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Discussion Starter · #1 ·
I have an 06 5.9 ccsb with a 2in lift everything else is bone stock (never tuned, stock transmission, pre def, stock exhaust). I’m only getting around 14mpg highway and 11-13 combined. Is this normal? I thought the 5.9 was supposed to get a lot better mpg. Oil change, fuel filter, air filter not too long ago any help or advice is appreciated thanks in advance!
Automotive parking light Wheel Tire Plant Car
 

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I had a 97 5spd 2500 3.54 and an 03 6 spd 4.10 drw, both rwd, concurrently for 8 months and both got exactly 21.0 commuting to work. Both of them had towing turbos and careful tuning but the mpg didn’t change from any of that. 04.5 was higher power and I think In-cylinder egr and mpg went down but I didn’t think that much.
 

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Discussion Starter · #3 ·
I had a 97 5spd 2500 3.54 and an 03 6 spd 4.10 drw, both rwd, concurrently for 8 months and both got exactly 21.0 commuting to work. Both of them had towing turbos and careful tuning but the mpg didn’t change from any of that. 04.5 was higher power and I think In-cylinder egr and mpg went down but I didn’t think that much.
Do you know what could cause lower mpg? This is my first diesel
 

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1st thing I would check is Brake drag, jack each corner up and spin the wheels to check. What tires are you running and what size? Have you had a front end alignment lately? How is the truck used, how much weight in the bed? All these things can add up to mpg loss.
How many miles on the motor? The injectors could be getting old. Any smoke out of the tail pipe, if so what color? Need more info.
Just an for instance I recently changed buying fuel from Shell to a Speedway closer to my house and lost 1 mpg due to I believe more Bio in the fuel, the point I'm trying to make it there are many variables to mpg.
Larry
 

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Your lift is hurting by approx 1.0 mpg and the numbers you mention seem low for sure. I would start by swapping the map, cam & crank sensors (cummins only on cam & crank) and re-evaluate. If you want cheap mpg bumps then consider a 200* t-stat and the side bed seals from the top of the bed, trimmed down to the body line that goes to the top of the bumper. Your looking at less than $50 for both if you get the seals at a wrecking yard. They come off the 4th gen 1500s.
 

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My dad's 06 QCLB dually gets about the same mileage with stock lift/tires. Injectors have been replaced worm stock injectors with brand new recently and fixed minor injector issues but mileage didn't improve.
 
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Skinny peddle operation can change fuel consumption 30%. Driving style and using CC can make some big swings in MPG. I've been retraining my skinny peddle operation. I was surprised how better economy improved.

At this age, sensors, fuel relief valves, battery cables are all suspect after checking for brake drag. I've replaced sensors and check for brake drag. Also replace all battery cables, add ground cables and such.

I found there is no silver bullet for better fuel economy but many small changes.

Mileage Increased from 18 to 21 After

23 and 25 MPG over 1300 mile Solo Trip
 

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I'm thinking the same about mileage, injectors and if it smokes. My 12 is one of the bad mpg years and I have it tuned so mildly, it won't smoke even if I try. I average 10, nearly always towing 15k and I'm never unloaded long enough to find out what the mpg can get up to.
Check yours for boost leaks... tighten the clamps and check for boot connector holes. A pressure test is the best. I also think yours has a cat in the exhaust. My 97 cat was plugging up already at 19k miles and I punched the core out of it. That restored the power but I don't remember if it affected mpg.
 

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Discussion Starter · #10 ·
1st thing I would check is Brake drag, jack each corner up and spin the wheels to check. What tires are you running and what size? Have you had a front end alignment lately? How is the truck used, how much weight in the bed? All these things can add up to mpg loss.
How many miles on the motor? The injectors could be getting old. Any smoke out of the tail pipe, if so what color? Need more info.
Just an for instance I recently changed buying fuel from Shell to a Speedway closer to my house and lost 1 mpg due to I believe more Bio in the fuel, the point I'm trying to make it there are many variables to mpg.
Larry
Thank you, the tires are 285/75/18, it may need a front end alignment I’ll look into it, I tow for work about half the time and get 11-13mpg including the empty weight on the way back, the rest is city and highway driving and I’m very very light on the peddle (under 2k rpm, usually go 65 on the hwy), 0 weight in the bed, 209k miles on the truck, and it never smokes.
 

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Towing just about ruins any chance of getting good fuel mileage. As to the size of tires and rims they won't help at all with the exception of possibly a slight gain running empty on the highway.
I'll assume you have 3.73 gears, with larger tires especially in town and Towing there is more rolling resistance than a stock size, when cruising down the highway it may help a bit with the larger tires.
As to these trucks getting great mileage, some claim they do real well but I believe that's either folks looking at the lie o meter and not hand calculated mileage.
For instance my 03 with stock tires and rims driving with about 500 pounds in the bed at all times gets 14.6 hand calculated driving in town and some rural driving up to 55 mph. On the highway I have seen 20.8 mpg but I do not drive highway often. I don't tow anymore but I would assume my mileage would be somewhat close to yours. I think if Everyone hand calculated their mileage the numbers truthfully reported would be very interesting to say the least.
Larry
 

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Discussion Starter · #12 ·
Towing just about ruins any chance of getting good fuel mileage. As to the size of tires and rims they won't help at all with the exception of possibly a slight gain running empty on the highway.
I'll assume you have 3.73 gears, with larger tires especially in town and Towing there is more rolling resistance than a stock size, when cruising down the highway it may help a bit with the larger tires.
As to these trucks getting great mileage, some claim they do real well but I believe that's either folks looking at the lie o meter and not hand calculated mileage.
For instance my 03 with stock tires and rims driving with about 500 pounds in the bed at all times gets 14.6 hand calculated driving in town and some rural driving up to 55 mph. On the highway I have seen 20.8 mpg but I do not drive highway often. I don't tow anymore but I would assume my mileage would be somewhat close to yours. I think if Everyone hand calculated their mileage the numbers truthfully reported would be very interesting to say the least.
Larry
Thank you, you have been a big help
 

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If your really motivated and plan on keeping your truck for years, this thread has a lot of what I did to my truck to help me get up there in the mpg numbers...


Followed by


all leveraging lessons learned from...


and summing it up with...



Note that the E-water pump failed at ~14k miles with bearing failure.


If I were starting from scratch, my mpg order would be

1) 200* t-stat with 1/16" bleed hole $20
2) ATS Arcflo intake elbow $320
3) Custom tuning via HPT $400 minimum
4) V3 of the stock air box mod, results from V4 coming so still unknown which is better ~$170
5) AFE Torque Tube $100
6) AFE stainless (or not) exhaust manifold $600 (iirc)
7) 64mm HE351CW turbo ~$1500
8) Stock downpipe with cat $free
9) 30" mangaflow muffler $unknown
10) Would try the Flex-A-Lite fans but divide the shroud between the fans. $unknown


ROI would take a while if done at the same time, mine evolved over the years so it is spread out.
 
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Mileage seems low, my 06 QCLB 6 speed manual got those numbers towing up to about 7000 pounds , stock,

autos seem to do better on mileage

I would suspect front end alignment, injectors, air filter, boost leaks, intercooler, etc
 

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I see you have what looks like a wide traction type tire, they can cost you fuel mileage along with your right foot. My old 06 was 100% stock with factory 265/70/17 Michelin tires, I would average 15-16 town 20+ hwy (summer 1-2 lower city winter), once I put new tires on it I lost 2 mpg hwy 3-4 mpg city, the tires were I put on were Michelin LTX A/T2, I should have waited for the the Michelin M/S2 All Season tires....
 

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I am sure it is about how and where you drive.
 

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My 06 gets 17-18 city (hand calculated) with 285x75 AT tires. I was getting around 15 (hand calculated) on stock tune and increased with the smarty jr.
 
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