Fuel Used

[bad63lac]

I disagree. Your logic and math are off and I dont think you fully comprehend all the variables in this equation.

Anyway, I dont want to get into a debate but I am quite curious about some of your numbers from your test...


1) How are you getting 22.5MPG average on your way to work? (10 mile trip as you stated) Thats is higher than the laughable EPA estimates. I dont doubt that a completely stock truck can get ~21-22 on the highway (at 55, with cruise control on) but I do not believe at all, that your 10 mile trip to work, including all stop/go, city and/or possible highway speeds netted you 22.5 AVG MPG. Would love to be proved wrong.


2) So on your trip home (10 mile trip to work), you stopped at a light for 2 minutes and your AVG MPG dropped .5 gal? From 22.5MPG to 22.0? (Also, how are you 40 miles now when its a 20mile round trip?)


3) So I presume you also had some lights on the way to work? 22.5MPG? Hmm...



<--Certified math whiz/scientist/engineer (no really, I am)
<--Amateur internet flub debunker

 

[T-pole]

I disagree. Your logic and math are off and I dont think you fully comprehend all the variables in this equation.

Did you try what I suggested though?

To answer your questions,

1) Hybrid. I get anywhere from 17 to 26 MPGS (I posted about the 26 mpg day, it was a 50 mile round trip, but never went above 60 MPH, I think I even have a pic of the DIC, but anyways)

Also, if you're not to sure about hybrids, the engine doesn't shut off till everything gets nice and warm. My 10 mile trip to work does not meet that criteria during the winter, so the engine stays on. Thats another thing, if the truck used so little fuel when at idle, why did Chevy design the hybrid to turn off when coasting or idling?

2)I reset the MPGS on my way home the night before 30 miles + 10 miles to work = 40 miles, thought you were a math wiz:lol: j/k (all in good fun)

3) I did have some lights on the way to work, the 30 mile trip was mostly highway, getting me to 24, way to work had some lights, bringing the avg down. I was too tired on the way to work to watch the avg the whole way there, and honestly, it doesn't look like it from this thread, but it's not something I stare at constantly and obsess over. On my way home, I guess I was just more alert, and saw the AVG drop like crazy.

Alright, off to work to stare intently on my instrument cluster to stir up some more internet arguments:smilielol:

 

[bad63lac]

Did you try what I suggested though?

To answer your questions,

1) Hybrid.

That answered all my questions.


Now I just disagree with your knowledge of the GM hybrid platform and how it functions but I dont want to get into THAT argument. :smilielol:


Off to work as well...

 

[TN Tahoe]

30 miles is too much. You have to factor in that while driving a lot more fuel is being pushed through the injectors than when idle. A few minutes of idle wont affect it that much.


In any case, for sh!ts and giggles, I did the test and like I said, it does factor it in...


-Took a trip to the store last night
-On the way home reset my AVG MPG when I was 4 blocks from home
-Pulled in the driveway and my AVG MPG reading was 16.4
-Turned off the truck
-Remoted started twice (20 minutes idle)
-My AVG MPG was now 16.0



Again, the computer keeps track of how much fuel it delivers through the injectors. It does these calculations whenever the engine is running in order to provide the proper fuel mix. It does this whether you are driving, idle or remote started w/o the key in the ignition. It does not matter.

Good Info.. :thumbsup:

 

[T-pole]

Wow, I feel like a dork, and am by no means a math wiz, but check my math here.

your 16.4 MPG was from about 4 blocks, which usually equals about 1/2 a mile, right?

So;
.5 (miles) / 16.4 (avg) = .0304878048780487804878 (gal used)

.5 (miles) / 16.0 (avg) = .03125 (gal used)

20 min, used .0007621951219512195121 (the difference between the two)

0.0007621951219512195 gallon [US, liquid] = 0.58536585365 Teaspoon [US]
http://www.onlineconversion.com/volume.htm


I think your average dropped from 16.4 to 16.0 from fuel used on start up. Unless we really believe that a V8 burns 1/2 a teaspoon over 20 minutes at idle?

Please correct my math if I'm wrong.

 

[bad63lac]

4 blocks, half mile? Probably.

Teaspoons of gas? Mmm, tasty!


In all seriousness, the amount of fuel flowing through an injector (which is measured) varies. So for example, if your truck is idling, the computer is controlling the amount of fuel passing through the injector (and keeping track of this data, as previously mentioned). When you are driving, as you accelerate and RPM's increase, the amount of fuel being delivered also increases. It is not a linear increase. It is progressively increasing curve.

Due to the fact that as you drive you are sometime accelerating (at all different RPM's and fuel delivery ratios), you are sometimes coasting, sometimes idle, sometime in V4 mode vs V8 mode, this equation is far too complex to try to make any sense of by using simply basic math or averages.

It would require a complex analysis model which would involve knowing lots of data and metrics specifically about the engine/computer that neither one of us have access to.


I'm just trying to stress that there is no way for our measly brains to make any sense of the numbers we are seeing. The equation is VERY complex and there are MANY variables.



P.S. Maybe your fetsil valve is not capitulating enough and therefore you are seeing the difference in your gas usage.

 

[T-pole]

You still failed to answer my 2 questions though:

1) Did you try and drive 4 blocks again, and watch the AVG drop when you park/idle?

2) Is my math off?

MPG is simple - Distance traveled / fuel used.

You're way overthinking this by talking about RPM's and accelerating. My example was from your test of remote starting the truck. There isn't much RPM change, and there is NO accelerating.

You even admit, the truck keeps track of fuel used. That is the case whether you're at idle or WOT. Doesn't matter what the curve is, or what kind of masters degree you got in College. Distance traveled / fuel used = MPG.

This is really getting ridiculous. I wonder if gas gets expensive again, if we can by it by the teaspoon. :lol:

 

[bad63lac]

:duel:

No, I did not try your other test.


Here is some food for thought...


- Two Tahoes
- Both reset MPG
- Both drive .5 miles

- Driver A, accelerates to 30 mph, then coasts most of the remaining blocks
- Upon coming to a stop he's averaged 18 MPG
- Since he coasted most of the trip he's only used "x" amount of fuel

- Driver B, accelerates to 40mph and keeps his foot steadily on the accelerator until stopping
- Since he's a bit more agressive driver, he's used "x*10" amount of fuel
- His AVG MPG was 12 MPG


- Now they both remote start their trucks for 20 minutes
- For arguements sake, they idle at the exact same RPM
- The fuel delivered at idle per minute is exactly the same


Who's AVG MPG will change more? Who's may not change at all?



Answer:

Driver A will definitely see a change in MPG. He only used a small amount of gas so his idle time will definitely affect his overall numbers.

Driver B, even though driving the same distance, used a lot more fuel. His idling time may not have much (or any) effect on his AVG MPG due to the amount of fuel used at idle vs amount of fuel used during his trip.



This is in no way scientific or meant to provide realistic results with the examples I've given.

I am, again, just trying to point out that there are many variables to this equation which you happen to think can be ignored. During MY test, which I drove 4 blocks (actually 5-6 now that I think about it and probably closer to a mile) there was a mixture of a traffic light, 2 stop signs, some coasting down an incline, etc. My driving habits have a direct affect on the amount of fuel used.

The amount of fuel can vary very much based on all the examples I've posted in my previous responses. Given that its not constant rate of consumption, it is not so easy for you to make the generalizations and assumptions you've made.


I do agree that obviously your distance/fuel = mpg but it is hard to make comparisons or analysis by simple math.

Just hope you can accept this as food for thought...

 

[T-pole]

Just hope you can accept this as food for thought...

This is great!

I feel like I'm in school again and have a homework assignment.

You're right, A will change more. If we knew the final MPG after the 20 minutes, we could determine how much fuel was burned to bring the average down, since no more mileage was put on after the 1/2 mile runs.

But, if we assume that these trucks burned the 1/2 a teaspoon like I figured your truck did, we can find that:

Truck A MPG after 20 min was: 17.5192878

Truck B MPG after 20 min was: 11.7844311

Again, back to my point that 20 minutes would seem like it should burn more then 1/2 a teaspoon. And remote starting is not doing runs like you suggested. But even the differences between truck A and B, we can still figure out their fuel usage based on Mileage and MPG's

I blame all of this on DowntownDru for bringing up the idea that the computer might not average in the remote start fuel usage (which from what I've seen, I agree with! LOL)

This is all simple math based on the figures that the truck gives us. This is not "VERY complex with MANY variables."

 

[DownTownDru]

This is great!

I blame all of this on DowntownDru for bringing up the idea that the computer might not average in the remote start fuel usage (which from what I've seen, I agree with! LOL)

LOL... well, I stand by my observation that my truck doesn't track remote start idle in the DIC metrics. Maybe there is a TSB out there or a GM Tech lurking that might shed some light on whether or not GM's philosophy changed in the software programming sometime after mine was built.

Again, my girlfriend's 09 Malibu does count the remote start time... my 07 Tahoe does not. Is it a problem? I don't get as depressed looking at the average MPG the way things are working now =)

 

[T-pole]

Ok, so I did my own test today.

Reset my AVG MPG 1/2 mile from home.

Got home, and it was at 21MPG
after 1 min, 15.4 MPG
2 min, 12.2 MPG
3 min, 10.0 MPG

So, that proved to me how fast they will drop.

Then I did an auto start with the keys out for 2 min,

It dropped to 7.1 MPG when I put the key in.

Tried it again, for 2 min, and dropped again to 5.8 MPG.

So, I'll still argue my point that after 20 min, and 1/2 mile on the clock, it should drop much more then .4 MPG, (mine would've been at about 4 mpg after 20 min.

So, thanks for the math problems today, had fun:thumbsup:

 

[T-pole]

Lol, ok, so after the truck sat for about an hour, I tried the autostart for 5 min before heading out. MPGs remained at 5.8 No change. I give up for now.

 

[DownTownDru]

Lol, ok, so after the truck sat for about an hour, I tried the autostart for 5 min before heading out. MPGs remained at 5.8 No change. I give up for now.

Cuz the remote start fuel didn't count... :lol:

And I didn't ask you to do any math either :smilielol:

 

[T-pole]

And I didn't ask you to do any math either :smilielol:

LOL, but I like math! And I'm not even a math wiz/engineer, but again, these computations are too hard for a simple minded human.

So, from my little 7 min test, I found that after:
1 min, I used .009103 gal
2 min, was about .017619 gal
3 min, .026636
5 min, .047058
7 min, .062842 gal.

Math is fun:smilielol:

And, this morning, I let it run the full 10 min, got in, and there was no change in MPG's. I almost think that if you put the key in while it's in auto start, then it shows the fuel that was used, but if you turn off the car by the remote, or let it run it's 10 min, it will not keep track of it on the DIC.

Prove me and my simple high school education wrong bad63