Thanks BBIC.

 

no problem...he's trying to fix a P2133 code that keeps coming up...he has kept me up to date very well via e-mail.

 

I'm wondering how ScanGauge gets around it. Must figure it differently. On three hundred mile trips the Scangauge is quite acurate. So there is a way, I suspect Edge will solve it soon.
Chris

 

Calculation of instantaneous MPG is pretty easy as long as the PCM can determine the fuel flow in gallons per hour (or some equivalent reading that can be converted to GPH). Just divide the current MPH by current GPH = instantaneous MPG.

As far as converting the instantaneous MPG into an average MPG, there are a couple of different methods. First, you could sample the instantaneous MPG at fairly short intervals (this improves accuracy), take the sum of the samples, then divide by the number of samples taken. Bill indicated in his e-mail above that the Edge was not dividing by the correct number of samples. If the counter is incorrect (i.e., if it is smaller than the actual number of samples), your average MPG value will be higher than the actual value.

Another method to perform the same average MPG calculation is to sample the GPH value, multiply each GPH sample by the sample interval (this tells you approximately how much fuel was used during the sample interval), and add this new value to a running total of the fuel used since the last reset. Then divide the total miles driven since the last reset by the total fuel used to obtain the average MPG.

I don't have any inside knowledge of the inner workings of the ScanGauge or the Edge, but these devices probably use some variant of the algorithms above.

 

The difference being that the ScanGauge trip gas mileage is very close to dead on.
The Edge is fantasy so far.
I do expect them to fix it soon though. They have been very responsive.
Chris

 

I'm sure the ScanGauge also doesn't have a problem with an incorrect sample counter (like the Edge currently has). It probably helps that the ScanGauge performs a reset each time you turn off the vehicle.

I've noticed that the Edge's average MPG value is very close to what I normally experience (that is, until the counter problem skews the reading). However, in my daily driving, it seems to take at least two or more days for the problem to recur. When it does, I just reset the device.

 

I loaded the update to mine and the avg is right on . , 18.2 mpg hwy. 80 miles... I imagine the way they calculate it is by taking the pulse width of the injector and multiply it times the nominal lbs/hr injector size and then factoring the incremental speed.. either way mine seems close to correct...

 

Mine isnt being divided by any number it has turned itself into an odometer.Isnt it supposed to ask you at start up if you want to reset the ampg? I turn my truck on and the edge goes straight the the gauge readout screen.

 

the first 4 or 5 times, the unit displays the disclaimers/warnings. You hit enter to accept, then it asks you if you want to reset.after the 4 or 5 times, it should go straight to the normal displays....

 

This would be a good way to determine the average MPG--it is similar to the second method I described above. (The difference being that the sample interval is variable and the sample value is constant.) Cool idea. However, in BBIC_Strait's post above, it seems more likely that the Edge uses something similar to the first method I described. To quote Bill's e-mail, "...we were not dividing by the correct number of samples."

If the counter Bill mentioned above isn't updated, your average MPG will increase just as you've described. If you want to reset the average MPG, press and release the "Enter" button on the gauges screen. You will then be asked to confirm if you want to reset the average MPG reading. Press "Enter" again to confirm or "Menu" to cancel.

 

Sorry C-17, i posted basicallywhat you already said!! The impg is probably calculated using the gph/pulsewidth calculations like we said. But the ampg is an running avg of those impg taken with respect to time.... I could be wrong though!!!

 

Did you guys download to the latest firm/calib verison; 13 and 15a???? I'm wondering if this will fix this problem. I believe my unit is w/i the range; I have the latest updates.

 

Bill just e-mailed me. He said they should have another update ready on Monday which should resolve the AMPG issue. Also, for those of you who have the TEGE2 hex code, they should have a fix for the P2133 DTC code on Monday also. (2006 4.6L)

 

...or maybe today

 

Maybe today?