2001-early 2004 LB7 Duramax Fuel Economy Poll

[schaack2]

Just checked my 2003 crew/short box today and I got 17.3 - only current mod. is 4" exhaust. This tank I just check I had been pretty heavy on the throttle with a lot of town driving. Previously checked tanks were high 18 / low 19 (all calculated manually).

After reading through all the differences in fuel economy, I'm curious which variables make the biggest difference in fuel economy. I've got a laundry list of upgrades to make, regardless of economy, I want to make larger burn-outs!!

How much affect do you guys feel a bed cover or topper makes on fuel economy? I've never had one on a truck but it has to significantly reduce drag (at least one would think). After reading all posts, two of the guys with the best economy had either a topper or a bed cover. What are the thoughts of everyone else on this matter?


Schaack2

[SDakDmax]

19 to 20 going 55 - 60 no problem, if I get my foot into it and go 75, it will drop to 16.. I think this is good.. the best part is the power when you get your foot into it, and towing..

[diesel dissapointed]

I hope this post saves some poor guy from thinking he can get the mileage #'s some of you guys are posting.I am on my second duramax after lemon lawing my first one.Total mileage over 100k and neither truck ever saw over 17mpg,that includes empty, downhill,tailwind,drafting,etc.This is a reg. cab 4wd 9,200 gvw truck that usually runs 65-75 with cruise control @ sea level.P.s.I've been a professional mechanic over 30 years and this truck has been on the dyno and had parameters checked with a tech 2 @.worst mileage was 9mpg towing 10K lb boat

[DRINKDIESEL]

Getting an easy 20mpg highway. Up to 23 on longer trips with '04 EC LB 4x4 SRW and the Juice with A2 set on milage(#1). Also installed a K&N air filter and modified the stock air box which helped a bit. I'll keep working on it.

[DmaxMaverick]

Getting an easy 20mpg highway. Up to 23 on longer trips with '04 EC LB 4x4 SRW and the Juice with A2 set on milage(#1). Also installed a K&N air filter and modified the stock air box which helped a bit. I'll keep working on it.

Just curious.
Is that mileage from the DIC, or are you calculating manually?

[DRINKDIESEL]

From the DIC. I was getting ~17 before the mods on the DIC.
I'll calculate it out on the next fill up.

[DmaxMaverick]

The reason I asked, is when using a power adder, the DIC tends to become quite optimistic. Usually, a very disapointing reality is discovered once the mileage is calculated manually. This inaccuracy is normal and consistent with the operation of the module/programmer. Problem is, the manufacturers don't disclose this in their literature. Most folks just go on thinking the mod has given them great mileage.

Please get back to us with your results. Some folks reported the DIC mileage was still accurate with a module installed. If one can do it, they all can. There's no reason to not have the DIC calibrated, if it's possible. In either case, we should either have a calibrated DIC, or a formula to determine actual mileage from the DIC info.

[DRINKDIESEL]

The reason I asked, is when using a power adder, the DIC tends to become quite optimistic. Usually, a very disapointing reality is discovered once the mileage is calculated manually. This inaccuracy is normal and consistent with the operation of the module/programmer. Problem is, the manufacturers don't disclose this in their literature. Most folks just go on thinking the mod has given them great mileage.

Please get back to us with your results. Some folks reported the DIC mileage was still accurate with a module installed. If one can do it, they all can. There's no reason to not have the DIC calibrated, if it's possible. In either case, we should either have a calibrated DIC, or a formula to determine actual mileage from the DIC info.

Gimme a couple of weeks. I'll reset the DIC at the next fill up and compare.
You've got me worried now.
K

[DRINKDIESEL]

The reason I asked, is when using a power adder, the DIC tends to become quite optimistic. Usually, a very disapointing reality is discovered once the mileage is calculated manually. This inaccuracy is normal and consistent with the operation of the module/programmer. Problem is, the manufacturers don't disclose this in their literature. Most folks just go on thinking the mod has given them great mileage.

Please get back to us with your results. Some folks reported the DIC mileage was still accurate with a module installed. If one can do it, they all can. There's no reason to not have the DIC calibrated, if it's possible. In either case, we should either have a calibrated DIC, or a formula to determine actual mileage from the DIC info.

Sorry it took so long to get back to you. Things are hoppin' at the shop here.
Here's the results of the DIC to actual.
513.8 miles-crappy single lane small town type
102.0 litres which equals 27.01 US gallons
19.02 MPG Calculated
19.4 MPG on DIC
A slight difference between DIC and actual, but not much.
I ran on level 1 (mileage) most of the time with the A2. I'll see what the DIC says when I pull my 27' 5th wheel with 5 guys and all their gear to the IHRA Canadian Nationals this weekend.
K

[DmaxMaverick]

Thanks for the comeback.

I don't consider less than 1/2 MPG outside of the normal variation, with or without mod's. If you are in fact getting accurate mileage displayed by your DIC, we need to find out why. Like I said, if it can be had by one, it can be had by all. It is interesting that some folks with the same truck and mod, get different results, in regards to the DIC.

What other upgrades do you have on your truck? Tire size, etc.

[JohnC]

Like I said, if it can be had by one, it can be had by all. It is interesting that some folks with the same truck and mod, get different results, in regards to the DIC.

I'd expect it has to do with how far from optimal the injector flow rates are. The PCM only knows how much it is commanding, not how much is actually delivered.

My DIC mileage is always within 1 or 2 tenths of calculated mileage. Same for fuel used.

[DmaxMaverick]

I agree. However....

Under the same circumstances, some are off by several MPG, and others, like yours, only tenths. I'd like to ID where they depart from common. All things being essentially equal, the results should be equal. But, they're not.

[DRINKDIESEL]

Maverick
The truck is pretty much stock other than the A2 and K&N stock type air filter. I did modify the stock airbox by hole sawing a 2" hole in the lower front part of my airbox. All this seemed to do was make the turbo more audible, which is kind of cool.
The trip to the IHRA drags with about 11,000 lbs in tow and 5 guys in the cab netted 13.4 mpg on the DIC average, round trip. It was 15.1 mpg for the trip down with my trucker buddy being very gentle on the go pedal. This was with the A2 on level 2.

[martanius]

I got 19mpg on my 1st tank of fuel. It was almost entirely highway because we loaded up and went on a trip. Since then I have never hit 400 miles on a tank again. My dad did one time when we were headed to elpaso he managed to get 471 miles on a tank. We pulled a 29'boat all the way back from El Paso to MI and averaged 12mpg at speeds of about 79mph. When I hear people saying they get almost 20 I always assume they are not very good with thier math. I have never even tried to run a tank of fuel at 60mph... that's just nuts.

[DarylB]

As of 85k miles the best mileage to date is
22mpg @ 55mph for nearly a whole tank on the freeway. For every 5mph I lose about 1mpg. I've had the warn winch & guard since it was new so this rig is pretty exceptional. 16-18.5 is the norm without babying it.

[imsweetdaddy]

2002 GMC 3500 C/C Dually I AM GETTING 12-13MPG at 70mph on the HIGHWAY and 10mpg in town. My father has a 2001 Chevy I dentical truck and gets 15-16mpg on highway. What the heck is wrong with my truck??? I have not seen anyone anwhere get suck poor milage as me! ! ! Truck is hard to start 8-10 second range, but if I put a new filter on it it cranks just fine. But after one tank of fuel run through it, it's back to the same hard to start. SOMEONE PLEASE HELP WITH SUGGESTIONS!!! ImSweetDaddy@aol.com I need some help because the 3 dealers around here say it's the injectors, already replaced 2 times. 140k and at 190k. I have 232k now, and that's only 40k on the injectors. This surely can't be the problem. I am diesel illiterate, but I am learning fast. Could my lift pump be weak, but if it is then why is it using more fuel, if it's starving? Truck has no smoke out off tail pipe, ever! Very clean burn, no blow by, uses about 1/2 a quart of oil over about 6500 miles. PLEASE REPLY AND GIVE ME SOME SUGGESTIONS>>> I NEED THE HELP>>> WALLET IS GETTING LIGHT FROM SPENDING IT ON DIESEL! ! ! !

[muncieman]

I have a 2003 Chevy 2500HD crew cab with the allison and my truck has gotten 19.9 as an average for 65,000 miles. It has on several trips been in the 24 mpg rage. It is a 2 wheel drive version and bone stock.

Now if we could just get the lousy fuel companies to charge a decent price for the fuel

[BozDMAX]

I first noticed the difference between the DIC and my actual mileage in March '05 and have been tracking the difference since then. After throwing out some obvious outliers I ended up with 106 data points and using a least-squares/best fit methodology can pretty much estimate my actual mileage by the following formula:

Actual MPG = .86*DIC MPG + .74
R-squared (if you remember your statistics course) is .86 - not terrible given the wide range of conditions (towing vs. non-towing, hills vs. flats, changing altitudes, etc).

so, 20 MPG on the DIC would work out to about 17.9 on my slide rule (anyone else remember those?) with the actual data.

All the data is after the Banks system. No idea if the early data for the first year before the Banks was more reliable or not.

You can take the retiree away from cost analysis, but you can't take the cost analyst out of the retiree...:-)

[More Power]

2001 GMC 2500HD Crew cab shortbox 4x4 LB7:

1820 miles - round trip from western Montana - Las Vegas SEMA show. Each 910 mile leg took 13 hours and 20 minutes, for a 68+ mph average speed (which included fuel & convenience stops). Where possible, the truck's speedo hovered around 85 (65 through Salt Lake and in the mountains north of Salmon, ID on US-93). Calculated fuel economy for each tank ranged from 18.5-mpg to 20.2-mpg. Best tank was the last leg from Idaho Falls, ID to Missoula, MT. Just me and about 100-lbs of gear in the truck. The 265 Michelins were aired to 70-psi front and 60-psi rear. Mobil Delvac 1 synthetic in the engine. Power Service fuel treatment used at the recommended mix ratio. One tank was B5 (Sinclair station in LV). Otherwise, all tanks but one were ULSD. And.... the VanAaken module was turned off for the entire trip.

Jim

[SoTxPollock]

Pretty impressive running 85 averaging 68+ and 18.5 to 20+ mpg. Your truck is right in every way. I may be able to come close to that. I've made 17.2 at 92 and 22+ at 63. I could never drive 55 for a whole tank full, would probably fall asleep. I'm suprised to find out it hasn't dropped below 17.3 with juice on level 4 for a month now. I think my truck thinks its a corvette the way the engine responds, but amazing that the mileage isn't hurt much. My lifetime average for 90,000 miles is still in the high 18's. Great Truck. I've been running the exact same air pressures you have too. However I'm having to back that down now, they're showing wear on the center more than on the sides. Noticed it more on the rears, but I know why.