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Discussion Starter · #1 ·
I have only tested this a couple times, but have gotten the same results. I think I know why some people report having inaccurate DIC readings on mpg and others say it seems to be dead on.

I have found that it seems that the DIC does not start calculating time, mpg, etc until you shift out of park and start driving. So it seems the DIC shows your average MPG while driving and does not include any remote start gas usage.

So if you remote start, and or stop and put it in park and let it run, your manual calculation will include the gas usage during those times but the DIC will not consider that driving time and therefore not include that gas usage in its calculation.

I drive from MD to Ohio often, and it is about a 400 mile 1 way trip. I can do this in one tank and if I fill up to the neck, reset the DIC and make the drive, immediately fill up to the neck again and calculate manually, I find I get almost exactly the same result. (i.e. within .1 mpg)

Just something I noticed that may or may not be fact.
 

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Re: Theroy on inaccurate DIC.

The only way i get accurate m.p.g. is to reset it when on the highway after a couple of minutes of driving highway speeds.
 

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GAR said:
I drive from MD to Ohio often, and it is about a 400 mile 1 way trip. I can do this in one tank and if I fill up to the neck, reset the DIC and make the drive, immediately fill up to the neck again and calculate manually, I find I get almost exactly the same result. (i.e. within .1 mpg)

Just something I noticed that may or may not be fact.
Just curious, when you say you "fill up to the neck", how many shut off clicks on the nozzle is that, and is it always the same number?
 

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Discussion Starter · #4 ·
Snoguy said:
GAR said:
I drive from MD to Ohio often, and it is about a 400 mile 1 way trip. I can do this in one tank and if I fill up to the neck, reset the DIC and make the drive, immediately fill up to the neck again and calculate manually, I find I get almost exactly the same result. (i.e. within .1 mpg)

Just something I noticed that may or may not be fact.
Just curious, when you say you "fill up to the neck", how many shut off clicks on the nozzle is that, and is it always the same number?
First. I don't do this often as you really should stop filling on the first shut off click. I think this has something to do with the environment and ensuring that gas fumes don't get released.

But occasionally, when I want to accurately check mileage, I fill it all the way up. I continue to patiently add through multiple clicks and slowly bull the nozzle out to get more in. I fill it until gas is full up the neck and if I was to put any more in it would overflow and run out on the ground. Normally, this is 2-3 more gallons than when I get the first "click". So I am very sure that the gas is at the same level as I can literally see the gas in the neck when I put on the cap.

Don't do this without knowing that you are not supposed to do it. I have heard that this could hurt some type of gas recovery, but every time I have done this I got right out on the open road and the first few gallons are gone pretty quickly. I have never had a problem with this.

One thing I have for sure found is that the turn off click from pump to pump is very different. They can be off by up to a gallon depending on which pump you are at. So if you check your mileage by using the "click" then there is a good chance your accuracy is worse than the DIC.

I had a 1997 Grand Prix with a DIC and the mpg and gas used when driving was within .2% of my measurements every time I checked it. I personally think the DIC is very accurate and I know for my Acadia, it has been within .1 mpg each time I checked it.
 

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GAR said:
I have only tested this a couple times, but have gotten the same results. I think I know why some people report having inaccurate DIC readings on mpg and others say it seems to be dead on.

I have found that it seems that the DIC does not start calculating time, mpg, etc until you shift out of park and start driving. So it seems the DIC shows your average MPG while driving and does not include any remote start gas usage.

So if you remote start, and or stop and put it in park and let it run, your manual calculation will include the gas usage during those times but the DIC will not consider that driving time and therefore not include that gas usage in its calculation.

I drive from MD to Ohio often, and it is about a 400 mile 1 way trip. I can do this in one tank and if I fill up to the neck, reset the DIC and make the drive, immediately fill up to the neck again and calculate manually, I find I get almost exactly the same result. (i.e. within .1 mpg)

Just something I noticed that may or may not be fact.
This also assumes the gas pump readings are 100% accurate. Who knows how off they could be from station to station. The DIC mpg is usually close to my manual mpg calcs, so I assume it is working well.
 

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GAR said:
One thing I have for sure found is that the turn off click from pump to pump is very different. They can be off by up to a gallon depending on which pump you are at.
I have noticed this too and it also seems to depend on whether or not the nozzle has a vapor recovery system built in.
 

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It also depends on whether you have parked on a slight incline one time and then flat or slight decline the next while filling up. I try using the same pump at the same station and I get better results. If I change from one station to the other the pump area I end up using has a big slant away from the pump. I always get worse mpg when I fill up there. ;D
 

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My DIC takes into account idle times (remote start). I can get out of the Outlook and it will say 17.2mpg. If I remote start and get in a couple of minutes later it will say 16.9.
 

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Discussion Starter · #9 ·
If you DIC is working that way, then my observations may be wrong. I am just trying to figure out why some folks indicate that the DIC is not accurate and off by a couple mpg while I am experiencing the DIC as being accurate. My theory could very well be wrong. I will watch closely to see if perhaps I just full of it. :angel:
 

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My DIC has been very accurate, usually within .3 of my manual calculation. I have found it all depends on how much fuel the DIC thinks you have used. I fill all the way to the top to get the most accurate reading and have found that where I put in 16 gallons, the DIC thinks I used 15.3 (example) which explains the .3 difference. I am very satisfied with it.

My wifes Aura has a real time MPG in addition to the standard one. So while you can see what the MPG is for the tank, you can also read what you are getting at that moment. Cool, wish it was on the Lambda's.
 

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The DIC may actually be more accurate than the hand calculation method. However, having said that, it may be rather hard to prove, since on the surface the hand calculation method should be more accurate.

The hand calculation method suffers from the variable as to the amount of gasoline added each time, as well as the consistency of adding the gas. Some of these problems have been mentioned before, but I'll list several.
1-Different pumps/nozzles shut off inconsistently and/differently. Nozzle rate of flow seems to affect the shutoff point.
2-Vehicle not being level due to any pavement slope at the pump. If the fill side is higher it will take more gas than if fill side is lower.
3-Temperature effects, although I am not sure how big this factor may be.

Some of my conclusions:
1-Hand calculated average mpg needs to be calculated over a number of fill ups, unless you can use the same station/pump/ground slope every time.
2-The mpg for one fill up may or may not be very accurate. The average mpg for 5, 10 or 20 fill ups IMO would be much more accurate when using the hand calculation method. (Even better would be with the same traffic and weather conditions).
3-I take with a grain of salt reports of really good or really bad gas mileage based on one or two tanks.
4-Driving style and weather conditions make it very hard to compare mpg between different drivers.

I have not addressed mpg variability due to octane and ethanol, but these are subjects for a different thread and have previously been discussed.
 

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Discussion Starter · #12 ·
I agree that over time the hand calculation would be accurate. In the past I would keep track of every mile and every gallon for a couple years and that was accurate. With the Acadia, I am going to assume that my DIC will be at least consistent. (I hope that is right). I am not going to monitor it to know exactly what mpg I am getting, but will use it to see if there are any major changes that could indicate a problem. Although the computer will probably tell me something is wrong before the mpg drops significantly. (Or one would hope so)

Reality is that I don't really care what my exact mpg is as I know I will be driving it and it is what it is. I just hope that :beer: does not get too expensive. :drunk:
 
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