Why would more air reduce economy? As long as it doesn't increase fuel inlet it should stay about the same, i think. Thats my understanding of compression ignition anyway.

 

these trucks are boosting the way they are due to some sort of increased load.
but i agree with the op, boost on these kills mileage

 

This may be stupid but can you explain to me what DPF is?

 

Diesel Particulate Filter.

New emissions BS on the newer diesels (08).

 

gotcha....not gonna worry about it then.

 

This is interesting that this happening. I take it your in 6th gear when this happens? Whats the rpms like when this sudden jump in pressure. I have one other question when you removed the DPF does the exhaust system still do the automatic cleanse option? That is probably not what it is called but I heard that raw diesel fluid is squirted into the exhaust system to clean the exhaust or somehting of that nature (this is the same thing prompting the early recall from flames spewing out while in idle).

 

Yes I'm all the way in OverDrive gear, and I no longer have any form of a regeneration cycle left on my truck.

But some of you are understanding what I'm saying. More air needs more fuel resulting in less mileage. The boost response on these truck is awesome while your towing or in very hilly areas, and I've never had to down shift in my truck for a hill, the boost just shoots up. But it is very sensitive, any load it feels and here comes the power. I was getting 42 psi stock, and now with the DPF off and tuner I have gotten over 50 psi :icon_ford:

My whole idea is if it's possible to decrease the boost the truck produces while unloaded at highway speeds we should be able to get even better mileage.

 

I live in mass and encounter the common hilly terrain you associate with new england...

that being said...my truck rarely downshifts...it generally compensates on hills with BOOST...i can run flat around 5 psi...throw in one small hill suddenly im at 15-18 psi and fuel econ is dropping...god forbid you hit a long 5 or 6 percent grade, boost flys way over 25 psi (and fuel economy drops substantially).

All that time..truck will never downshift....im sure a down shift would drop fuel econ too, but just wonder which one is the lesser of the evils...

 

I live in mass and encounter the common hilly terrain you associate with new england...

that being said...my truck rarely downshifts...it generally compensates on hills with BOOST...i can run flat around 5 psi...throw in one small hill suddenly im at 15-18 psi and fuel econ is dropping...god forbid you hit a long 5 or 6 percent grade, boost flys way over 25 psi (and fuel economy drops substantially).

All that time..truck will never downshift....im sure a down shift would drop fuel econ too, but just wonder which one is the lesser of the evils...

This is what I was going to say.......yes when the truck senses the its losing any kind of speed and the pedal position is the same it will use the variable viens and increase boost, instead of down shifting or increasing RPMs, increasing boost is not only the most economic way to get more power, but it is less wear and tear on the motor and tranny......also South is right in the keeping the turbos below 10psi is the best way to see good MPG, buts not easy to do :nod:

 

Always remember to create boost you need to add fuel to spin the turbine, so anytime your boost is up you are providing more fuel, so your mileage will decrease:thumb:

 

with more boost you do add more air. more fuel is added too in response to the air flow through the maf. otherwise, you would run too lean.

 

Your RPMs stay consistent because in a given gear at a given speed your engine will be turning a specific RPM (discounting torque converter slippage). High boost correlates with any need for greater power, which is why boost is higher when you're towing.

When you're driving into the wind, you're effectively loading the truck just like if you were towing something. We've all seen the difference in fuel economy these trucks make at 70mph versus at 85mph, and the reason for that is that the force exerted on your truck is exponentially related to speed (something like speed to the 1.5th power). To go 60mph with a 15mph tailwind entails a drastically different power requirement than to go 60mph with a 15mph headwind.

For a simple experiment, hop on a bicycle and try to maintain 20mph into a headwind and again with a tailwind. After a few miles you'll see how much more tired you are going into the wind! You being tired on a bike is analogous to your truck drinking more fuel.

 

Great idea............something like Dodge and GM are doing when they drop 4 cylinders when cruising.

 

In my first post I said that even driving on flat roads without any wind at all the boost will level out anywhere between 7-12 psi. This results in a 6mpg difference between those two pressure driving the same flat road with no wind. Some days it will stay at 7psi and I'll get 23mpg, and others it will stay at 12psi and I'll get 17mpg. I always drive the same speed also, so there's no difference there.

I just think that if a custom tune could be made that would make the computer less sensitive to small loads, such as wind and light trailers, the boost could stay low and mpg's would increase.

 

Adding boost helps the fuel burn more, less smoke. This does not mean that more fuel is not added but if the same amount of fuel is used boost gets more out of it. If the vehicle smokes a lot it needs more boost. If it's running right more fuel is added when boost goes up. Otherwise the boost should have already been up to maximize fuel burn.

When you see the boost go up it is to get enough power to stay where your foot is. Let up and slow down and it will go down. It is a change in load that is causing it. Less turbo would make it use more fuel or it would decrease power.

We can see improved mpg if we slow down up hill and sped up down hill. This is not usually practical and so I just let it Gnaw.

I have also been with a high wind for quite a few miles and saw 22.8 mpg. This is like having a lighter truck, going slower, or going down hill.

Air pressure is exponential. If you double your speed the air forces are increases by eight fold. Weight is one to one. Double the weight and it takes twice the power.

Also when the wind is blowing a twenty mph wind has eight times the power of a ten mph wind.


On another observation I filled up a few days ago and my mpg towing sucked. 8.5 mpg.

I have been seeing 10.5 to 12. I think the trucks don't like some diesel as much as others. It's also possible I have added more weight to my camper than I thought.

 

Hopefully this clears up some confusion. I've seen a lot of people on here that say the increased boost lowers fuel economy. Wrong. More fuel reduces fuel economy. Here is the best way to explain it. Added fuel is not caused by higher boost, actually higher boost is caused by added fuel.

Ill throw some #'s out there, im sure they are WAY off, but its for example. Lets say you are cruising on a flat road at 65 MPH. Your boost is at 5 PSI and you are injecting 10 CCs of fuel per injection. You come up on a hill, your boost climbs to 10, and now you are injecting 25 CCs of fuel per injection. That is why your econ goes down.

Now, same numbers, different scenario. What some of you seem to think is that if you are goin 65 at 5 PSI and 10 CC/injection, that if you reduce the boost to say 2 PSI, you will get better econ. Actually that would make the econ worse. Ya guys follow what im sayin?

Higher boost is the by product of more fuel burned.

 

so what would happen if the engine was naturally aspirated or close to it at 65 mph?

 

ya mean like no boost at all? If its doing it on its own then you are prolly gettin good fuel mileage because you arent burnin much fuel.

 

economy

I kind of see what southdiesel is getting at....If someone can tune the trucks to get 500hp which is overkill why can't we tune it the otherway....truck has less power sure but only making enough to get and keep you going.....now maybe it doesn't work that way I dunno....I know there has to be a happy medium somewhere where tunes waste fuel for super hp and tq and where the truck is making enough torque and hp to keep it going without having to really squeeze as much juice ...I know there is no fantasy world where they run on no fuel....but this is why the minds at be are supposed to be experimenting on "economy tunes"

 

I think you are onto something...reminds me of an observation I made early on with my 07 when it only had maybe 3000 miles on it:
If i stepped hard on it and gradually let off on a flat road at 65...the boost would settle to maybe 10lbs when I reach speed. If I then letoff totally ,then gradually reached speed again boost would be around 5 or barely deflected.The factory tuning of the vanes favors performance and fast turbo response. I make it point to decellarate for a few secs now.

 

Yeah, I think I understand what South Texas is saying as well, and what COB is saying also. Cob, are you considering that the 08 has a variable vane turbo feeding the 2nd turbo. I think what I'm saying is that boost and exhaust does not correlate equally because of the variable vane turbo can add or decrease the amount of boost independently of how much exhaust you are making. does this make sence or not or am I out in left field on this???

 

If there were no turbo there would be smoke under load due to unburned fuel. The unburned fuel is wasted, therefore economy goes down.

The turbo turns by the burning fuel and aids in burning the fuel by supplying more air. By reducing the fuel the turbo boost goes down. It's all controlled by your right foot.

:dunno:

 

Yes, but I'm just talking about a tune made solely for economy. No towing or major loads. Just to help with empty mileage.

 

What I hear SouthTexasDiesel suggesting (as phill1060 agrees I think) is a tune that would *derate* the engine -- so that it won’t produce as much power.

We all talk about tunes *adding* 75, or 125, or 200 rwhp. How about a tune that *substracted” 100 hp or so? The suggestion is that such a tune would give us improved fuel economy.

If you had this, then if towing up a hill, or at high speed into a wind, or something like that, instead of using the power that the engine is capable of, the tune would limit the horsepower, so that the truck acted as if it had a weaker engine ... not increase the boost as much, therefore not use as much fuel, therefore not have as much power, therefore not be able to maintain the speed it was doing before the load increased at that level of pedal depression ... and therefore (in all likelihood) slow down.

I think it would be kind of neat. You could use it when you wanted to save money. If you wanted the engine’s full power, you could switch tunes (on the fly I trust), and get the full potential back, at the cost of worse mileage.

Hey Matt, Mike, Eric ... any chance of a -100 tune? Or a -200 tune?

-Brian

 

Could you not just put a block of wood under the gas pedal?

Every truck is different depending on what your hauling, where your driving, conditions, tires, gears, etc, etc. If you had 1000 hp your not using it just going down the road at 60 mph.

It's all controlled by your foot. You have to get good at driving it efficiently. What you really need is some really accurate real time fuel metering.


Most tuners do have economy. Most people find it is not the best setting for maximum mpg on these trucks because of their size and weight.


Boost increases economy and is controlled by your right foot. The more you get on it and the more load there is the hotter the exhaust is and more power goes through the turbo. If the boost does not go up when fuel increases it does not burn. Then you get a lot of black smoke and loss of power for the same amount of fuel used. It would also clog the DPF.

If you remove the DPF it's a different truck. These trucks need to be fueled without over fueling the burn. If they dump more fuel and can't get enough heat to burn it the DPF will clog.

 

There's a big part of this that I think everyone's missing. Fuel economy is a measure of efficiency -- getting the most energy to your wheels for a given amount of fuel. That's not a simple question of less power = less fuel. Unless you're talking about putting in a different engine altogether, reducing the power of this particular engine would likely result in poorer fuel economy because it wouldn't allow the engine to operate at it's peak efficiency.

That efficiency is a matter of many aspects of the engine -- displacement, head design, intake and exhaust, etc. Just because you put less fuel through the injectors for every combustion cycle doesn't mean you'll automatically use less fuel to get from point A to point B, assuming you're making the trip at roughly the same speed. With less power you're going to have to turn more RPMs in a lower gear to be able to move a truck like this. Based on my understanding of diesels (and engines in general), there's a pretty narrow band in which you get max power for minimum fuel. With these engines, it's almost certainly at a higher power level than stock.

My old 7.3L Excursion is a perfect example -- I did NOTHING to the truck other than an aftermarket air filter (stock intake tube) and a tune and ended up increasing my fuel economy by 20%+. It seems reasonable that Ford would tune down that engine for a passenger vehicle to make for a more comfortable driving experience (lots of torque and tighter shifting isn't always comfy).

I can appreciate the exercise, but I think it's flawed logic.

 

Well looking at it from a more technical side. Your claiming that you have to much boost.. or Excess Air. This has a specific name of Lambda. Its a measure of how far off, the chemisty is between an real and ideal diesel engine, interms of combustion efficienties. Lambda is a ratio of Air Mass/(Fuel mass*Stoichiometric ratio which is 14.5). A Lambda>1is lean and Lambda<1 is rich. Lambda = 1 ... Equal burn of fuel and air. Not quite directly realted but it is responsible for autoignition and thus the formation of pollutents.

When your diesel sits there and idles it is very lean thus you can leave your truck running without any real decrease in fuel (as compared to a gasoline fueled truck) the lambda value for turbocharged trucks is something like lambda>10 at idle. To get the best efficiency, operating the truck in the peak torque region will yield the most efficient results, thus the most MPG(which happens to be at about 1800-2100 RPM given various gears and rear ends). The engine computers on these things are pretty good at figureing out base line mixtures of air/fuel. However, everyone knows that if you tune your truck(at least pre-DPF days) you typically get an increase in MPG. The reason being is that you increase the efficeny of the truck at a specfic RPM reagion and you get more overall power.

Since you experience an increase in boost, your next step is to look at the operating conditions. Perhaps the temp was warmer and thus air was not quite as dense, this wont have the impact(on boost) that your talking about. You said that on an given flat piece of road your get XX boost and now you’re getting 1.5*XX boost, the engine is wanting more air for a reason.

The new diesels are very concered with Lambda becuase it also deals with the amount of pollutants formed(as listed above), during combustion. Is not possible to get full Mixing at a ratio of 1:1 or Lambda = 1 in the enitre cylinder. Without going into massively more detail(than I already have) most of the EPA brain child engines(2008+) have localized zones, within the combustion region, that are very lean. This inturn results in less soot occurring during combustion. EGR compatability then rises and NOx emmission are reducded. Ding Ding.. Excess Air is needed to reduce pollutants.

Overall everything is dealing with engine computer management and the equivlant ICP on the new fords. Unless something earth shattering has happend I dont think SCT can tune the ICP(or equivlant) on the newer trucks. Being that the EPA is out to kill us, they may have some double reduant system that, even though you have "all" of the EPA crap turned off, there is a fail safe within the ICP to enure less soot and more EGR combabality. Since your using the SCT(or any tuning package) it may sense the increase in boost and begin to dump more fuel in, because its structured for power. This is just pure speciculation and international would be the only ones who could tell you(about my ICP and EPA theroy). Perhaps something is off kiltered in the tuning, that has only come to the surface now. The new engines are more finicky then older diesels... However, if this was the case, then there would be more cases like you. Then again the factors casueing this could be on the level of 1000's of various mechanical/internal/enviromental parameters and you just happen to fit the bill at various instances in time.





What happened.. I just blacked out.....

 

Good post :thumb:

I'm glad you picked up on the part when I said under same conditions I would be getting different boost levels. I just find that to be weird. Maybe it could be caused by the EGR on the truck because that is not turned off. I just have the DPF removed and all regeneration functions off.

But I'm no expert, that's exactly why I put this post up. To get information an opinions.

 

For you tech heads, have a read on this article, it a paper on Ford's EGR/VGT calculations: http://ghost.engin.umich.edu/vgt6c.pdf

This thread caught my attention since I'm somewhat upset at the MPG that the new trucks are getting versus their counterparts from just a few years ago. EGR has long been a paradigm and a paradox! EGR does work to lower NOx and various other things things the treehuggers don't like, but it comes at the cost of power and increased fuel usage. In short, EGR is recycling some of the exhaust gases back into the combustion process to re-burn the particulate that didn't completely burn the first time through.

The paradox is as follows:

• As you increase EGR percentages you decrease the proper fuel mixture in the combustion cycle, therefore you need to increase fuel to obtain the optimum Air/fuel ratio for a good powerful burn.
• As you increase the amount of fuel introduced you also increase the NOx that is being recycled (on an adaptive EGR such as found on the new 08-up).

This unfortunately does not scale equally, thus the paradox. Hopefully SCT comes out with programming to disable the entire EGR system. Then and only then will you see stellar MPG's.

 

Yeah that makes sense, good find.

 

Thanks, Sciulli, for a great post ... and Gahanna-6.4 for the PDF. This also addresses (in more technical detail than I could) a question I raised in an (the) other forum:

... there’s something I don’t understand ...

From all I know, smoke means combustion that isn’t complete. True of all fires and explosions. The most intense fires, with just the right mixture of air and fuel, and at the highest (most efficient) temperatures, burn intensely without any smoke or byproducts. Just white hot heat. No?

So if those piezo-injectors are really so precise, I would have thought that the very best tunes wouldn’t make any smoke at all -- if everything were working perfectly, if we were getting the absolute last ounce of energy out of our fuel.

(Plus, think about regen ... it’s burning the particulates out of the DPF, right? If they can be burnt out then, then there’s oxidation going on during regen, which theoretically could have happened in the cylinder, increasing power?)

But in actual fact the opposite is happening: these great new tunes are pouring out the smoke.

There’s obviously something I don’t understand ...

Bottom line: is smoke good?

(Me, I wouldn’t mind a stealth truck ... no sound, no smoke, just blow everything away. But like I said, that’s just me ... )

Thanks; I'm learning (slowly!)

 

Well, good question. Smoke that you see from diesel is a particulate, mostly carbon, which is returned safely to earth, yes its heavier than air! Carbon is a by-product of the diesel combustion process. In diesels, the more carbon(black smoke) you see exhausted, the more fuel you're burning. Look at the SuperStock and ProStock diesel pulling tractors. If you notice during their pulls typically when they're spooling up the turbo(s) you'll see a grey or whitish colored, ashey type of smoke, that is a lot of unburnt, raw fuel which quickly changes to a thick black smoke as the cylinder temperature pressure and heat increases and good combustion begins to occur. In diesels when you see black smoke its a good thing - for power anyway. Remember, diesel has a much higher carbon content AND the size of the hydrocarbon molecule is much larger than gasoline. If you see a gasoline engine smoking as much.. then something has gone horribly wrong

So, in short, and contrary to popular belief; black smoke from a diesel indicates its making decent power and that you have a good balance between air to fuel (for whatever fuel curve you're running) ratio.

Gray or white/lighter smoke is unburnt fuel that is being wasted out the exhaust, and is not good to see from a diesel.