Oh if it really was that simple


The computer isnt really determining mpg, its more like amount of work being done...Then translating that into fuel economy

Which requires more work? Empty-2000rpm, or towing-2000rpm? Given those, more work is being done while towing. Engine and vehicle speed being the same, but air and fuel consumption is increased....It takes more pedal to get there....More pedal means more fuel..And without air, that fuel cant be burned...Not knowing much much air is being consumed makes it difficult to determine how efficiently the fuel is being burned, whether the engine is rich or lean...

The amount of fuel injected is irrelevant if it's not being burned....Remember: unburned fuel counts against mpg....The computer could think your getting 30mpg, simply based on what is being pumped from the tank, but hand calc would tell you otherwise...(I know, that sort of backwards, but you get the point) Or a dead injector: its not putting out fuel, but your still going 70mph...same speed, less fuel used, must be good mileage, huh? Nope..Loss of power, other problems...But based on the above assumption, economy would be great......



Air consumption and fuel consumption, along with engine speed tells you how much work the engine is doing...Factor in vehicle speed and distance traveled, and you begin to figure mpg...



Why is it that this feature is availble on gas engines, but not diesels? I dunno, ask Dodge...This is merely what I've learned on the subject at hand



And sorry, hitting the reset doesnt work that way on '06's

 

Ok, using your example of towing vs running unloaded...

It takes more fuel to run a certain distance with a trailer hooked to the truck. Do you agree with me that the computer knows how much fuel is being injected? If you do not, why not?

I fail to see a problem with the computer calculating mileage when towing vs unloaded...if it knows the amount of fuel being injected, and it knows the distance traveled, it will certainly know that more fuel is being injected while towing than running unloaded. Is my logic correct here? If it is, then it should follow that the computer will display a lower mileage figure.

Similar to that, if fuel is being burned inefficiently for some reason, again, more fuel will be used to cover a given distance. Why would that present a problem in calculating mileage?


As a final note, please explain how the previous few model years of truck can display instantaneous mileage when you hit the reset button, but somehow inexplicably would present great difficulty in displaying an constantly updating instantaneous figure?

 

I think you've misunderstood me, or I have you...I understand you feel I have made it far too complicated....But I'm afraid you've made it far too simplified....

If I understand you correctly:
Quantity injected and distance traveled equal mpg

Thats great as long as all things remain constant, and the computer knows precisely what amount of fuel is injected during each event...You mentioned rail pressure and pulse width...But you left out nozzle diameter...Based on your assumption, the computer will see time and pressure...Time and pressure alone are insufficient to determine total discharged...Diameter is critical to the volume expelled...So what if an injector is clogged? Will it inject the same amount of fuel as a new one? Obviously not...But does the computer know the difference? I doubt it...

Remeber too, that we are talking about multiple computers working together

Pulse width is not a constant...Pulse width is adjusted constantly by the ECM...The PCM receives input from the O2 sensor, telling the PCM whether there is a rich or lean condition...The PCM relays this to the ECM, and the ECM adjusts injection events accordingly.......(This is an overly-simplified explanation of things...)

That is only one function....The PCM operates in 2 different modes: Open Loop and Closed Loop...the PCM and ECM together function differently given each mode....Dozens of sensors and conditions report to the PCM to maintain a balance between economy, power, and emissions...

I think it nearly impossible to calculate economy at the injector....Calculation should be done on overall consumption...To take all of that, all of the systems working together, and extrapolate them into instant mpg is quite complicated...So much infact, that my average mpg is normally calculated 3 mpg LOW...Hand calcs come out 1 to 5 mpg higher than the overhead every time....The overhead is a total SWAG......



Like I said above...The Cummins doesnt share many components with gassers...Though the principles are the same, they remain much different in fact and operation....I dont know why DC didnt give us instant eco, but I, for one, think its because of these things

 

Cummins may have already created the answer to your problem. This was in the last Cummins email newsletter. It looks like it's aimed at the fleet market, but if it's not priced as such, it may be an option.

Click this.....

I keep meaning to check it out at the local Cummins dealership, but I've been out of town working all month.. Web site doesn't have pricing info.

 

I may have been off mentioning that the 05's were the same as the 06's. but here is the scenario I am talking about.

On my 04.5, if I was sitting at a stoplight, not moving, in drive and reset the ECO AVG it would go to 0 (I am going nowhere and burning fuel).

On my 06, if I am sitting at the stoplight, not moving, in drive and reset the ECO AVG it will stay where its at, even when I hold it for 2 seconds. It resets the mileage and the hours function, and it is resetting the AVG ECO, it just works differently. The AVG ECO resets itself to the previous average and moves up/down from there, not the instant mpg at the time of reset that my 04.5 did.

I liked the way it worked on my 04.5, because it would give me what I would consider an instant mpg reading. If I reset it coasting down a hill to a stop it would read 40+ mpg. If I reset it at WOT it would read 1-3mpg.

There is a difference between the 04.5 and 06.

 

That's part of what I was talking about earlier-that's the instantaneous reading I mentioned. I'm gonna read the later responses to this much more closely tomorrow. Right now, it's late and I'm gonna drink some beer.

 

The company that makes the overhead display removed that feature. I forget where I was looking on the net, but I remember reading about it. However you can get one from a truck that does have it, I think 2002 has it. And maybe put it in an 05 or 06.

 

thats what we are looking for. Now the question is did they change the plugins or anything? Can I just replace my factory on with it?? I just called the dealership and got these numbers: part# 56045573AF list price $151.00, preferred price of $121.00.
Now he couldn't tell me what the functions were since he is just looking up the part but some research is involved. I personally woldn't mind spending $121. for something like this I have spent more on things that got me less in return. but I would like to see if it did work. I think we need to find an 02 diesel and see if it has instant mpg.

 

I've got the instant if I reset it every instant, not fun. I mentioned earlier that I just ordered a scan gauge that is supposed to do instant all the time. It's cost is 130 so if you can wait till Sat., I'll let you know if it works or not or you can push that button all the time.

 

mine has it....I just hit the reset button over and over and over while driving down the highway...

I like to do that to see how different terrain, wind, rpms, etc are affecting my mileage at that moment....gives me good idea of how to run her in future. I would set at one highway speed...hit reset...watch mileage climb. after it stopped......i would change speed and rpms...reset again. Did that over and over to find best speed for my truck...which appears to be around 1850 RPMs on the highway with no headwind on fairly flat ground....almost 19mpg. Since I hand compute not that big of a deal for it to be off a little for that tank. By end of tank it usually ends up being about where it was the tank before....15.3-15.7 for around town and in traffic during my daily commutes.

 

I've played with that on my mom's dmax. It's funny when it reads 1mpg.

 

They said that the scan gauge could be moved from vehicle to vehicle. I'll try it on my truck and van and then see if I can find a 05 or 6 to try it on.
Tree

 

Hey folks I have the instant read out on my 2000. I think that was the last year that it was done. It goes from 4 mpg to 99mpg depends how hard I stand on it, but it sure tell you how hard the engine is working.

 

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Thanks for the info "Irish4U". Where you able to find out whether or not I could just unplug my '05 overhead console and plug in this '02 overhead, and make it look and work fine?

Thanks for the part number "Underwoodtransp".

This is all good stuff, and this is more of what I was looking for. Although I must admit I did enjoy reading about all the other "how and why stuff" that "Herrin821" and a few others were able to focus on. All of this is good.

JZ




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Ok guy and gals. Got the gauge put on today. There is some set up to it. Program the motor size and size of fuel tank. Also it can be calibrated if its fuel mileage is off from had calculated. Instant is instant it jumps up and down as you shift or cost or speed up. It shows rpms, average mpg, trip mpg, water temp, voltage, throtle position, engine load, mph, intake air temp, MAP got mine up to 36.4psi., you can watch four different things at one time. I wish the fuel pressure worked but the ecm doesn't share that info.
It will take me a day or two to get it dialed in. I don't see any reason why it wouldn't work on any computerized diesel. There was something else that didn't work that I wished would, can't place it now. Once you get it set up for your vehicle you can save the setting so if you disconect there not lost. If you take it to a diffent vehicle you'll have to set it up for that vehicle. And then monitor the hand calculated miles in comparison and adjust it so its correct.
I'll keep you informed.
Tree DR