Dic Fuel Usage

[Ben Bassinger]

So, I'm on my 3rd full tank of gas and decided to check the DIC avg gas mileage and fuel usage to my fillup. I filled up with 22.4 gallons and the DIC said fuel usage 20.9. Do you think the DIC is wrong, or am I getting screwed at that gas station? The mpg on the DIC matched the fuel usage from the DIC, but obviously using the fuel pump the gas mileage is considerably lower. Anyone else have this problem? And yes, I did make sure that everything was reset to 0 at the last fillup.

[PhilB]

I have noticed on my truck that the DIC fuel usage may be off up to .5 gallons when a full tank has been used. For example, the DIC may say I used 20.5 gallons, and I put in 21 gallons. I have 11k miles on my truck and I have noticed to be fairly constant.

 

I gas up at the same station and try to use the same pumps. I make sure the truck is leaning the same way if the gas station lot is sloped. I put in approx the same amount of gas when the nozzle clicks off, except with the newer nozzles it is really irritating to having it click off more often. The fuel difference will be less if I go less than 300 miles. On my pre-AFM trucks, the DIC was fairly accurate with the fuel consumed. I suspect it has something to do with the engine doing its AFM thing and the computer not counting the fuel correctly.

[VMax2007]

I'll trust the accuracy of my truck's computer over the accuracy of any fuel pump anyday!!! Think about it for a second. Your truck is capable of delivering extremely precise amounts of fuel through your injectors in very small volume rates, enabling your truck to run perfectly. A gas station fuel pump delivers several gallons/minute at a precision only good enough to get a proper dollar value applied to it. Which do you think is going to be more precise, a meter than measures in gallons, or one that measures in minute, computer controlled amounts necessay in today's high-tech engines? The DIC get's it's info from the same computer that regulates fuel delivery. Even using the same pump at the same station does not guarantee that it will "click off" at precisely the same fuel level in your tank every time.

[Roofer]

I'm sure there is more money spent in technology and specifics on that gas pump than on the DIC in a pickup. I wouldn't worry about that.

 

There are alot of variables also for gasoline, but the pumps are normally dead on. I fill up small jugs regularly and never noticed anything wrong with the pumps.

[VMax2007]

I'm sure there is more money spent in technology and specifics on that gas pump than on the DIC in a pickup. I wouldn't worry about that.

 

There are alot of variables also for gasoline, but the pumps are normally dead on. I fill up small jugs regularly and never noticed anything wrong with the pumps.

 

 

Where do you think the DIC get's it's fuel usage info from?

 

Of course you won't see discrepancies when filling up small jugs, but when you fill up a 26+ gallon tank and are depending on when it "clicks" off, then I put my money on the truck's info. Now, I'd like to see a comparison done where you fill it up to the filler neck until it overflows, then you KNOW the exact same amount got put in. That is HIGHLY not recommended though since you need room for vapor in your tank or you could backflow liquid fuel into your vapor rcovery system.

[jnpaddison]

the 'state seal' on the gas pumps implies a measured gallon is a pumped gallon ,,,

[VMax2007]

the 'state seal' on the gas pumps implies a measured gallon is a pumped gallon ,,,

 

Please elaborate...does it state any tolerances?

 

Again, I suspect variances in the "shut-off" point as the biggest culprit.

[slomo007]

The pump is more accurate. GM won't get fined if it's wrong....the gas station can and will.

[VMax2007]

The pump is more accurate. GM won't get fined if it's wrong....the gas station can and will.

 

The gas station will only get fined if the pumps are out of their specified tolerance zone (incorrectly calibrated). If my truck is off, it wouldn't run very well or consistently now would it? And would a gas station get fined if the auto shut-off point varies? Read my first post and think about it for a minute.

 

Not to sound like a know-it-all, but I am an Engineer and I can tell you for certain that flow-rate accuracies get worse with higher flow rates. The gas pump flows at what...5-10 gallons per minute? Your injectors flow at a tiny fraction of that.

[AthensGaZO6]

The pump is more accurate. GM won't get fined if it's wrong....the gas station can and will.

 

The gas station will only get fined if the pumps are out of their specified tolerance zone (incorrectly calibrated). If my truck is off, it wouldn't run very well or consistently now would it? And would a gas station get fined if the auto shut-off point varies? Read my first post and think about it for a minute.

 

 

 

I notice that when I am traveling and use a whole tank while on the interstate that the usage gauge is almost dead on. When driving around town it may be off as much as half to a whole gallon.

[tobias]

Here's some good information on the subject: http://www.caranddriver.com/reviews/hot_li..._police_feature

 

This only speaks directly to Michigan's procedures at the pump but it gives a good idea of how the pumps are scrutinized.

 

Daddy

[d3athsong]

I know around here, pumps are calibrated to 20L at either 15 or 20 degrees C depending on the station. So at different temparatures and over 20L, I wouldnt rely on what the pump tells you. Then again, i wouldnt put too much faith in Your dic either.

[Bostonsfavson]

I've found the discrepancy between the DIC and fuel pumps to be around one half gallon or so, with the DIC consistently indicating the lower number.

[Zembonez]

I don't want to enter into the whole "is the pump ripping me off" argument.

 

The DIC on my truck normally is within a tenth or two of the mileage I figure at the pump.

 

One thing to keep in mind... the DIC is offering an average fuel economy over the period from the last reset point to now. Resetting it at a fillup isn't necessarily going to give accurate readings. You need to let it average the figure over a thousand or so miles to get really accurate figures. I find that mine is very accurate that way.

[VMax2007]

I don't want to enter into the whole "is the pump ripping me off" argument.

 

The DIC on my truck normally is within a tenth or two of the mileage I figure at the pump.

 

One thing to keep in mind... the DIC is offering an average fuel economy over the period from the last reset point to now. Resetting it at a fillup isn't necessarily going to give accurate readings. You need to let it average the figure over a thousand or so miles to get really accurate figures. I find that mine is very accurate that way.

 

Jim,

 

This discussion is more about the "fuel used" reading on the DIC rather than the average MPG.