Engine/Transmission (1998.5 - 2002) Mileage--has anyone really improved it?

[geusterman]

Y'all. After a phone conversation with Bill Heath, the Dieselmeister, (see TurboMaster ads on TDR), I may have an idea regarding what might be wrong. He asked me how it ran. I said it is a little "gravely" on acceleration (or "grainy") and he thought it should be as smooth as a baby's bottom and that maybe the VP44 was faulty. So one of these days I will go over to Ellensburg and take him up on his offer to drive it and see if it is funky as he drives them every day, stock and modified. George

 

[MrFixit]

Performance Curves

You guys might want to check issue 33 pg. 30. This is a great article about fuel consumption for the different cummins engines and the debates that go along with it.



Basically, the cummins performance charts are listed in this article. The highest mileage can be achieved at the engines lowest Brake Specific Fuel Consumption BSFC. For the 24v, the lowest number is at 2000 RPM. I usually run at this RPM and get 21 mpg easy hand calculated. If I slow it down a little, I do a little better. As others have said, 1300 rpm is way to low for the 24v. It does sound like you have other issues though.

Good luck with you problem and be sure to let us know.



Fixit

 

[JRodgers]

Is there any chance that these poor mileage symptoms could be caused by an injection pump that is slightly out of timing? The VP44 does have a timing adjustment. If it were off, would the result show up as "gravely" acceleration and poorer mileage? Comments?

 

[tbrudder]

Re: Performance Curves

Originally posted by MrFixit

Basically, the cummins performance charts are listed in this article. The highest mileage can be achieved at the engines lowest Brake Specific Fuel Consumption BSFC. For the 24v, the lowest number is at 2000 RPM.

MrFixit,



You're partially correct. The engine's lowest BSFC indicates the point where the engine operates most efficiently, but we have to factor a few more considerations in.



BSFC is in units of lbm/hp-hr. That's how many pounds of fuel per hour are required for each brake horsepower, and it's the horsepower term that makes the situation a bit more complicated.



Aerodynamic drag (i. e. 'wind resistance' ) on a vehicle will increase with the square of velocity--twice as fast, four times as much drag. As the horsepower required to maintain a speed is equal to the drag (and various resistances in the tires, driveline, etc. which may be linear--I'm an airplane guy, can't remember exactly) times the velocity, the horsepower required from the engine increases with the cube of velocity.



Basically, this means that going twice as fast will require eight times the power.



Now, back to that BSFC term. Once we know the aerodynamic performance of the vehicle, we can determine how much horsepower is required at any given speed (if anyone knows where to find this data, please let me know), but in general it's proportional to the HP = V^3 relation above. Knowing the driveline losses, we can get BHP from HP, and using the power curve, relate that to RPM. Using the BSFC chart, we can get the fuel consumption per horsepower, multiply it by the BHP value, and figure the fuel flow rate in pounds per hour, which we can convert to MPG.



Still with me?

Okay. My point here is that while the engine may operate a bit more efficiently at any given RPM, if it requires twice the horsepower to run at the speed related to that RPM value, MPG may suffer--It all depends on the shape of the BSFC curve. I'm pretty new here, so I don't have the issue with that chart, but I'm guessing it has a bowl shape--higher at either end, lower in the middle (around 2000, you say). If the curve is fairly flat, then the absolute lowest value doesn't factor in as much as the cube-of-the-velocity term. But if it's fairly steep, the best BSFC value may indeed determine the most efficient operation speed.



Sorry if this sounds nitpicky, but there are real issues with relating the efficiency of the powerplant to the efficiency of the vehicle (it's a lot easier (and more pronounced) in airplanes, as the wing lift comes into effect, and there's generally no transmission; there's a very defined velocity point for longest distance, as well as longest time aloft--not always the same). But the slower you go, the less power you need, and less fuel. I'm guessing the most efficient operation speed would be at 2000RPM in first gear. :-laf



--Ty

 

[jponder]

Re: Performance Curves

Originally posted by MrFixit

You guys might want to check issue 33 pg. 30. This is a great article about fuel consumption for the different cummins engines and the debates that go along with it.



Basically, the cummins performance charts are listed in this article. The highest mileage can be achieved at the engines lowest Brake Specific Fuel Consumption BSFC. For the 24v, the lowest number is at 2000 RPM. I usually run at this RPM and get 21 mpg easy hand calculated. If I slow it down a little, I do a little better. As others have said, 1300 rpm is way to low for the 24v. It does sound like you have other issues though.

Good luck with you problem and be sure to let us know.



Fixit

Totaly False. Your best mileage is not going to come at the rpm where BSFC is lowest. People throw that out there all the time and dont think about what they are saying. That BSFC chart doesnt tell you the rpm of best mileage because there isnt one. Your best mileage will come in high gear at the lowest speed possible before you lug the engine.

 

[tbrudder]

Fuel flow gauge

It just occurred to me that a fuel flow gauge would make all this a lot less academic, and I'm wondering why I've never seen one of these on a car before--all the higher-performance airplanes (and I'm talking personal planes here, not bizjets) have 'em.



Some are mechanical (if not most)--the fuel supply line runs from the tanks through the gauge and then to the engine. I'd rather see an electrical remote unit, to keep fuel lines out of the cab, but they're functionally the same.



Basically, this would read in pounds of fuel per hour. Actually, probably in gallons per hour would be more useful for us (divide by 7. 1). Just divide your speed by this (could be automated), and you've got MPG.



And yes, I realize that this is probably exactly how the overhead computer calculates instantaneous MPG, but I've been told these aren't very accurate. I'd like to see an analog gauge or two (gal/hr and MPG) with a higher accuracy and update rate--I want to see the needle swing when I shift gears or put my foot in it.



Or perhaps a cruise control button for 'best MPG'. Wouldn't work so well with a manual, but with an auto, it could keep at the most efficient speed based on wind and terrain--might slow down too much going up a hill (and go waaaaaaay too fast on the way back down... ), but it would be interesting to see it implemented.



Just not enough innovation in gauges and display systems from the automakers, these days. Of course, I'm still waiting for my full-up Heads Up Display (with radar/sonar tracking, of course) that will give me real night vision; speed, velocity, and heading without looking away from the road; and put a reticle around the nearest vehicle, giving range, closing speed, and time-to-intercept, so my expectations might be a bit on the high side.



Maybe there's a reason I work in the aerospace field instead of the automotive one...



--Ty

 

[jponder]

Re: Fuel flow gauge

Originally posted by tbrudder

It just occurred to me that a fuel flow gauge would make all this a lot less academic, and I'm wondering why I've never seen one of these on a car before--all the higher-performance airplanes (and I'm talking personal planes here, not bizjets) have 'em.



Some are mechanical (if not most)--the fuel supply line runs from the tanks through the gauge and then to the engine. I'd rather see an electrical remote unit, to keep fuel lines out of the cab, but they're functionally the same.



Basically, this would read in pounds of fuel per hour. Actually, probably in gallons per hour would be more useful for us (divide by 7. 1). Just divide your speed by this (could be automated), and you've got MPG.



And yes, I realize that this is probably exactly how the overhead computer calculates instantaneous MPG, but I've been told these aren't very accurate. I'd like to see an analog gauge or two (gal/hr and MPG) with a higher accuracy and update rate--I want to see the needle swing when I shift gears or put my foot in it.



Or perhaps a cruise control button for 'best MPG'. Wouldn't work so well with a manual, but with an auto, it could keep at the most efficient speed based on wind and terrain--might slow down too much going up a hill (and go waaaaaaay too fast on the way back down... ), but it would be interesting to see it implemented.



Just not enough innovation in gauges and display systems from the automakers, these days. Of course, I'm still waiting for my full-up Heads Up Display (with radar/sonar tracking, of course) that will give me real night vision; speed, velocity, and heading without looking away from the road; and put a reticle around the nearest vehicle, giving range, closing speed, and time-to-intercept, so my expectations might be a bit on the high side.



Maybe there's a reason I work in the aerospace field instead of the automotive one...



--Ty

Yes I have thought that also. You could just watch your consumption and do a litttle math with your speed and you could find whatever you were comfortable with. One problem is the fuel is lubing the pump and being returned to the tank so its a little more complex. You could have 2 gauges one going ang one coming back and take the difference

 

[tbrudder]

Re: Re: Fuel flow gauge

Originally posted by jponder

Yes I have thought that also. You could just watch your consumption and do a litttle math with your speed and you could find whatever you were comfortable with. One problem is the fuel is lubing the pump and being returned to the tank so its a little more complex. You could have 2 gauges one going ang one coming back and take the difference

Now that I think about it, the electronics on the VP44 probably relate the fuel flow rate to the engine computer and PCM--this would need to be known to get the right amount of fuel for the conditions, anyway. I wonder if this is how the onboard computer gets its fueling rate to do the instant MPG...



If so, a better gauge/instrument with a higher update rate could take this signal from the fuel pump and do its own mpg or gal/hr figures with higher accuracy than the OEM computer. The common consumer finds gauges scary, I guess, hence the predominance of idiot lights on new cars.



--Ty

 

[MrFixit]

More factors

Yes curve was a bow shaped curve. It was late last night when I wrote and realized that I had not mentioned that other factors play into MPG equation. Although I have ran many tanks on my 01 at different RPM levels, I do see the highest MPG's around 2000 RPM (3. 54's). I try to use the same conditions (freeway, time of day, etc. ) when I calculate. So even though I throw the table out there, the 2000 rpm figure seems to work for my application.

 

[jponder]

Re: More factors

Originally posted by MrFixit

Yes curve was a bow shaped curve. It was late last night when I wrote and realized that I had not mentioned that other factors play into MPG equation. Although I have ran many tanks on my 01 at different RPM levels, I do see the highest MPG's around 2000 RPM (3. 54's). I try to use the same conditions (freeway, time of day, etc. ) when I calculate. So even though I throw the table out there, the 2000 rpm figure seems to work for my application.

Why are you spewing this misinformation on here. I will bet you 1000$ that 2000 rpm is not your best mileage RPM. that is a load of BS. I've got 10 $100 bills that say you are mistaken. You drive one way at your magical 2000, sweet spot, rpm that engine likes, or any other names people try to associate with the charts and I'll show you real fast you are wrong. You risk 0 I risk 1K what say YOU?

 

[Hohn]

The only problem I can see with the flowmeter installation is that it tells you how much fuel goes to the engine-- NOT how much is being burned. Remember that our trucks take in a lot of surplus fuel used for cooling and lubrication.



It is HIGHLY improbable that the decrease in BSFC at 2000 rpm offsets that HUGE increase in drag as you go faster. Remember, BFSC is in tiny amounts, and if it decreases from, say . 510 @ 1700 RPM to, say, . 490 @ 2000 RPM, then this is not that big a difference.



However, the difference in power required to maintain a certain constant speed (road horsepower) goes WAY up from 60 mph to 70 mph, which represents the approximate increase from 1700 to 2000 RPM.



The bottom line is that a small decrease in BSFC is GREATLY offset by the large increase in road horsepower, thus you WILL have lower mileage. There's nothing academic about it-- it's fact.



Anyone may get decent mileage at 70 mph, but that samer person WILL get better mileage at 60 MPH.



If I had a stack of bills like jponder, I would levy the same bet... .



HOHN

 

[MrFixit]

No need to be harsh!

I am not trying to misinform anyone and I don't bet. I am mereley reporting what I find with my truck and what I read in TDR magazine. I had said "AROUND" 2000, vs. 1300. I did say ealier that if I slowed down a little (65mph vs. 70mph@2000rpm) that the mileage was a little better. If it is different for you, so be it. You guys are beginning to sound like the Ford Forums now. Don't go after me, go after those who publish in TDR. I am finding out like others have said, you can't debate the MPG issue. Enough said.

 

[Hohn]

Agreed-- civility needs to be maintained. My apology if I came off as less than civil. .



JLH

 

[jponder]

Re: No need to be harsh!

Originally posted by MrFixit

I am not trying to misinform anyone and I don't bet. I am merley reporing what I find with my truck and what I read in TDR magazine. I had said "AROUND" 2000, vs. 1300. I did say ealier that if I slowed down a little (65mph vs. 70mph@2000rpm) that the mileage was a little better. If it is different for you, so be it. You guys are beginning to sound like the Ford Forums now. Don't go after me, go after those who publish in TDR. I am finding out like others have said, you can't debate the MPG issue. Enough said.

I apologize and I sent you a PM but I think the things that you are saying about the charts dont have a D$mn thing to do with mileage. I wasnt trying to bet, I was offering you 1K if I was wrong with you risking Nothing. The charts you are talking about have 0, nothing, to do with max mileage and i am sorry but it is a pet peeve of mine to hear people use those charts or the dreaded "SWEET SPOT" The dreaded sweet spot kills me more than anything. It is generalizations ad misinformation plain and simple and It just bothers me. I didnt realize that you were in Ca so I rescind my 1K offer cause thats too far to drive. Less you want to come here and cash in

 

[jponder]

Originally posted by Hohn

Agreed-- civility needs to be maintained. My apology if I came off as less than civil. .



JLH

I was bluffing

 

[geusterman]

Yes boys, civil tongues. No need to act like Liberals . I wonder if there is a VP44 test that would "hook in" after the pump and before injectors (so engine could run) that would show just what the pump is doing. Anybody? Or is there a VP44 test I just have not heard about? George

 

[MrFixit]

No Worries

No problems guys. Maybe I should take you up and drive to Georgia. I could sure use a vacation and I would surely use quite a few tanks of Fuel on the way there

The PM seemed to be a link to this site.

Take it easy

Ramon

 

[jponder]

Re: No Worries

Originally posted by MrFixit

No problems guys. Maybe I should take you up and drive to Georgia. I could sure use a vacation and I would surely use quite a few tanks of Fuel on the way there

The PM seemed to be a link to this site.

Take it easy

Ramon

Come on down. I'll hook a throttle cable up on that truck and slow those rpms down to 1600 and bang out a 25 MPG run for ya

 

[slo-ryde]

I have the HO/6speed combo too. Haven't towed anything yet but my worst mileage on a tank since taking delivery was just slightly under 18 miles to the gallon. That was a lot of around town and having fun winding out the gears to 3 grand (it was a break-in thing).



I don't know much about how everything on this motor works but 14 mpg seems low.

 

[Wiredawg]

OK Rocket (or airplane) Scientists

I see our engineers and scientists are out in force on this subject. Well, I'm pretty low on the scientific totem pole so I'll give my two cents: I maintain a log of every tank of fuel I put in both of our trucks. I manually calculate mpg each tank. W/ 4. 10s in my dually, I run between 2,000 and 2500 RPMs all the time. I avg 15. 3 MPG. Truck weighs 10,100 lbs w/ all accessories and me. The main variable I have in my mileage is how aggresively I accelerate. My truck is BOMBed. I find I get the best mileage (not that I'm too worried about it) when I keep the EGTs down around 800 and boost 10 lbs or less.



I have 24,000 miles on my truck and it amazes me how I can drive it like I stole it and see slight (tenths mpg) increases along the way.



Here is the scientific formula for my results (the square of the force of my foot on the acelerator times the power level of my TST PM3 plus tailwind or minus headwind = FPM (Fun Per Mile)



Honestly though, this is an interesting post. Lets keep it coming.



Wiredawg