Maximizing LLY fuel mileage

[Stlheadake]

By all means, hand calculate the mileage. Try to use the same pump, and use the pump the same way each fillup. I normally just set the pump on the middle speed setting, and remove the nozzle once it kicks off.

A larger exhaust system and free-flowing muffler can have a small effect on fuel economy - but not the 3-4 mpg you're looking for. I'd get gauges first....

Jim

Thanks Jim, you and everyone else on this page are a true asset. I am going to order the guage kit from Kennedy first I guess. Othere than the pyrometer and boost, is there something IN a gauge that I should be looking for?

[More Power]

Gauge brand, model and mounting location are largely personal choices.

Have a look at the 2005 Gauge Update to get an overview of what's available for conventional gauges and what sort of mounting appeals to you.

Personally, I like the dual gauge pillar pod for boost/EGT, mainly for visibility - and they look cool there. The Edge Attitude comes in a close second, though I don't know about 2006 model year requirements. The vendors will know....

Jim

[David Proske]

My 2003 and now my 2006 seem to be pretty close in terms of mpg. From what i've seen driving diesels for a number of years.... anyone claiming 20's at 70-75 is flat out fibbing. Or they are going downhill with a tailwind.

[beeler]

I have to agree with David. The only way I could get 20 mpg out of my '02 is if I drive like I'm following old folks to church. On long trips on flat ground with no wind and cruise on 75 I get about 19. Most of the time 17-18. Less in the wind or if I'm in a hurry.

I have the Edge box and a 4" exhaust. I can't say that they really made much difference in economy. Maybe a little. Towing milage is better than stock if you pull the hills at the speed you would have stock.

[Gizmo]

The cost of fuel has modified my driving a bit. Last weekend a 700 mile trip was done mostly with cruise control and 65 mph (slower than I usually drive). The tonneau cover was in place as a couple of threads suggest this does better than my tailgate down theory. A calculated 21 mpg was about 3 mpg better than my normal (lightly loaded (weight) and standard drag profile) . Lower speed and tonneau did make a difference.

Gizmo
2002, 2500HD, 4wd, extended
Stock Duramax/5 speed Allison

[Mark Rinker]

Also, I would hand calculate your fuel mileage as a longterm average over weeks and months, not single tankfuls. A spreadsheet is a great way to do this. Just a moments worth of data entry, or enter the information off your fuel card statement each month. My Holiday and Shell cards record mileage at the pump at the fillup, so its really easy to do by the month. I know when a particular trucks performance has changed, usually a dirty air filter is to blame.

You'll soon settle into a number that will be noticable when you change something like intake/exhaust, etc. When you complete the mod, start another longterm average over a number of weeks and tankfuls. Then and only then will you know if you have truly picked up a solid increase in MPG.

[ToddMeister]

This past winter I made some trips to snowmobile and got 20mpg at 70 mph hand calculated (on winterized fuel, too). I filled up the truck, hit the expressway, drove a couple hundred miles to our destination, and filled truck up. I did this 3 or 4 times. No fibbing here...

My 2003 and now my 2006 seem to be pretty close in terms of mpg. From what i've seen driving diesels for a number of years.... anyone claiming 20's at 70-75 is flat out fibbing. Or they are going downhill with a tailwind.

[Kennedy]

I can't get 20's at 70 mph, but at 60-ish mph I can run solidly into the 20's. It will be interesting to see what Uncle Wally reports as I just sent him a tune for his dually. The DIC shows encouraging results so far, just need to hand check to verify...

[Uncle Wally]

Just to give a comparison as to what my fuel mileage was before John's tune.

05 LLY Crew Cab Dually - stock tires.

Loaded - light to moderate

Modifications at the time were John's 4" exhaust, Uni Air Filter, Mega Filter and Lift Pump/Fuel Pump Pickup mods. I had EFI Live at the time, but chose to leave the stock tune in it for a while.

I was pulling a two place snowmobile trailer with two snowmobiles on it and I had one snowmobile in the bed. There were three of us and our gear in the truck. We added two honda three wheelers to the trailer on the way back.

I drove from Minneapolis to Island Park Idaho in March this year. Temperatures were in the mid 40's for most of the trip out and in the low 60's for most of the trip back.

My best fuel mileage per tank - hand calculated - was 12.5. That was treating the throttle like an egg, using cruise at 60 and never letting the tack go over 2000 rpm.

My worst fuel mileage per tank - hand calculated - was 10. My personal belief is that I got a batch of marginal fuel. I didn't change my driving style much, so I don't know of any other explanation.

Unloaded - with tonneau cover - EFI Live now installed - only changes to the tune were to EGR controls. No added fuel, no altered timing.

I get my best mileage at 50-52 mph. Treating the throttle like an egg, never letting the tack over 2000 rpm even on acceleration. I can get between 16 and 18 mpg. I drove this entire tank of fuel - no wife variables on this one.

I usually don't drive that way day to day, nor does my wife. Normal driving yields a pretty consistant 14-15 mpg.

The only issue is that I spoiled my wife with the new truck, and she won't drive our gas miser car anymore. My wife drives totally different than I do even with me giving her constant grief. Her fuel miser skills have gotten better, but are still not at my level. She only understands two pedal postions: foot completely off the pedal, and the pedal all the way to floor (for both foot feed and brake pedals). With that said, it's hard to get a good fuel economy run when my wife drives. I will work on that when we head to Pittsburgh in July. That way I can actually show her what I am talking about.

Sorry for the long post, but I thought it would be good for a comparison. I installed John's tune yesterday and drove about 45 miles on it. Fuel mileage on the DIC was astonishing. I won't give numbers at this point as I need to hand calc it. You'll here from me after a couple tanks of fuel.

Waldo

[Kennedy]

Just FYI, the changes made should not have had a big impact on DIC readings, in fact, should be none at all...

[REDTRUCK05]

Are you happy getting 14-15 under normal driving conditions? U say your best milage is at 50-60 mph? That makes sense, its logic. People just dont drive that slow on the interstate in Mpls. I like to drive the speed limit 70 mph. If I do this I get between 9 and 11 mpg, pulling 5600 lbs. If I treat the pedal " like an egg shell" unloaded I can get 14 - 15 at 70 mph. If i slow it down to 60 mph ( only when I have to ) I can get 16 - 17 mpg. Do you guys really think these numbers are ok? I think not...

[REDTRUCK05]

I can't get 20's at 70 mph, but at 60-ish mph I can run solidly into the 20's. It will be interesting to see what Uncle Wally reports as I just sent him a tune for his dually. The DIC shows encouraging results so far, just need to hand check to verify...

Let us all know how ur new tunes do. Why is your 05 for sale?

[Kennedy]

Let us all know how ur new tunes do. Why is your 05 for sale?

I'm waiting for more feedback from my testers. I started another tester at the Rendezvous.

I'm not really pressing to sell my 2005, but I put it up in anticipation of acquiring a 2006 LBZ.

I expect 19-20+ mpg from a single rear wheel truck driven at approx 60mph. My MPG drops at 70, but seems to drop less with tuning.

[JoeyD]

Easy driving is key to higher milage. I have not done any highway only trips in my Express but I average 17.5 all the time. I keep speed under 70 on the highway and take off easy in town.
I would think 20 is possible on the highway is you keep it under 70. With the 6spd ally you guys in the 06's run maybe better

[sb359]

best i've done is 20.1 mpg empty and 15 mpg pulling a 6800lb travel trailer

[ToddMeister]

Recently took a long trip to the East Coast over Labor Day holiday about 1500 miles, 90% turnpike/expressway driving 60-70 mph, 10% city driving. Truck had 4 passengers, box full of luggage/cargo. I averaged 19.8 mpg hand calculated, DIC said 19.7 mpg average. I'm am running Kennedy's economy tune from the Rendezvous. And also running LT265 tires, speedo is accurate (verified with GPS). Had lots of driving in the rain and wind!!!!

[rob from bc canada]

This "economy tune" sounds real good.

I think mine would have done about 17 -17.5 driving as you have described.

If true, at $3.00 per Gallon, you saved about $30 on this trip, and if you keep the truck for 200k you might save about $4000.

From what I saw on Kennedy's site, you need a spare ECM to load his tunes.

What was the procedure for you, and what did the whole thing cost???

[ToddMeister]

This "economy tune" sounds real good.

I think mine would have done about 17 -17.5 driving as you have described.

If true, at $3.00 per Gallon, you saved about $30 on this trip, and if you keep the truck for 200k you might save about $4000.

From what I saw on Kennedy's site, you need a spare ECM to load his tunes.

What was the procedure for you, and what did the whole thing cost???

Check with John Kennedy for current pricing.

There is an article currently on the site that shows how to change the ECM.

Here is link to the article:

http://www.thedieselpage.com/reviews/jkecm2.htm