2006 Dodge Ram 3500 5.9 Cummins Rollin Smoke

[ReubenT]

I am 1 year new to owning a diesel truck. Early last year I bought a 2006 Ram 3500 4X4 long bed with the 5.9 6 speed manual transmission with 285/70-17s on it. The engine has been rebuilt and has about 50k on it now; the truck has over 200k on it. It had 60hp injectors installed during the rebuild; I believe that is the right terminology. It also has an EGT gauge installed on the turbine inlet side. Not knowing a whole lot about diesel trucks I assumed that most people were getting great MPG out of them, in excess 21. When I test drove the truck the fuel economy gauge indicated 22, so I bought the truck with that assumption in mind. I started to do the calculations and it wasn’t even close. I am getting about 14 driving 15 miles back and forth to work, about 16 open road truck unloaded and about 10 when hauling my 7k GVW tongue pull RV, I rarely haul it with water and doubt I am close to the max weight. When pulling a hill I also notice the EGT temp climbs fairly quickly and I have to back off. On some of these climbs I am thinking that the truck should pull up without needing to back off. I try to not exceed 1000, 1200 is my limit. Also when just driving normally this truck smokes heavily when going through the gears, it passes Nevada smog with no problems. I usually try to maintain 2000 RPM. My biggest concern is the smoke, I do not like that it smokes like it does. I can live with the MPG but if I could get that to increase that would be great. It did come with a BD Diesel Performance programmer, I mostly run it on the “Stock” setting; I have run it on the “Tow” and “Stock” setting when hauling the trailer didn’t seem to make any difference.  So I am thinking that I have a few options, install stock injectors, replace the injector nozzles, or if a programmer exists, get a programmer that will reduce the fuel consumption. I would just like to get some thoughts on my “Rollin Smoke” truck.   

[Moses Ludel]

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.

See the popular forum topic on fuel efficiency with the Cummins 5.9L engine.  We cover a lot of ground there.  (I will copy your question and this answer there.)  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 a specific number of miles, begin with a full tank of fuel and refill at the end.

Moses 

Edited January 8, 2016 by Moses Ludel