EVIC MPG miscalculations partially explained *

[colletjr]

I've read several things about this on here in the past, and noticed something in my car the other day and didn't recall seeing it earlier, so if this is already known, I apologize for the repost.

I've seen some posts that mention that the MPG numbers in the EVIC are off because the EVIC will make the number go down any time the ignition is on, even if the car isn't moving. I didn't believe DCX would be that stupid as to do something like that, and it's not true. If you stick your key in and turn on the accessory or ignition but don't start, the MPG number will not change.

But what DOES affect it, and I consider this a bug, is that if you use the feature where the accessory power will stay on after you had the engine running and then shut it off, then the MPG number DOES change during this time. I'm guessing that this is the behavior others have seen that led them to think the EVIC was always updating MPG.

And I noticed that if you use the EVIC diagnostic mode, the pages that show RPM, etc. don't change once you shut the car off, while it's holding accessory power on. It seems to be something of a limbo state -- it acts as though the sensor values are frozen in time at their last settings when you turned off the car, so it will act as though you're idling but not moving, and your MPG will drop. Seems like the EVIC thinks the car is still running. So IMO it's a bug.

Once you open the door, it really shuts down, and then if you turn accessory power on, it no longer updates the MPG.

In my case, I'm often driving to the bus stop to pick up my wife, where I sit and listen to the radio while I wait, so this means my EVIC MPG numbers end up reading low.

[joseph]

Good to know, I never relied on my evic mpg because I very often turn off the car to acc. to listen to the radio while waiting to pick up my wife from work, but now that I know this, I'll turn it off completey then go to acc.

[Todd RT]

Right on Brotha!

I also wonder how far back in time it's calculating from. Or should I say how many miles? Stoplights gotta screw it up too.

[rhodyhemi]

Thanks for the info colletjr. I recently posted about this and I have seen the MPG in the EVIC change when sitting listening to the radio waiting of rmy son to get out of football practice.

Why is there no "instantaneous" mode?

[mcinfantry]

Right on Brotha!

I also wonder how far back in time it's calculating from. Or should I say how many miles? Stoplights gotta screw it up too.

how is a stoplight screwing it up? ive idled hundreds of tanks of gas through a car. so my mpg was actually zero.

[Todd RT]

how is a stoplight screwing it up? ive idled hundreds of tanks of gas through a car. so my mpg was actually zero.

Hmmm... guess I need to think about this. But if you start the car, sit in the driveway and burn 5 gallons of gas without driving at all, EVIC should say 0 miles per gallon. Right?

Now if I put it in gear and drive 1 mile around the block, won't the average MPG be like 5.1 gallons for each mile driven? Which would be approx .2 MPG?

Will the EVIC show this? Or just average of when you were drivin'??

You're probably right!

[hawkxp]

Thanks for the info colletjr. I recently posted about this and I have seen the MPG in the EVIC change when sitting listening to the radio waiting of rmy son to get out of football practice.

Why is there no "instantaneous" mode?

I wish the instantaneous mode was there as well. Its on the ODB bus, but most manufactures dont show it, peobably didnt like having to answer questions like "why when I am going 5 MPH does it show 2 MPG..."

Scott

[Northern300]

To get the instantaneous just watch it and reset it and it will give you the proper economy after about a mile.

Works perfectly.

Mine 22MPG city / 29MPG highway.

[quarky42]

The behavior depends on what firmware is flashed on your car. There are different flashes for different problems.

Mine no longer "counts down" on the milage while turned off. On the other hand when I leave it on the Engine Temperature screen in diagnostics the temperature will update while the car is in Accessory timer... It doesn't update very fast and the temperature doesn't change very fast (Except for an initial spike after the engine stops and coolant stops.)