Florida, no wind, no load or trailer, and 60 psi tire pressure all around, I get a max of 17 mpg keeping it below 62 mph. i even have a slatted fifth wheel tail gate! i saw 18. 2 mpg at 60 mph once on a ruler straight road 36 miles long round trip once that had the citgo station right on the highway, just turned onto the road, put er on 60 cruise control, came back to the same pump, and topped off exactly the same wayand then hand calculated. 18. 22 mpg!! Dad has a 96 4x2 3500 that won't shift into OD but once in a while and he gets 19 mpg with 3:54 gears, auto, and max 60 mph. We both drive like a scared granny with the fuel prices so high. With all the mods I picked up about 1. 5 to 2 mpg by the way, the foam air filter accounts for about . 4 mpg according to the computer by itself. With just the air filter form florida to Chicago running a max of 75 mph and lots of 70-72 mph, I got 14. 6 mpg going up, and about 15. 2 coming back. I need suggestions, maybe i need a different programmer? New muffler? On the tow/economy setting recently and a max of 62 mph, i got 15mpg with 45 minutes of city driving thrown in with a 250 mile rural hwy trip. ALways I featherfoot it!

 

[bpenrod]

Tow something heavy and get it broken in and it may pick up some!!

 

[Bertram65]

Tow something heavy and get it broken in and it may pick up some!!

I have seen this stated quite a bit, what on the drivetrain is not broken in that is going to be after towing heavy? And how can it be causing lower mileage until it is "broken in"? The mileage has been the same on my truck since I got it and I have 34k miles on it now.

Mileage stated above seems normal for an auto dually 4X4. You cannot compare it to previous generation trucks as they were lighter, lower horspower, and do meet the same emmisions requirements.

 

[bpenrod]

I'm just going by past experience with my 03 and my 99. Both of my trucks got better mileage as they broke in. I think my 99 owners manual even recommended towing during the break in period. Either way my mpg's on both trucks went up after long tows with heavy trailers or campers. Both of these ar SRW trucks so not sure how much mpg the dually rear ends costs you.

 

[steved]

I'm just going by past experience with my 03 and my 99. Both of my trucks got better mileage as they broke in. I think my 99 owners manual even recommended towing during the break in period. Either way my mpg's on both trucks went up after long tows with heavy trailers or campers. Both of these ar SRW trucks so not sure how much mpg the dually rear ends costs you.

I agree... my 99 didn't "break in" until I towed 5k for about 350 miles... my mileage went up 2 mpg from that point on. I forced the break in at 50k... they don't break in as soon as you think.



I have yet to hook the 04. 5 to anything that heavy... might just hook the trailer up and get a load of gravel to do it this time.



My 04. 5 gets me around 18mpg average... I can get 20-21 mpg driving like I'm old . And that is with 4. 10s and a stick (which I believe helps some).



steved

 

[Msilbernagel]

Ditto here, 04. 5 w/NV5600 6-speed and 4. 10s. Only difference is mine is in a 93 Suburban... but the mileage is identical. It's had the mileage TSB flash too.



Since you have dually's - I've heard they cost you 1-2 mpg. Does that account for the difference you're seeing?



Mark

-

... My 04. 5 gets me around 18mpg average... I can get 20-21 mpg driving like I'm old . And that is with 4. 10s and a stick (which I believe helps some). steved

 

[steved]

Another thing to consider is the fact that these truck have gotten heavier... and the fact that a comparable gasser is most likely in the low teens and probably single digits when towing. And to make the power they are today, takes fuel.



I don't see where two extra tires would cause that much drag, but...





steved

 

[Sled Dog]

I am the mostly happy owner of a 2005 3500 dually 4x4 with the 48RE auto, 3:73 axles, triple dog programmer from bully dog set on their fuel economy recommended "performance" setting, no cat, trueflow foam element, powerspecialties fuel additive/cetane booster, mobil diesel fuel, marvel mystery oil. I use Delvac oil, and the truck has 18,000 miles on it. This is a great rig and has plenty of power available, but on flat ground in north Florida, no wind, no load or trailer, and 60 psi tire pressure all around, I get a max of 17 mpg keeping it below 62 mph. i even have a slatted fifth wheel tail gate! i saw 18. 2 mpg at 60 mph once on a ruler straight road 36 miles long round trip once that had the citgo station right on the highway, just turned onto the road, put er on 60 cruise control, came back to the same pump, and topped off exactly the same wayand then hand calculated. 18. 22 mpg!! Dad has a 96 4x2 3500 that won't shift into OD but once in a while and he gets 19 mpg with 3:54 gears, auto, and max 60 mph. We both drive like a scared granny with the fuel prices so high. With all the mods I picked up about 1. 5 to 2 mpg by the way, the foam air filter accounts for about . 4 mpg according to the computer by itself. With just the air filter form florida to Chicago running a max of 75 mph and lots of 70-72 mph, I got 14. 6 mpg going up, and about 15. 2 coming back. I need suggestions, maybe i need a different programmer? New muffler? On the tow/economy setting recently and a max of 62 mph, i got 15mpg with 45 minutes of city driving thrown in with a 250 mile rural hwy trip. ALways I featherfoot it!

Thats what I get with SRW 1 ton. Your making me wish I got the duelie now.

Try advancing your timing 2 degrees with Rokktech crank sensor, I picked up 1 to 1. 5 mpgs.



Towing did not increase my mpgs on my 05. I hooked a trailer to mine at the dealer when I bought it and towed a ford 360 miles to the house at 80+.

 

[BHolm]

My experience with towing to get the engine broken in is a little different. My '03 QC now has almost 80k miles on it. Back when it had 20-30k and had already done a bunch of max load pulls I could coax 18-20mpg out of it. Now after 80k miles and LOTS of 15k lb loads I get about 22 mpg cruising at 65-70. The truck has amazing power, seems better than my 30k mile '05 for sure. I was looking to trade it on a mega cab and the dealer guys couldn't believe it didn't have a fueling box. It is strong and efficient. My theory is that most of us have a hard time REALLY building up the cylinder pressure the way the engine requires to seat the rings. I honstely think that you need to do 10k miles of really heavy pulling to get where the Cummins is broken in. You have to run em hard, like any engine, to make them fast. Considering the CTD is overkill in a pick-up it is no wonder they take so long to get broken in, most guys don't work them nearly hard enough.

 

[DPKetchum]

Every vehicle I have EVER owned got better milage with miles on it. My 03 has improved a great deal since new. Intown/two lane blacktop etc. was in the 13/14 mpg range tops. Now its 16 or better(right NOW overhead shows 17. 2. Hiway was 15 or so. Now its in the 17 plus. Have 20k on mine now. Just towed 9k(horse trailer and 2 horses)to South Ga. very mixed driving. stop and go through atlanta,twisty two lane,rural hunting a address etc. hand figured was 13. 7. I was like WOW. My 93 Dodge with Cummins and a fair amount of mods was in the 11 range.

 

[Sled Dog]

When they went from the 555 HO to 600 and 610. It should read 600 HI and 610 HI,

HI for high input of Fuel.

 

[Gray 5.9]

I have 60,000 plus miles on my truck and the best Ive seen yeat is 17. And is doesn't matter if I do 60 Mph or 80 thats all I can get out of it empty.



Could it be tha

t I might have to tow a heavy load for a fair amount of time to get this engine to it's max MPG? I'm already running a true flow air filter that made a noticable diffrence in sound and a little more peppy, and a Rokktech sensor.

 

[testraub]

Not to be too smart or anything, but I just stopped used the SP Diesel Elminator box on my '05 and am now beta testing (again) their newest box. Just going by the overhead. 14. 1 MPG on the old 16. 5 on the new City driving. For the first time, just after the install at Fall Brawl on the way home I got 20. 7 MPG on High Output (HO Mode) and I'll swear thats the highest I've ever seen on the overhead. Now remember, this is the first tank of fuel with the new box, and I haven't had time to hand cacl everything, but it sure looks good from here. SP Diesel ( http://www.spdiesel.com/ ) is really working on things our trucks are looking for. Heck They even solved my old P0111 code problem and allowed me to start using my CB Amp again. I'm a BETA tester for them am I'm really looking forward to what they plan to give me and the production boxes. (BTW Just between you, me and the fence post, They have several features you will NOT find elsewhere. )

 

[jimnance]

I've got a similar rig to your. I'm getting right around 16 MPG and driving her like granny. 65 MPH on the highway, and gentle around town.



I agree with most of whats been said above. Advancing the timing should help, but I think you need to consider that you've got a vehicle that is much heavier than earlier models and you have more drag with duals than an SRW.



I haven't seen much improvement in any of my earlier CTD's after break in. If it was there it was a modest improvement at best. My '99 has 100K with a fair bit of it towing 12-14K. I can't honestly say it gets any better mileage now than when it was new. Overall, it gets around 19 MPG combined city/highway. .

 

[MMeier]

Thats about right, these new fangled things just will not get the mileage the older trucks did/ do. 97k on mine now and mileage has never been anything to write home about! :{ My old 97 would get 20 plus empty regardless of how I thrashed on it, worst was 11. 5 towing 28k# up in the Northwest one trip!

 

[MMcdonough]

My 2005 2500 4x4 auto 3. 73 truck is hovering right around 18 mpg with a mix of highway and city. That's with about 8800 miles showing. I'm pretty happy as this mileage is just over the average I saw out of my last truck (97 Ford F250 PSD 5spd with mild mods).

 

[JCotte]

When they went from the 555 HO to 600 and 610. It should read 600 HI and 610 HI,

HI for high input of Fuel.

I guess some people need an education that it takes more fuel to make more power. Here is the Formula Torque X HP = Fuel$$$$$$$$$

Seriously, the Rokktech sensor does the best improvement that you can make to fuel on a STOCK truck. YES fueling/timing boxes do help a bit (mostley because of the timing) but in general it does take more fuel to develop more power. Seeing how i am just about 20. 5MPG :-laf with my Rokktech installed i am not about to complain. i was at 18. 2 before i installed the sensor.

 

[BBowers]

Well, look here, I don't happen to have HP and torque curve in front of me for the 600 Cummins, Mr. Thinks Everyone Else needs Eddycation, but I do know that computer controlled diesels in every other market segment have made enormous gains in fuel economy over mechanical injection. Computer controlled diesels have done for trucks what EFI did for cars, more torque, better responsiveness, lower emissions, and more scientific controllability of any variable regarding timing of fuel delivery, spark(on gas), etc. Most importantly, better fuel economy!! My old 1972 mustang mach 1 had a 351 cleveland and made 164 horses, maybe 180 with exhaust. It had around 300 lb ft of torque I would guess. I got 16 mpg hwy at 65 mph with 2. 75 rearend and a C-6 auto,2 barrel, full exhaust with long tubes, 12 around town babying it, and 93 octane. MY 1991 302 mustang with EFI and 3. 08 gear and manual shift 5 spd made around 240 horses with mufflers, air filter, and 93 octane got 25 mpg 19 city thrashing on it (hwy at 75-80 mph) and weighed close to the same. Go figure. I know an overdrive helped, but the 1972 had a 2. 75 rearend ratio. EFI rules!! Not to mention it would blow the doors off of the 1972. Enough said. So, the computer controlled engines should have a nice balance of economy AND power. So, there you have it. There is no reason why the computer cant back off on pulse width and advance timing at cruise with no load and get enormous mileage gains. It only takes around 50 horses I'd guess to keep a ram pushing wind at 80 mph. A mustang takes only about 15 horses at 55 mph in still air. Even if my numbers are way off, it should take no more fuel to keep my rig rolling at 70 than dad's 96 with no load, except for slight increase in curb weight. He gets 22!

 

[jimnance]

In general this has been true. However, the big three engine makers, Caterpiller, Detroit, and Cummins had to comply with the 2004 Nox emissions early as a result of getting caught cheating by the Feds on emissions standards.



I can tell you that the "new" engines in class 8 trucks that had to meet the new emissions requirements were gobbling 10 to 15% more fuel than the pre-Nox engines. I happen to be in the trucking business, and we aren't too happy about it!



So, you can't compare apples (gas engines) with oranges (diesels). The new Nox emissions standards have been very difficult for the engine manufacturers to meet. Diesels, by their nature have very high ICP's and combustion heat. These are the conditions under which Nox is formed most readily.



I've heard talk that when ULSD is fully implemented they may be able to scrub some of the Nox with a catalyst. I'm not certain if this is true, but if it is it would be welcome news to the trucking industry which is already laboring under the pressure of high fuel prices.

 

[DPKetchum]

The EFI thing in diesels is still in its infancy. Some of the SAME problems I heard and experianced in the mid 70s to 80s with EFI on gas burners is the SAME I'm reading now in diesels.