My DIC always has read less than my calculated numbers by 2-4 mpg.

 

The one time I compared it, my DIC was much higher than what I got. I think it said about 30, and I got 27 or so. I just always use my DIC. It's easier.

(God, I have a dirty mind.....)

 

I completed a 3400 mile road trip and my DIC was continually off. DIC 30.6, calculated 32.6,the last fill DIC 26.6, calculated 30.2. Does anyone know how DIC calculated mpg?

 

My dear wife takes the DIC as the gospel truth for mileage... and that gets my dander up. I try and tell her that what the DIC tells you, it only an estimate, and not actuall mileage!

 

As far as I know it is not an estimate but an average of all your driving. Set it to mileage and watch it change as you accelerate and brake, coast or climb a hill. It would not be what every liter or gallon used in your vehicle gets but an average of what they all get. As it is lower when you coast and higher when you accelerate the end number can not be what you actually got. Makes perfect sense to me. Same as the avg speed display.

 

I may be wrong but I think it works this way.

The engine has many sensors on it that take most of it's functions into account. MPH, RPM, Throttle Position, Gallons in the tank etc.

What it does is read all these items and gives you a estimate of the gas used.

Note though the fuel gage has a limit to read the full gallons and if you top off the tank you can get more fuel in it than the car will read. This can be seen when your fuel range does not move for a while after a fill up. This would account for extra fuel and for why some people see 1-2 more MPG than the DIC.

In short the only way to accuratly measure fuel use it to use a measued amount of fuel and drive it. Even if you so your own numbers who is to say you have put the exact same amount in the tank this time as you put in last time?

Most tanks can take one to two more gallons just in the filler nect alone. My Fiero can take about 2 because of the lenght of it and it is non measured gas.

You could also incorperate a flow meter to measure it that way but that is a bit over kill.

 

Since getting my 09 ls the first of July I have put 2989 miles on the car. I have created a spreadsheet that I enter all of my mileage into and the DIC and Hand calculated fuel economy balance out in the end. -- 32.13mpg --

I have had a variance ranginging from .04 all the way to 2.37mpg.
I estimate gallons used from the miles driven / DIC Economy to the actual gallons used. Over the long run it (as of today) I have a estimated variance of .02 gallons and .11mpg.

The most interesting that I had happen during this time is filling the tank with 16.7 gallons. Concidering that the car only has a 16.3 gallon tank it looks like I ran on vapors for a few miles. I actually think that I had another 20 miles that I could put on the odo before I ran out of vapor.

Kurt
09 LS

 

Your talking about the Instant MPG avg, so yes you are correct. But the OP was talking about the other MPG reading.