Cummins 6.9L turbo diesel economy
 

Hello, I have a question for you, after reading the hypermiling section I have done very well increasing MPG of my 2014 Ram 2500 from the low 13s to the mid 15s. I've been trying to get more efficiency out of it (what seems reasonable given my typical driving situations), seen all sorts of suggestions for accelerating, and I'm not sure which make sense for my engine. It sounds like quicker acceleration is better than slow, which makes sense to me and playing around with it I see a definite difference going harder on the pedal than grampa, but I'm sure there's a point at which this becomes as bad as or worse than creeping up to speed. Like flooring the pedal to the speed limit then coasting (I got here searching for pulse & glide). The consensus seems to be that my engine sips fuel best at 1600+/- RPM (peak torque according to Cummins), and for me that's between 60-65 on the freeway. So would accelerating trying to keep the tach as close to 1600 while it gears up make sense? I drove a friend's Ram with a driving coach tuner and as I recall it showed where you should be as you accelerate in a red-yellow-green band sort of display, unfortunately I wasn't paying attention to the RPM.

I'm guessing you have such a low RPM at 65 due to large tires? If so, they are probably hurting your MPG. 15 MPG in a Cummins isn't great.

Focusing on acceleration won't give you as much improvement as focusing on rolling resistance, aerodynamics, and avoidance of using the brakes.

I put tall and wide tires on my 5.9L and the MPGs dropped. The front end is not good, especially since the track bar wears out almost instantly. I've had issues with calipers dragging too. On top of all that, my tranny is going. I'm still able to get 20 MPG at 65 on the freeway.

I agree, even my gas Sierra could flirt with 15MPG if I was going ~60MPH.

Do you have any mods done to the truck? Oversized or offroad tires? Lift? Tune?

It's called DPF and regen. That RPM is better then the older ones as that truck has a better transmission. To bad they didn't have the newer 6 speeds with the older, pre-emission 5.9's. That would have been killer.
Anyway, by keeping the EGT's low you improve economy, but then you get an active regen cycle more often which dumps raw fuel to burn off the DPF. Driving it a little harder may keep the DPF clean without regen. What is best for economy I have no idea. Delete the DPF and deactivate regen would definitely help.

I see a youtube video that claims 1112 degrees is where passive regen occurs. It also says if the active regen cycle is started and you turn off the motor before it finishes, it will start all over on the next startup. It is probably not 100% accurate for your application but an interesting video.
https://www.youtube.com/watch?v=aMKpo74P6SE

Some of the rules that apply to gas engines don't apply as well to diesels. Gas engines are most efficient at high throttle (accelerating briskly) in part because closing the throttle plate and generating vacuum robs power and efficiency from the engine. While some do, many diesel engines don't have throttle plates, and a better rule to follow is just to keep RPM down.

You might want to check this thread out:

http://ecomodder.com/forum/showthrea...kup-21766.html

For me and my 1st gen 91.5 I keep the egt about 700-750 to speed then about 500 or less in town and 800 to 65-70mph dr p to 500 flats 600 slight incline 700 about 5%grade 800on 7% with an occasional bump to 900 to accelerate and maintain OD (shift point 59 mph@above 825egt)
no tack so heargos
235/85R16 Revolutions per mile (km)635.65 (394.97)
3.55gear , .69OD =1557rpm @60mph +5% (for no lockup) = 1634 rpm .peek tork 400ft lb @1600
18.xxx avg naked 24.xxxmpg with cap

I have taken a 2012 3500 flatbed with 6.9l geared for towing( i think 3.9 or 4.10 rear end) for an 800 mile trip, and it would hold just under 19 mpg unloaded until i hit a regen, it droped to 18 when it was done. After that i would squeek it back up to 18.5, then back to high 17 on next regen. All said and done i got about 17.5 mpg for that trip.

The regen cycles and towing gears really do kinda kill getting good mpg.

A mid 2000s 2500 with 5.9 I held to 25 to 26 mpg for a 100 mile trip parking lot to parking lot but i dont think that was geared for towing as it held low rpm while cruising at 60 to 65. NO regens on those older trucks.

Beautiful, so I can believe what Cummins has been telling folks (with no actual data or even an explanation). And not to offend anyone but I keep hearing about claims of higher MPG than the factory MPG with no mods or fooling around with the EGR emissions etc. and that might be what a hypermiler gets but you can only piss off so many people on our local roads. And these engines are supposed to be getting less efficient in each gen as the EPA cracks down on MPG. I bought it precisely because it was the last model that didn't require the ridiculous DEF. I'm more curious if anything but saving on guzzle even if it's only $10 a tank adds up. And for the record my truck is 100% stock and the tires are actually an inch smaller because I need an aggressive tread and the factory size tires are $400 more for a set. Also I have a steel canopy that it sure adds weight compared to fiberglass. Right off the dealer floor (almost NOS, I think the guy who sold it back to them kept it in his driveway for the looks) I got 15.7 on a couple hundred mile freeway trip @ 65 on cruise control not even knowing how to drive economically yet. Haven't seen that since so regen could certainly be a factor. I don't do enough freeway miles for it to kick in at a more optimal speed (or so I have been reading). Thanks everybody for your input!

There's no such thing as "factory MPG". I assume you're referring to what EPA testing suggests the typical driver will get?

Hypermiling doesn't have to piss people off, either; it depends on what you're doing. Certainly tailgaiting large trucks and driving 25mph under the speed limit can be annoying, but there are plenty of other safer ways to save fuel. Remember that every time you push the gas pedal down you're burning fuel to gain momentum, and every time you press the brake pedal you're turning forward momentum into brake dust.

An example of a driving habit that can save a ton of fuel but not piss people off is situational awareness. For example if the light ahead of you turns red, don't keep on the gas until the last minute and then slam on the brakes, but instead take your foot off the pedal and take your time getting there. Nobody is leaving the redlight any sooner than anyone else, and by doing this alone you can often beat the EPA city rating by 25-50%.

Weight is far less important than aerodynamics on the highway. Any roof racks or bits you bolt on to the outside are basically small parachutes catching the wind and pulling your truck to slow down.

Your truck may not have the urine injection but it definitely has a DPF and regeneration modes. You need to learn when those are happening and how to limit them, and never interrupt them (or they just immediately start all over again from scratch). That or just get rid of it. The 6.7 can get good mpg even bone stock. TFLtruck has a YouTube video of one doing a empty loop where they get over 20mpg. Then again their Ecodiesel Ram did 33mpg on that loop which is why that's the truck I really want.

Ps, I have a friend with an 2012 and he is only getting 15 but he is going 75. At least he says pulling a horse trailer it only drops to 13. The canopy actually probably hurts aero compared to an open bed or flat cover, steel or fiberglass. The smaller tires also hurt especially with aggressive tread. They increase highway rpm and I bet they are just as wide giving no reduction in frontal aera.

Still, 15 MPG at 65 MPH is not great for a diesel. Is this really what these trucks are getting? I don't think I've ever had a tank get less than 16 MPG.

Still, 15 MPG at 65 MPH is not great for a diesel. Is this really what these trucks are getting? That's the worst MPG I've ever recorded on my truck, and it has a headache rack sitting above the cab, oversized offroad tires, a loose automatic tranny, and a sloppy front end.

Well he said 75mph but the interstate he runs to work on has an 80 mph speed limit and Montana will let you go 5 over all day without a second glance. I bet when it's clear and daylight he is doing at least 75. I also notice I don't see the truck except on the bad weather days pretty much, think cold air, rain or snow, and diesel #2 in the tank. He has a big deer catcher, welded bumper on the front as well after his stock setup caught a deer. I think he feels a little safer with his 120 mile (round trip) commute in the Ram then in his Grand Cherokee, and I don't think he gets much better mpg with the Jeep. He is close to retirement so moved way out in anticipation of only having to do it for a year or so.

15.7 mpg cruise set at 65 dead flat no wind. Never had it go any higher, and that was before the tires and canopy, driving back from the dealer. 15 maybe 15.1 with the canopy and tires. And yes I do try to not use the brakes and time the lights etc. Heck I even ramped up my no stop at a right turn stop sign campaign. Playing around on a boring trip I did 55 to 70 in 5 mph increments, same stretch, 10 miles each. Highest was between 60 and 65, closer to 65. Starting tanking at 70. So how do you control the regen?

From what I read trying to research if I want a 6.7, there are active and passive regens. The truck won't say anything on it's own when it goes into active regen unless the DPF is really full. Basically it only sometimes warns you when you really need to let it finish or risk a 100% full DPF that then won't ever trigger an active regen without a trip to the service center. Other times it just does the active regen when it feels like but unless you have some kind of aftermarket gauge like the Edge, you may not notice. If you stop in the middle, it just restarts next run, again if it doesn't finish, it restarts again. With the EGR and DPF in place I would avoid idle at all costs, that really seems to soot the whole system. The passive regen is just working the truck hard enough that it burns it's own soot, so towing or going up a long hill should give you freebie regens. The DEF system actually helps reduce the number of active regens, so some find better MPG with that system although then you have to buy that crap so they end up paying more.

Personally, I would delete the DPF, deactivate the regen, and turn off the EGR but leave it in place. I would do it even if I were leasing the truck or if it was under warranty, although the trucks I have looked at are all out of warranty anyway, and some have the deletes in place already.

if you want to keep it all stock, an Edge gauge or something similar you could monitor the DPF level and learn when it does active regens. Then next time before it gets that point, a higher speed or a downshift may hurt mpg temporarily, but may get the EGT high enough to get some passive regen going. Then slow back down. If you are going to be adding fuel in a regen, you might as well be using the fuel to go faster ultimately getting better mpg overall.

Install an EGT (ehxsost gas temperature) gage with a "fast response "prob . Then apply target Egt technique similar todriving with a Vacuum gage except yout target is the lowest temperature to maintain speed instead of the highest Vacuum . For my 1st gen cummins its about 500°f on flats 600 Med grade 700f heavy and 800 for major aka 7%and up ,all at 65-60mph (my trans will not hold OD above 800° below 60mph).
Some times on a grade as the rpm drop the EGT will rise 50-100°f with no change in throttle. in theas situations back off the throttle and maintain your EGT set point . I recommend the "fast response " because with my truck the needle moves at the same speed and ratio as my foot.
Just reducing the pressure but not the position will sometimes result in a 25-50°drop and will cause acceleration. Dont understand the physics behind it ,but it works.
I think the region should show up on the EGT gageas well .

Hi,

New here but our delivery truck is a 2014 with the 6.7 cummins and highway we get around 22MPG and 17-19mpg city depending on traffic

its been "fixed" of course though

a lot is in the use as well. running your fuel supplement at all times, cleaning the turbo and intercooler each year.

Best mpg will be at 60-mph or below. The trucks hit a wall at that speed or higher.

For a highway trip under 300-miles, average speed will be close to speedometer set speed if at 60. Faster one goes, the greater the discrepancy between average (actual) and speedo set speed. No lane changes, no braking, no off throttle to deal with traffic, etc.

This is so up to 62-mph. After that one is mixing with commercial traffic

High mpg is long term discipline. Several hundred thousand miles. The diesel fuel advantage takes just about 200k miles to achieve (over gasser equivalent) in a pickup.

15 is what I average with a 35' travel trailer. It's lousy for a solo truck.

And the engine is a 6.7. Only 6.9 was a 1980s Ford with a Cornbinder oil burner.

I wonder if this is the reason for your current mpg? :)

14 MPG seems to be a "real world" consensus for the 6.7L diesel 2500 (not just highway). It's pretty easy to keep 14 with no load and significant highway miles. 17 highway (EPA says I think). Remember this is on a 2012, they're getting better every model year (16 on the 2016). I've never got that high even on short stretches under ideal conditions. Maybe at 100 degrees with a tailwind lol. BTW I've cruised the net and Cummins 67.L should be run at 1500-1600 RPM for best economy. Now if I could only keep that through acceleration up to cruising speed lol.

The technology helps the newer trucks but the emissions equipment offsets the gaines. My 1st gen intercooled5.9L 91 stock ran from 16mpg to 22.5mpg withan avg of 18.xx. With the Aero Tonto my numbers are 21mpg with 2 100mi runs at 29.6mpg from Helena, Montana over the continental divide 6800ft passes to Anaconda, Montana and an avg of 24mpg. In April I ran from Albuquerque, New Mexico to Las Vegas, Nevada at 70mph and got 24.92mpg .
Adjust the nut behind the wheel and you can squeeze a cupple mor mpg out of it.
Use the Torque App (or similar) and monitor your IAT ( intake air temperature)and block your raidator till you start seeing an increase. Then back off 5%, open the hole 5%larger. The size of the hole will be different for winter and summer, and wether or not you have grades to pull, and loads over 1500lbs.
Based on a long conversation with a Cummins tech. 45-60°f is ideal IAT or as close to ambant if ambant is above 60°f can be 20-50° above ambant. Per Cummins for every 10° above 60° f there is a 1%loss of power. EG a 250hp engine will only produce 240hp and buen 250hp worth of fule. At an IAT of 90°f.

Why not have an electric heater warm the DPF to regenerate?