[Driving Your Dodge Ram Cummins for Fuel Efficiency!]

Hi Ludel I have a 2006 Dodge Ram 2500 4X4 5.9L. My truck has 3:73 gears and 35 Toyo M/T 2 " level kit. I drove to Macon Ga. from Tampa Fl.@ 65mph and got 28 Mpg up I75 in March of this year. I am lifting my truck 6" and putting 37" Toyo MT on. I was going to put 4:30 Nitro Gears in. I also got 25-26 MPG from here to NC in Dec. of 2014. My MPG around town is 16-18 city driving. Now all of this is empty truck bed. Now i do plan on towing a camper to Ga every now and then and any where else i go for vacation. I was wondering being that my RPM's are around 1600 to 1700 at the speed mentioned above would i receive equal results  doing my lift and gear change. I used a RPM calculator and for the given size tire the rpm's for a 4:10 set up were 1829 rpm and for a 4:30 set up 1913 rpm. Now i compared that to the set up I have now using the Calc. and my rpms are 100 rpm higher with the 4:30 set up and lower with the 4:10 set up than i currently have. I think you are reporting that the 5.9L sweet spot for fuel maximizing is around 2000 rpm, because you want the higher rpm range when traveling at 70 mph + to avoid high boost pressures. 

  Oh my calculations were done at 70 mph.  If I go to a 4:56 set up the rpm's go over 2000. Can you help. with a bit of knowledge.

[Driving Your Dodge Ram Cummins for Fuel Efficiency!]

On 1/8/2016 at 9:38 AM, Moses Ludel said:

RuebenT...Considering all of the features and mods on the truck and engine, the injectors must be the issue.  The BD programmer or even the stock ECM would want to pulse the injectors at the stock injector flow rate.  The high output injectors would be pouring more fuel per each pulse of the injectors.  The poor fuel mileage and black smoke reflect this during your run-up through the gears.

I would also suggest that 2000 rpm is a bit high for maximum fuel efficiency, though 14 mpg would not be the result of your 2000 rpm shift points or cruise rpm.  For maximum fuel efficiency with the 6-speed's gear spacing, I would upshift at 1250-1400 rpm with no load and 1600-1700 rpm with the trailer in tow.  Note the mileage increase.  

This engine has a prompt torque rise and makes peak torque (stock) by 1600 rpm.  Especially with the six-speed transmission, running between 1600 and 1900 rpm at flat ground cruise speeds in overdrive, your truck should achieve at least 19-21 mpg running empty.  Your trailer load is not excessive for the 5.9L Cummins engine, towing should get 14-17 mpg.

Gearing would be another concern if you were running greatly oversized tires.  You're not.  If you have stock axle gearing of 3.73 or 4.10 ratio with the 285/70x17 tires, 20-plus mpg should be attainable without a load.

One thing for sure, the factory mpg calculator is way off, and that's typical.   Like you, I find that the only way to clearly know mileage is to run an accurate and specific number of miles (known road distance); begin with a full tank of fuel and refill at the end.  Calculate your mileage from there.

Moses