100 posts in this topic

Hi, shep67...Yes, our 2005 5.9L HO did deliver the very best mileage closer to 1600 rpm.  Actually, the "window" for maximum efficiency was 1600-1900 rpm, with 1600-1750 working best without a load. 

 

I shifted the entire dynamic with the oversized tires, lift, added weighty accessories and bumping the curb weight to around 8,900 pounds.  Mileage hasn't approached those early levels since, and the axle gearing change to 4.56 from 3.73 was somewhat overkill, a straight adjustment for the new 34.6" tire diameter would have been 4.10.  (With the added weight, 4.30 gears would have been great but were not available when I did the gear swap.)  The added weight makes the truck lean toward the Cummins commercial recommendations, which call for 2,100-2,400 rpm for best efficiency.  I now stay in the 1,980-2,100 rpm range since adding the Hypertech software tune.  I have squeezed some decent mileage in the 1,800-2,100 rpm driving range.

 

If you have the 48RE automatic, a short bed, quad cab and 4x4 system, 3.73 gearing and single rear wheels, stock size tires, no software tuning, light if any accessorizing, few other modifications and no chassis lift, your truck is identical to our 2005 when it was new.  Play with the 1600-1900 rpm range.  You'll be very pleased with the fuel efficiency.  I once reached 25 mpg unloaded and regularly achieved 23-24 mpg.  We pulled a car hauling trailer with our Jeep XJ Cherokee on board (GVW around 5,400 pounds for the trailer and Jeep), and I averaged 17-plus mpg at interstate speeds, including the grades en route to Moab from the Reno Area via I-80, I-15, U.S. 6, I-70 and the road into Moab.  I trailered in the 1600-1900 rpm range wherever possible on that trip.

 

Overall, the faster you spin the ISB Cummins engine, the more fuel it uses, regardless of load...It does deliver best fuel mileage and pulls strongly at 1,600 rpm in stock tune.  As a footnote, I have a friend whose 2004 has a manual transmission, and he upshifts each gear at 2400 rpm.  (For maximum fuel efficiency, I would target a 1400 rpm upshift with an unloaded truck on flat ground and either an automatic or manual transmission.)  His highway cruise speed is faster than mine.  He has never achieved over 18 mpg with his 2500 4x4 long bed.

 

I give Chrysler and Cummins a lot of credit with the 5.9L H.O. Cummins tune.  The engine is strong, and the quick torque rise is very helpful for cruise, fuel efficiency and even towing.  There is also the stamina of the transmission to consider.  The 48RE is okay, not fantastic, the NV5600 about the same despite the ravings about their durability.  Were I to purchase our truck new again, with plans for all of the modifications to date, I would likely have gone with a manual transmission, the G56 six-speed was available.

 

Moses

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Hey Moses, I started reading this thread and think you might be able to help. My major concern isn't fuel mileage (I normally never drive over 65-70mph empty or loaded). I have a 2005 ram 3500 4x4 single rear wheel automatic that I pull our older holiday trailer with. I have 33" tires, aftermarket exhaust, cold air and a bully dog programmer that's set go the "tow" setting. The truck normally gets good mileage but when I'm pulling our trailer (or any trailer for that matter) the truck doesn't seem to have the power it should. I cannot seem to locate where it states the gear ratio but I'm assuming it has the 3.73. Any ideas as to what I can do to increase torque? I've replaced the transmission once before. I replaced it with another 48re (same as factory) and I don't want to do it again. Also, do you have any idea as to the cost of re-gearing the rear end?

Thanks a bunch

Jeff

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Hi, Jeff...These Cummins ISB engines are rpm and load sensitive.  You likely do have 3.73 gears, as the VIN can confirm.  The only other factory gearing with the 48RE in the U.S. would be 4.10.

 

Changing to 34.6" tires (35") with a 4" chassis lift, I thought that my exceptional fuel efficiency would improve slightly from the overdrive effect created.  It did not, and in fact, when pulling a trailer, the efficiency plummeted. 

 

The direct "correction" gearing would have been 4.10, but I opted for 4.56:1, planning for trailer pulling and some load relief on the powertrain.  In particular, my concern was the 48RE.  The truck now has great power and clearly less stress on the transmission; however, my fuel efficiency has stayed poor with both the 34.6" and current 34.5" diameter tires and 4.56:1 gearing.

 

I am faced with two options:  1) install 4.10 gears to "restore" the factory gearing with these 34.5"-34.6" tires (35" inch sizing) or 2) install a solution like the Gear Vendors overdrive with the current gearing (4.56).  I plan to discuss this scenario with Gear Vendors and may take the latter route.  That would double the available gearing (allow split shifting) and also provide a true overdriving effect when running empty.  I will update on which approach makes sense...

 

In your case, the option is 4.10 gears unless you want to do an axle gear swap to 4.30:1 or 4.56:1 and also use an overdrive like the Gear Vendors.  I believe you're right on the cusp with 33" tires and likely could be happy with just the change to 4.10 gears.  This would relieve the load on the 48RE when towing but not send the engine rpm way upward.  If your 33" tires are a good setup and permanent plan, this could work.

 

Cost depends upon gear sourcing.  Mopar, Revolution Gear, Yukon, AAM, Randy's and many other suppliers are in the market.  I would lean toward a supplier that uses genuine AAM gears, especially for 4.30 or 4.56 gears.  For 4.10s, a quality set for your year axles would be okay.  (Mopar would supply AAM in all likelihood.)  You naturally need to replace the 11.5" and 9.25" gear sets.

 

Price depends upon hourly labor quoted and the actual price of the gears and bearing kits.  Others may want to weigh in here, as I do all of my own labor.  Shop around but maintain a quality standard here.  If you need in depth how-to information, my Vimeo On Demand video has helped many installers:  http://www.vimeo.com/ondemand/aamaxlerebuild.

 

Moses

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I was kind of thinking that the 4.10 would be the way to go. I was also told by someone that changing the torque converter would also take some stress off the transmission. Thoughts? Worth the money?

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Jeffb6403...4.10 gears do make sense in my view.  For power gains and even fuel efficiency, the 4.10 gears would get the engine into the correct rpm range while towing. 

 

The converter is a known weak spot in the 48RE.  My truck has not been subject to excessive towing chores, and as a result, I've had no trouble with the converter at nearly 140K miles.  Megatron replaced his 48RE with a bulletproof unit and converter.  Others do build these units up, and if I rebuild my 48RE myself, there are specific upgrades planned.

 

With the right gearing and sensible driving practices, I believe you could stretch out the lifespan of your 48RE...We can discuss driving techniques that take a load off the transmission.  We'll open a new topic for that exchange...

 

Moses

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I have a 2005 Dodge Ram Crew Cab with 3.73 gears, 285-70-17 tires, no big bumpers, swb, level kit.  Empty best mileage 15.5 with smarty jr.  Bought the truck with Edge.  Any setting only 14.5 mpg.  4" mbrp exhaust with muffler.  AFE cold air with original injectors at 118000 miles, changed injectors(stock at 120000) no help, same mileage.

 

Turbo looks good intake and exhaust no play.  Pulled injectors sent back for check, pulled compression check at all cylinders in the 470 psi range.  Notice intake was wet with fuel when pulled new injectors wasn't that way when pulled originals.

 

On interstate at 1950 rpm 70 mph or a mixture of 2 lane at 55-60 doesn't seem to make and difference.  With a 7x14 v nosed enclosed tandem axle trailer with 2 harleys approx 1450 lbs trailer weighs 2150 lbs mileage is 9.2 to 9.4 whether interstate or some 2 lane at no more than 1950 rpm.

 

2 questions:  Why is the intake wet with fuel (never have seen a cummins wet, powerstroke yes), and why is the mileage so bad?

 

Should have kept the old 93 Cummins!

 

Thanks,

 

Monty

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Monty, I like your setup, it's nearly what my truck had new, the tires are slightly larger diameter, which does create slight overdrive effect and speedometer error.  Is your speedo corrected for the 285 tires?  OE was 265.

 

Regardless, this error is not enough to account for the very low 9.2 to 9.4 mpg when towing.  You are aware of RPM factor and seem to account for that in your driving.  You might play with an 1800 RPM ceiling and see if that helps.

 

Does your software programming allow for restoration to "stock" setting?  If so, try that just to get a baseline and rule out tuning as the source for low mileage.  You can restore the performance settings if that has little effect.

 

Agreed, your mileage is way off here.  After verifying speedometer, also try testing mileage with actual fuel burned, not just the factory mileage monitor if you're using it now.  I find the factory readouts very misleading.  The only accurate test of mileage is the old fashioned "how many miles, how many gallons" formula.

 

Would like to see this through to an improvement in fuel efficiency...Others should also jump into this discussion.

 

Moses 

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Yes my speedometer is corrected with a smarty for the size tires and I am Hand calculating that all the mileage when I've done it and I have put it back to stock it changes virtually none what about the fuel in the intake I can't find anybody to address that problem thanks Monty

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Monty, I'll encourage Megatron to comment on the fuel pooling in the intake.  He has done a variety of tune measures, turbo mods, exhaust work and a Hamilton camshaft on his 5.9L Cummins.   

 

Have you checked fuel rail pressure?  This is an electronic common rail diesel (CRD) injection system that requires regulated fuel pressure at the rail...Over-pressurizing will create too much fuel flow. 

 

Moses

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Hey Monty,

 

  So you have a wet intake and you are certain it is fuel? I am perplexed as well. The only thing that fuel and the intake have in common is the fact the fuel rail sits on the intake plate. Other than that they are separated by steel or aluminum.

 

  So my question is, if you were only pulling injectors how did you see in the intake? Were you just looking through the grid heater/intake horn inlet or did you pull the intake plate and rail off? Also, was the intake elbow itself coated with this liquid or just the valley of the intake itself? I know with bad turbo seals you can get oil that far into the system, but it should look like oil not diesel. Did you do anything else during the injector swap?

 

  I mean without a cracked head nothing really shares the passages. If it was a cracked connector tube passage it should leak into a water jacket before it made it onto the intake area. If it was a bad sealed connector tube it wouldn't leak into the intake, it would leak out or you would get a lot of fuel bypassing the injector and going out the return. If any of the fuel lines were cracked or leaking it would be on the intake not in it. If the rail or returns leaked it would be on the intake not in it. Fuel filter bowl is below the intake on the block so that's out, plus it would leak onto the ground. There is the fuel return from the back of the head but its passages don't cross with the intake. Generally when that one leaks you see it dripping from the bell housing.

 

   Do you have any fuel pressure gauges or a way of checking rail pressure with your choice of tuner boxes? With good compression, good rail pressure and new injectors you should be golden. If your turbo is sealed up good and no boost leaks in the system, you should be running like a champ.

 

 Now, your cam does have EGR properties built into the profile of the grind, I believe that started in 04.5. What this does is overlap the intake valve opening with the exhaust valve closing at the end of an exhaust stroke. It pushes a bit of exhaust back into your intake to be re-burned on the next intake and compression stroke thus making you EGR compliant.  Sooo, on the most complex explanation I can think of, not including solar winds, is that one of your first rebuilt injectors (if not all of them) were leaking off into the cylinder when you turn it off and then when you first start it up it pushes some raw fuel back into the intake. However, this would make for some bad startup smoke and you would probably find fuel in the oil as well. Plus I would have to assume the engine would reclaim this fuel and it wouldn't be sitting in the intake for a later discovery, unless it was a lot.. To me that's crazy and I would almost rule it out, but its the only path for fuel to even come near an intake runner leading back to the intake. I mean any other explanation would include some bad running habits if it ran at all. So the simplest explanation is that during the second removal you let some fuel get into the intake without you noticing it during disassembly and then discovered it. But if you only pulled the grid heater, then this would be hard to do.

 

 You didn't over tighten or use the wrong bolts putting the injectors back in and crack your head did you? I don't think this could lead to an intake runner but I don't have a good cutaway to confirm what touches what in the head.

 

  To be honest I'm at a loss. I have never heard nor could I find anyone with this issue. Do you have any other symptoms other than not so great fuel mileage? Also why the original injector change to begin with? Did you have any signs of bad injectors like hazing or no power? Who did the injector work and did you get the results from testing back with them? I had the same set rebuilt twice because they failed testing the first time, so it happens.

 

 As for MPG's, yours isn't the worst I have seen. Idling for warm-ups or trips into the truck stop for snacks really cuts down on any gains. I did a lock out conversion on my truck for some small gains as well, but that's not a cheap gain but it will pay off over time. For towing you should check into a water meth injection system like the ones from Snow Performance. It helps keep the EGT's low and will help with the MPG's as well. Although it is a power adder that requires refills, it may help offset the big loss you see with towing. That should help payback the investment for the system.

 

 Let me know on the couple of questions I had and I will see what else I can help with.

 

Dustin

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Monty, the engine's fuel pressure and injector systems have a number of prospects for excessive fuel delivery.  Here are details on both fuel delivery and the injector system for the 2005 Dodge Ram Cummins 5.9L with "late style" injection:

 

2005 Dodge Ram 5.9L Cummins Fuel Delivery at the Engine.pdf

 

2005 Dodge Ram 5.9L Cummins Fuel Injection.pdf

 

There should be a number of clues here.  This and Megatron's comments will be useful to diagnosing and pinpointing your fuel consumption issue. 

 

Let us know what you turn up...

 

Moses

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Wow I must say that whole thing was quite the read, I think it may have answered my questions I've been having for a while now and if I understood everything correctly I've been going about better MPGs the wrong way however I am achieving one of my goals keeping it cool (temp wise)

 

To start I have an 05 Ram Quad Cab with the following:

G56 Transmission

3.73 rear axle

4" exhaust no cat just a Donaldson muffler

ATS manifold, k&n tube with AFE 7 layer filter

S&B intake elbow

EDGE juice with attitude 

Cari lift (3" in front, and add a leaf in back) 

35" toyo M/t's

 

My goal with this truck is to have something that is pretty to look at and get great(18+) gas mileage. So far its just easy on my eyes and not on the wallet. It would appear that my first mistake was putting the 35 M/T's, I knew the M/T's would hurt my MPG but going from my 305/55/20 (33.23) A/T tire to my 285/75/18 (35"x11.25) crushed my mpg's by about 5mpg. At first I thought it was due to the M/T tread but now it looks like it was me going to a 35" with my gearing ratio. Recently I was pulling a 26' horse trailer and my mpg was beyond horrible, under 12mpg. It was at this point I figured I needed to figure something out, my first thought was with a 34" highway tire now it looks like I might need to go smaller.So with the G56 and the 3.73 rear I should be looking more towards a 32"and under tire or because I have a G56 can I get away with a 34" highway tire and still get decent gas mileage. I know my mods to my truck may not let me get the 20+ mpg's but I would love to get as close to it as I can as I got 4 1600 mile trips in the next month 3 of which pulling a trailers. 

 

Any advice you can give would be so greatly appreciated, and thanks for all the interesting posts from above.

 

ADDED: If I were to keep putting on 34/35" A/T and H/T tires what would be an optimal/cost efficient rear end a 4:10's?

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blacklamb...We're in nearly the same predicament.  Your G56 versus my 48RE is the most significant difference.  I had exactly the same experience going to 34.6" tires with the OEM 3.73 gears.  Your direct match for the 3.73 at the current tire size is 4.10 gears.  My options are either 4.10 gears or keeping the 4.56 gears I installed and adding a Gear Vendors overdrive.

 

Will keep you posted on my choice(s) here.  3.73s and 34"-35" tires wrecked the fuel efficiency.  4.56s give the truck enormous power but poor mileage due to too much rpm at cruise speeds when unloaded.  4.10s were the direct replacement, though I'm carrying over 1000 pounds of accessories and add-ons, and the truck would be slightly underpowered with 4.10s and 34.5"/34.6" tires.  4.30s might be a compromise.  This ratio was not available when I installed 4.56 gears.  With 4.30s, I would not expect the same mileage as stock with 3.73s and 265 tires, though the added accessories would be covered in performance terms.  Additional weight drops mileage in any case.

 

I'm targeting 22 mpg unloaded for a currently estimated (not proven, need to run over scales) curb weight around 8900 pounds with both tanks of fuel full.  Towing a 7,000# travel trailer, I would like to see 16-17 mpg.  Target engine speed at interstate mph will be 1700-1800 rpm +/- 100 rpm.

 

Moses

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Hmm I wonder if I can pick up a set of 4.10 gears relatively cheap and call it a day, something tell's me I could. 

 

The exact tire I'm looking at getting is the Nitto Terra Grappler 285/75/17 (33.86) which is basically a 34, however they are weigh almost 20 lbs less per tire than my Toyo M/T's so I bet I would see a decent change. 

 

They sure made this truck capable of some awesome MPG's but if you want a good looking truck you better have a deep wallet...

 

I was making an effort today changing my driving habits based on what I've read above but that went out the window when the fire pager went off, but it was a great fire!

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blacklamb...The 4.10s are the easiest (relatively!) solution and should work very well with 34"-35" tires.  Let us know how this works out.  The 4.10 ratio is actually a stock option for the Ram 2500/3500, you have many gear suppliers from which to pick.  

 

AAM claims they make the best, easiest to set up gears if you're doing the work yourself.  They claim their tolerances are so close that there's no need to change pinion shim stack thickness when replacing a set of OEM gears as in your case.  Not having to trial fit the pinion depth saves considerable time. 

 

If you're doing the work yourself, my 11.5"/9.25" AAM axle rebuild how-to is a popular streaming rental how-to at Vimeo-On-Demand.  I'm very pleased with the positive feedback on this 66-minute step-by-step.  See the trailer at:  http://www.vimeo.com/ondemand/aamaxlerebuild

 

I'm looking forward to your feedback on the 4.10 gear change and tire diameter choice.  Let's get that fuel mileage back! 

 

Moses

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Well as in a pinch and time is not on my side I'm getting some decent used Toyo AT2 tires 32.8" quick and easy as I have the extra set of wheels laying around.

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blacklamb...Worth trying the smaller diameter tires before changing gear sets.  This is closer to stock and will clarify whether gearing or tires can make a difference.  4.10s with these tires would also work.  Let's see what the tires alone will do...

 

Moses

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I'll keep track of my mpg on my first of three 1600 mile trips if not all to see what the toyo at's with 3.73's and I'll keep the RPM's between 1600-1900  in attempt to keep the test consistent. After my move I'll save some cash and swap the diff's over 4,10's and track the mpgs after that and see what the difference is. I'll be doing the trip twice loaded and one empty so it should be a decent test.

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Looking forward to the results, blacklamb...Keep us posted! 

 

The 3.73s with 32.8" tires make a good experiment.  This is not as radical as 34"-35".  Stock was 31.9".  Do you have any idea what your gross vehicle/combination weight for these trips will be?

 

Moses

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Sorry took so long to get back to you moving is less then fun.

 

The other day we got the trailer weighed empty with a total of 17k (both truck and trailer) I'm sure one the horses, water feed and what not we will be over 20K but that trip isn't until Sept.

 

The other pull with be a Uhaul car transport with car and crap to get my life started again so should be around 12-14k total weight. 

 

I picked my truck up from getting the manifold put on and and some other maintenance done. I had my new tires for the trip and set my cruise at 60 mph (1856RPM's) and the lie "o" meter said I was getting 26.8 averaged over the 100 mile trip (didnt hand calc it yet). This was a improvement ready from the 19-20 mpg read I would get with the lie "o" meter (hand cal at 15-18 depending on time of year and driving highway or not) with my 35's. 

 

I'll be interested to see what doing it by hand will net me. 

 

Well back to getting house crap done :/

 

EDIT: My Mods to my engine are now:

 

K&N intake tube with AFE Filter: http://afepower.com/technology_detail.php?tech_id=6

S&B intake Elbow (its impressive how much the stock came to a pinch point) http://www.sbfilters.com/index.php/intake-elbow-76-1004.html

ATS Ehaust Manifold http://www.atsdiesel.com/ats2/productdetail.asp?p=2049202272

4" Exhaust, no cat and Donaldson straight muffler) http://www.ryderfleetproducts.com/donaldson-m085171/muffler-4"-in-4"-out-p-w26-m085171

Edge Juice with Attitude 

 

I don't plan on doing anything else engine wise to my truck as I feel I got all the choke points out and now she can breath easy and run cooler, ok thats a lie, I'm debating replacing my edge with a smarty (http://smartyprogrammer.com/products/smarty-touch)

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Appreciate your taking time out of the move to share info.  Enjoyed your reference to "lie-O-meter", if we depended on the factory meter, we'd all be stuck alongside the road with a fuel can fill or our thumb out.

 

Pleased that you're noticing a "relative" improvement in fuel efficiency prior to hand calc.  The load is significant, I'd think something in the neighborhood of 12-15 mpg would be very respectable for 17K GVCW.  The rpm is the catalyst for fuel efficiency with these engines.

 

Looking forward to your updates...Trust the weather will cool down before the horse haul...Stop at shade trees and lots of un-chilled water!

 

Moses 

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I have a 2004.5 3500 st regular cab dually, with the 5.9L HO. I believe I'm the 4th owner.

Had this truck a few weeks so still trying to get to know it.

As a long haul driver I started applying the progressive shifting method for the 6 speed and jumped from 17mpg to 19mpg, calculated by hand.

This truck has had many different drivers with the last owner and they drove the piss out of it for the sake of hearing the turbo kick in.

My results are from progressive shifting around the 900-1100rpm range for the first 4 gears, then 1300 in fifth and keeping it around 1600rpm in sixth, with no load. You have to bring up the revs when loaded by about 200rpm all the way through. I have yet to stop a Dodge dealer to get a printout of how the truck had been spec'd originally. What i have observed is much what has been in discussion here, as every once and awhile you have to open it up to clear it out, then it seems to run smoother with more power. I do not believe anythings been modified, running stock.

Today I bought used cruise control switches, and will be interested to see the diffence it will make in economy. The companies I've driven for ask that you use cruise whenever possible.

Tomorrow is a long trip from Montreal to London On. to pick up an Ultralight. I'll be pulling a 24ft tilt deck trailer. I'm trying to record all the changes that are happening to the truck as I go along. Light Duty or Heavy Duty trucks, the procedures seem to be the same.

I'm enjoying what I've read so far, I'll keep reading and learning.

The transport truck I was last driving went into the dealer for Dyno Tuning and we got an extra MPG out of it. I'm wondering if I could get the same results with the Dodge?

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Hi, Stormin!  This engine rates its torque peak at 1,600 rpm.  Your driving style and findings are right in step with the torque rise and my experience with fuel efficiency.  Your 6-speed provides more control than the 48RE four-speed automatic in my '05 HO model, but the results seem the same.  I basically use the same upshift points under light throttle, a similar approach!

 

"Tuning" in the case of our CRD engines is really electronic or ECU software programming.  In my findings, the Chrysler OE tune is mild and focused on emissions, fuel efficiency and a very quick torque rise to accommodate taller axle gearing.  I got my best all-time fuel run (25 mpg over 500 miles, varied terrain and running empty) with 3.73 gears and stock tires (265R70x17), no accessories or added weight, just a stone stock truck.  I ran rigidly between 1600-1900 rpm at cruise with the kind of upshift rpm points we describe when rolling from a stop. 

 

In this forum topic, I've characterized the modifications and changes to the truck since that point, the added weight, the Max Energy (Hypertech) tune package, which raised torque peak to 2100 rpm, the retrofit gearing to handle trailer pulling with 34.5" to 34.6" diameter tires, and so forth.  4.10 axle gears would have been the direct change to compensate for the increased tire diameter.  I installed 4.56 gears after considering a change to 4.10s, the added 1,100 pounds of accessories and auxiliary fuel, loss of aerodynamics and the expectation of pulling a 7500-plus pound travel trailer on a regular basis.  I'm sticking with the 4.56 gears and plan to back out of the throttle (cruise speed decrease) to get the rpm closer to 2,000, at least when trailer towing. 

 

As for fuel efficiency, these engines are hypersensitive to rpm.  The sweet spot is the only spot for fuel efficiency, and as you know from over the road commercial diesels, driving faster or pulling heavier loads simply means more boost and fuel flow.  I like the Hypertech Max Energy performance and would likely not attempt to "de-tune" the engine to reclaim lost fuel efficiency.  Hypertech actually expected my mileage to improve with the tune, and maybe it did, but the modifications to the rest of the truck took place at the same time.  The resulting fuel mileage reflects those changes. 

 

We can't add weight, decrease aerodynamics and gear lower (numerically higher) without expecting a ding in fuel efficiency.  I'm getting consistent 21-22 mpg if I hold to 1980 rpm or less at cruise on the flat.  When I exceed this rpm, like trying to maintain 70-75 mph posted speeds on Nevada interstates, the mileage drops proportionate to vehicle and engine speed.  69 mph is my maximum road speed for squeezing 21 mpg these days.  65 mph is better.  55 mph (California trailer pulling limit) is even better.  All mileage gains are engine rpm related...The truck works very well as a "hauler" at trailering speeds between 55-65 mph.  With current gearing and tire diameter, plus the added curb weight of the truck, I got 14 mpg when pulling an 8500-pound travel trailer last year.  My current target is to squeeze 14-16 mpg with a 7500-pound travel trailer in tow...In stock form, the truck could achieve 17 mpg with a car hauling trailer and XJ Cherokee Jeep on board.

 

Moses

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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. 

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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

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