Horrible Fuel Mileage

[BHolm]

Thanks to all you guys posting!! I really appreciate it. I will check my mileage again maybe after towing a buddy's car trailer. Also what tire pressures do you guys run, I only have D-rated tires and I run like 45psi in the front and like 37psi in the back (truck is never loaded). Thanks again, all of you are very helpful.

If you are towing a significant amount of wieght, I would inflate the tires to the max on the sidewall, should be 65 psi, I would probably bump the fronts to 50 psi.



Get as much wieght behind it as you safely can, find some long grades to pull and don't baby it! I have pulled a 28' enclosed into the wind making 30 psi of boost for several hours. It sure goes through the fuel but the return in empty milage later was worth it.

 

[RonVpr]

I have a 04 QC 4X4 long bed 6 sp. My mpg was a constant 18 doing mostly freeway. After install of a Banks High Ram intake and 4" exhaust and Air Raid intake, it went to 20. 5 to 21. Now with a Spearco intercooler, and keeping it at 67 mph on the x-way my, 80 mile daily commute is getting me 23mpg. My old 98 could only muster about 20 with the same mods. I now have about 100k miles on it. I will say this though, after about 30k my mileadge improved about 2mpg. I would have it checked at a dealer.

 

[Lifted Mega]

bzeig don't hold your breath as for the mpg. I'm in the same boat as you but i have worked mine and still no increase from day 1. I'm at a loss so is the 2 dealer shops and 2 independent shops. Everyone is still scratching there heads. From day 1 they told me put some miles on it and it will come up. Well 30000 miles later still no increase. This is my 4th cummins, i hate to but i may just sell this SOON. Check my other post under Fuel mileage comparison for more details on my mpg.

 

[betterthanstock]

Never even seen a trailer behind her, just babied, always warmed up before driven, I stay 70 mph on the freeway and just creep through town. Any help or suggestions? Thanks, Bobby

I never warm mine up. I back it out of garage after 5 seconds. Takes me an additional 30-40 seconds to get out of the driveway. Then I moderately accelerate to 50 mph for nearly 2 miles before first stop. It has a diesel rattle for about 5 seconds, then it's quiet.



A cold idling diesel is never good. You don't need to warm it up in California.



Don't just creep through town. The best mileage is at about 45 mph, not 25 (if that's what you mean by creeping).

 

[BHaden]

What they all said; don't warm it up. I start it, idle for 30 secs and drive away gently until warm. Won't hurt it a bit, just keep the revs down for 5 miles or so.

DO tow something somehwere. Mine got , at best 15. 5 on my daily 83 mile/60% highway commute until I towed a 6k trailer 3500 miles. After I got back mileage went to mid 17s and stayed there. Also note mine is a Megacab dually,

so if I can do it you can.

 

[RMarkey]

Good luck man, your in the boat with me, I've towed just about everything, I plug it in and don't let it idle, I put the chip on "mileage" and it just starts smoking slightly after a while of driving around 50-60. I gave up and just accepted the crappy mileage. I'm around 50k mi. It never had good mpg stock and it gets the same mpg bombed, so I figure, what the heck, might as well just drive it and try to ignore the mileage. It still beats driving a pooperduty or a duramax(although better mpg with it).

If you ever figure it out, please let me know. I've thought about doing injectors because those are problematic, maybe fuel pump or fass system, even a dyntrack hub conversion for that . 5 mpg increase, but they're all to expensive to just "try".

 

[SBeretz]

I agree with all the guys about warming them up, I start mine, let the oil pressure come up and then go about 2 miles under 30MPH, by the end of 3 miles, my oil temp is at about 105 degree and from then on I turn on the main road and set the cruise for 55mph.

On another note, they are all dead on about really towing something heavy and letting the truck work. Ever since I have started towing my toyhauler, my mileage has improved up to the 45K mark. Lately it has leveled off and has stayed around the 20mpg mark. . I think you will get it, find something and work it. You will be surprised at how the truck responds to it. Scotty

 

[DLane]

Thanks to all you guys posting!! I really appreciate it. I will check my mileage again maybe after towing a buddy's car trailer. Also what tire pressures do you guys run, I only have D-rated tires and I run like 45psi in the front and like 37psi in the back (truck is never loaded). Thanks again, all of you are very helpful.

Right here is a easy one I am very surprised no one caught. Air up your tires. 80 back 60to 65 front. That alone will get you improvment. It's a truck not a family sedan.

Do not baby it and expect it to last, you want it to run good for a long time work it HARD. A 5 to 6 K trailer is not hard. LOTS of miles towing HEAVY stuff will help. My 05 roughly 18K running empty and 90K pulling 9K plus at 80mph or more. I get 15 and change towing, and hover around 23 empty. At the highway speeds above. Truck has been stock, no program or chips for the last 50k. In the simplest terms abuse it it will work better

 

[STEVEBROOKS]

1. 80035 miles, of which 10776 were towing approx 12K

lbs



2. 24. 64 mpg high (unloaded/65 mph/88 miles)



3. 7. 65 mpg low (towing/65 mph/178 miles/40+ mph

headwind!)



4. 16. 04 mpg overall avg



I couldn't be happier with my truck! VERY few, small problems over the years. Suggest hooking a big load to yours whenever you can, and let 'er roll!



Steve

 

[SilverSage]

I have an 05, 48re, 3. 73 gears that I have had for just over a year. She had 30K when I purchased her (45k now) and usually gets 10-11 mpg in town and 14 mpg unloaded on the highway at 70 MPH and up to 15 mpg at 65 mph (1800 rpm at 65mph) I do not baby her and tow a 4K travel trailer getting 9-12 MPG. I have tried many "moderate" mods but none have helped. She is a great looking truck with a very comfortable ride. I just finished a 4500 mile road trip (Denve to Central Florida) and got an average of 14mpg at speeds of mostly 65 @ 1800 rpms. The millage sucks and nothing can be done about it!! It means that I will travel about 40% less in my retirement than I really wanted to.

 

[betterthanstock]

I have an 05, 48re, 3. 73 gears that I have had for just over a year. She had 30K when I purchased her (45k now) and usually gets 10-11 mpg in town and 14 mpg unloaded on the highway at 70 MPH and up to 15 mpg at 65 mph (1800 rpm at 65mph) I do not baby her and tow a 4K travel trailer getting 9-12 MPG. I have tried many "moderate" mods but none have helped. She is a great looking truck with a very comfortable ride. I just finished a 4500 mile road trip (Denve to Central Florida) and got an average of 14mpg at speeds of mostly 65 @ 1800 rpms. The millage sucks and nothing can be done about it!! It means that I will travel about 40% less in my retirement than I really wanted to.

The 14 mpg was empty, no camper/trailer?



Fuel does not just disappear.

Definately something wrong with injection timing, or cam timing. Is oil staying free of soot or fuel? Is torque converter locking up? Transmission temperature? Brakes are not dragging, and no external fuel leaks at high pressure I assume. I would replace the manifold pressure/temperature sensor, and the intake (on air filter housing) sensor. I think the ECM also has a built-in pressure sensor, for altitude but I am not positive on that one. These sensors being off, can afect injection timing and pressure. Also check the fuel rail pressure sensor, maybe swap with another truck. On a used truck, the previous owner may have messed with the "tone wheel" and retarded timing while trying to advance it. Investigate, and find the cause. Maybe a Cummins shop should be checking all the cam/crank timing, but I would still replace those sensors first, since they don't cost that much at Cummins.

 

[10-9jc]

Thread "revival' here -

Several posters say the same as "SilverSage".
I have the same '05 (except 4:10s),
and get about the same mpg at 33K miles (stock).
I try to drive 65 mph on the hwy (max) due to the 4:10s.

Betterthanstock - you have an '03 (?) -
apparently seem to get better mpg (before any mods) than the later 3rd gens. Of course, stick helps too.
JC

 

[SilverSage]

With regards to BetterThanStock , I have had my truck in at many dealers in the Denver area and had no luck with them finding any problems with the computer or sensors. They all said everything was perfect and 10-15 MPG(unloaded) was great mileage for that truck. The truck came equipped with a BD e-Brake which has a “controller box”. One Dodge dealer said that the controller was a power chip and that caused my problem. The ignorant A-holes at every dealer I have been to will never admit there is a problem with the truck it is always the fault of and caused by the owner/driver. Good news though, I have now driven about 8K miles with a Smarty Jr. in the tow mode and have gotten a 1. 5-2 MPG improvement in mileage. When towing a 4k travel trailer up the Colorado Passes, I was limited to about 60 MPH due to EGT approaching 1300 degrees, now I can drive 65 MPH and EGT don’t get above 1250 degrees. Smarty Jr. is the only mod that has improved my MPGs and with Diesel at $5. 00/gal Smarty is very smart.

 

[SilverSage]

With regards to 10-9jc , I travel with a friend who has an 03 1 ton single rear wheel with an HO engine. He gets 17-18 in town and 20-21 on the highway unloaded. The 03 does not have a cat and has a much different computer than the 05. I would say the 03 trucks get much better MPG if at somewhat lower horsepower and torque without mods.

 

[AMcCormick]

I recently did a cross country trip, Key West FL to Stockton CA. Total miles logged were 3750 using total of 231. 9 gallons averaging 16. 17mpg at a cost of 1107. 25$. This was done towing a double axle 12x8 U-haul trailer stuffed to the gills full of everything we own.

 

[RVTRKN]

I recently did a cross country trip, Key West FL to Stockton CA. Total miles logged were 3750 using total of 231. 9 gallons averaging 16. 17mpg at a cost of 1107. 25$. This was done towing a double axle 12x8 U-haul trailer stuffed to the gills full of everything we own.

I noticed on your sig that you have the dyna-trac system on your front axle. Can that be why your MPG was that good?

 

[Turbo_Bob]

I am new to Cummins Turbo Diesels and I have a bone stock 2004. 5 with the 48re with 3. 73 gears, tires are 285/75-17, only 22k miles on it; and I only get an average of 12 miles per gallon hand calculated!! I stay 70 mph on the freeway

Speed makes a huge difference, I would recommend you slow down from 70 to 65 MPH for a full tank and see what that gets you.

But it sounds to me the engine may need to be reflashed ? As you stated your MPG should be around 19 at 70 MPH.



I have a 2003. 5 HO, 6 speed stick, 2 wheel drive, 1 ton quad cab short bed, 3. 73 R&P, tire PSI unloaded 45 F and 45 R.

At 70 MPH it gets 21 MPG

At 68 MPH it gets 22 MPG

At 65 MPH it gets 24 MPG

Hand calcs ! I allways get over 800 miles on my trip gauge before fillups.



When diesel goes higher #@$%! like in Europe I will be forced to slow down to 60 MPH, might get me up to 26 MPG ?

 

[RVTRKN]

Turbo Bob: 16. 5 MPG towing trailer weighing at (guess) 5K seems to be good MPG to me.

 

[DE Jeeper]

With all my mods and I drive too fast around town I still get 15 mpg. I also scale out at around 8200# with all my tools. I was able to get 21 mpg a couple weeks ago, but I was steady between 55-65 mph. Since power is metered by fuel on a diesel your right foot greatly influences the mpg.

 

[AMcCormick]

I chose to do the free spin kit mainly because the truck spends 98% of its life in 2wheel drive. No need to be spinning extra parts/weight. I did that trip with small stock size tires, I think 265/45. I had two flats within 30 minutes of each other about 5hrs out of KeyWest. After spending the night in front of a Firestone shop I bought 4 new tires. Not exactly what I wanted but didnt have much of a choice. Did the trip with those new 265/45/17 tires. Logged everything based off the overhead trip odometer. I am now running the Toyo MT @35" and they are drastically effecting my mpg. I wanted to run the 285/75/17 size but when you get 4 new tires as a gift you dont say no. I think I will need to find a set of wheels and run the 265s for daily driving. I have not logged any mpg with the 35 yet but am positive they are not helping.