With diesel prices hovering about $3 / gallon I'm tearing back into my truck's ECM to extract more fuel economy. At this point I've done quite well, and run about 26-27mpg @55mph. My goal is to get over 30 at real driving speeds (say 65-70), although I think I've reached the point of diminishing returns.

A question to all who have been programing their truck for fuel economy.
What Strategy have you been using, and how successful was it?

I think this post should become a smelting pot of knowledge for all of those seeking to optimize their Duramax's fuel economy.

If your curious how to get your hands on my tune, I will post it once I've fine tuned it to the point I am certain it will not cause any engine damage. at this time I am not ready to make that claim, and therefore my tune is unavailable. After more instrumentation and experimentation hopefully there will be a "safe version" that I can release.

I'll start this off with one of my more successful strategy for fuel economy.

Coast Optimization
Basically I stated by recording a map of Fuel Economy vs Throttle base fuel rate and vehicle speed. I've attached two views of this data so please feel free to take a look.

There is a significant increase in the fuel economy in the coasting region, which is to be expected, but while driving it is difficult to get the vehicle into these regions without decelerating or in a "full coast" when the DFCO kicks in. My objective was to shift that steep region over slightly to the higher fueling rates, to get that dramatic increase when only coasting slightly, when maintaining speed down a low grade.

Basically from an engineering perspective it will take a certain amount of energy to move a vehicle at a certain speed, so to achieve my desired affect I would need to relieve the engine of other losses, reducing both it's power output and parasitic drag, to best make use of the potential energy stored from going up that hill.

I've played with timing and boost within that region, gaining about 2mpg overall, and more like 10-15 while coasting. Although the gain is nice, I had significant lag while transitioning from downhill to uphill, as well as some passing lag.

In summary this is an excellent way to cleanly gain mpg without creating and excessive pollution or durability problems. but this will hurt the responsiveness of the vehicle in transition from coast to power.

Thats pretty cool. I do have efi, but I'm still confused with it. I think itd be a great goal for someone to not worry about power and just try to keep stock power while making the truck more economical.

I think you're best way to gain fuel MPG is driving style. There may be a little to gain through tuning, but not much. Im not sure what you mean by "lean" tuning...there is no rich or lean on a diesel...its always running at stoich. The way a diesel works is that it ONLY uses as much fuel as is required for the commanded fuel rate (pedal position) and load. The only way you are going to keep it from using extra fuel is lower the fuel rate (dont drive as fast, use the cruise control) or lower the load (make the truck more aerodynamic).

So unless there is black smoke pouring out of your tailpipe, your engine is running "almost as efficently as physically possible". The reason IMO that everyone sees such a wide range of fuel MPG's is because everyone drives differently. When you are cruising in steady state in a perfectly controlled test zone (cruise control on, no wind, all tucks loaded equally, same mods), it doesnt matter whether you are running a 1004rwhp tune or a stock 300hp tune.....you're going to get the same MPG. The engine doesnt use the extra power and extra fuel of a performance tune unless your right foot tells it to.

Im not sure how you are seeing 27 mpg, and no offece, but I think 30mpg is a far off dream. You are still trying to push a 7000 pound brick through the air, and that takes a predetermined amount of hp and load. You are not going to change that variable unless you physically change the body of the truck.

The best I have gotten to date is around 21mpg. This is PURELY highway, cruise control set at 63-65mph. Highway ONLY, 7680lbs truck weight. But I hardly ever drive that way, so I generally get 17, maybe 18 mpg unloaded highway. Towing ~10,000 pounds I get maybe 11 or so on the highway.

just my oppinion..

ben

Are these real world numbers, (measured fuel vs. actual distance traveled) or data bus calculated (injection rate data vs. distance traveled data)? If you are talking the latter, anything you do to alter the programming is exaggerated (just a percentage), from actual gains.

Things to focus on are things already mentioned like driving habbits, air drag, mechanical drag etc. Additional gains can be extracted with the type fuel you burn (Biodiesel and or additives boosting the cetane). Tire selection plays a role too. Everything adds up. Keep us posted as to your findings.

I think you're best way to gain fuel MPG is driving style. There may be a little to gain through tuning, but not much. Im not sure what you mean by "lean" tuning...there is no rich or lean on a diesel...its always running at stoich. The way a diesel works is that it ONLY uses as much fuel as is required for the commanded fuel rate (pedal position) and load. The only way you are going to keep it from using extra fuel is lower the fuel rate (dont drive as fast, use the cruise control) or lower the load (make the truck more aerodynamic).

So unless there is black smoke pouring out of your tailpipe, your engine is running "almost as efficently as physically possible". The reason IMO that everyone sees such a wide range of fuel MPG's is because everyone drives differently. When you are cruising in steady state in a perfectly controlled test zone (cruise control on, no wind, all tucks loaded equally, same mods), it doesnt matter whether you are running a 1004rwhp tune or a stock 300hp tune.....you're going to get the same MPG. The engine doesnt use the extra power and extra fuel of a performance tune unless your right foot tells it to.

Im not sure how you are seeing 27 mpg, and no offece, but I think 30mpg is a far off dream. You are still trying to push a 7000 pound brick through the air, and that takes a predetermined amount of hp and load. You are not going to change that variable unless you physically change the body of the truck.

The best I have gotten to date is around 21mpg. This is PURELY highway, cruise control set at 63-65mph. Highway ONLY, 7680lbs truck weight. But I hardly ever drive that way, so I generally get 17, maybe 18 mpg unloaded highway. Towing ~10,000 pounds I get maybe 11 or so on the highway.

just my oppinion..

ben


I agreed 100% with you Ben. Those number are right on with what I am getting with the same speed. I do get 12-13 towing, but my load is less. :)

The fueling statement is true, a Diesel engine is fuel throttled, so more generally fuel in = power out. driving style is most certainly the easiest way to achieve better fuel consumption, but we all know that, and still can't keep our foot out of it.

My tuning improves fuel economy during non constant driving, more specifically the downhill kind. going back to [fuel in = power out] the actual statement should be [Fuel In] = Power To Ground] + [Power to Losses]. The losses section is the only one we can really modify. And I aggree about the brick statement, I have only been able to obtain significant fuel economy improvements in the 55mph range. 65+ and I'm pushing too much air, and never truly get the chance to coast. There are several losses I've been focusing on. 1) Air pumping losses, as in parasitic losses through the turbocharger. 2) compression losses, the energy it takes to reduce the volume of air. both of these are related to turbo tuning.

currently to increase the "steepness" of the graph, the off throttle region, I am actually running below atmospheric pressure, approximately -.7psi. This both reduces the drag through the turbo on the exhaust side, but also reduces the cylinder air density, allowing for easier compression.

I am now experimenting with timing and EGR during this area to see if I can use them to both preheat the charge, and further reduce compression losses.

If you were to read my PID while driving your would find that going up a slight grade on the highway I'm still getting 15~16mpg. and at absolute steady state only 22. but on the slightest downhill i'm now running at 30~35, and then it shoots off from there. so again, it does take a certain amount of fuel to move the vehicle and its losses at a certain speed, I'm just making use of the energy I put into the vehicle going up small hills, and being sure I can get the most out of it on the way down.

The fueling statement is true, a Diesel engine is fuel throttled, so more generally fuel in = power out. driving style is most certainly the easiest way to achieve better fuel consumption, but we all know that, and still can't keep our foot out of it.

My tuning improves fuel economy during non constant driving, more specifically the downhill kind. going back to [fuel in = power out] the actual statement should be [Fuel In] = Power To Ground] + [Power to Losses]. The losses section is the only one we can really modify. And I aggree about the brick statement, I have only been able to obtain significant fuel economy improvements in the 55mph range. 65+ and I'm pushing too much air, and never truly get the chance to coast. There are several losses I've been focusing on. 1) Air pumping losses, as in parasitic losses through the turbocharger. 2) compression losses, the energy it takes to reduce the volume of air. both of these are related to turbo tuning.

currently to increase the "steepness" of the graph, the off throttle region, I am actually running below atmospheric pressure, approximately -.7psi. This both reduces the drag through the turbo on the exhaust side, but also reduces the cylinder air density, allowing for easier compression.

I am now experimenting with timing and EGR during this area to see if I can use them to both preheat the charge, and further reduce compression losses.

If you were to read my PID while driving your would find that going up a slight grade on the highway I'm still getting 15~16mpg. and at absolute steady state only 22. but on the slightest downhill i'm now running at 30~35, and then it shoots off from there. so again, it does take a certain amount of fuel to move the vehicle and its losses at a certain speed, I'm just making use of the energy I put into the vehicle going up small hills, and being sure I can get the most out of it on the way down.

Unless you are running stock tuning, any 'calculated MPG' PID is innacurate. How are you getting negative atmospheric pressure. There is no vacuum on a diesel.

BTW when you are coasting downhill, even a stock duramax doesnt use any fuel. Its called DFCO ;)

but anyways, regardless this is a great project to work on, keep us updated with the results.

ben

well i calculate the fuel used, by the fuel flow rate. do a little math and it becomes gallons/hr. divide miles/hr by gallons/hr and you have miles/gallon. It's an instantaneous number, which I've been recording and plotting as you can see on my first post

Some people have had success with highway milage by cutting boost some at highway speed .... basically take the rpm range and fuel delivery that you reach when say driving 55-65 mph and reduce the amount of boost at that set of points .... you really don't need much boost at that point and you don't loose power at highway steady-state speeds. This will help with unloaded flat-level highway road mpg quite a bit.

I've been rather busy at work, and not able to keep this thread updated, but I will say that at the moment I have found some improvements with the pilot injection, although it is rather difficult to change it's parameters while keeping the smooth quiet demeanor of the stock tuning. The pilot is lost fuel with regards to power, as it contributes only a few hp.

has anyone had any success with altering the pilot injection?

I've been rather busy at work, and not able to keep this thread updated, but I will say that at the moment I have found some improvements with the pilot injection, although it is rather difficult to change it's parameters while keeping the smooth quiet demeanor of the stock tuning. The pilot is lost fuel with regards to power, as it contributes only a few hp.

has anyone had any success with altering the pilot injection?
Expanding lead time on the pilot injection will help a bit!

Hell ill take any kind of mpg tune. Ive never seen over 17. I even drove most of a tank on level ground and kep the motor under 2k with the cruise. average is 14.3. I run a (smoke like a 12v) tune and only lost .5 mpg Of coarse i have run 425 hard rwhp through my trukc for ever and never had any tranny problems. I think my truck has a mind of its own.

Expanding lead time on the pilot injection will help a bit!

How?