hello everyone!

this question is directed to the electricity nuts in the forum. on the overhead console, you are privy to such information as trip milage, mpg, current mpg, temp + direction, ect. now my question is about the mpg section. mpg is a simple equation. i know that the information for the milage is gathered off of the rear end but where does the computer gather the fuel consumption information? is it based off of throttle position? i put on 33" tires so i know that the information gathered off of the milage is incorrect right from the beginning. i am planning on correcting it with a superchips programmer. as far as fuel consumption, i am stumped. any info would be appreciated. thanks in advance!


chris

 

You know what, you still won't get accurate info on that OHC whether the pcm is properly programmed to your tire size or not. You'll have to do the math the old fashioned way when you get it reconfigured. I think the owners manual tells you how to reconfigure without a programmer? Can anyone tell me whether that's true or not. I don't remember if I saw it in there.

 

dodge, and several other manufacturers pulled the "instant MPG" feature from their vehicles because of exactly this. its calculated by the engine computer based on fuel consumption (measured by all vehicles equipped with OBDII) and vehicle speed. the problem happens because the computer calculates the average based on the assumption that at that given second in time that all the variables (speed and fuel consumption) will remain the same for the duration of the trip and it calculates the average. now the next second the variables have likely changed and now you get a different reading and this continues causing your average to jump all over the place. in later model vehicles all of this data is still aquired in the same fashion but the display shows the average over a longer time so its more accurate

 

thanks kurby for the response. i do understand the method of calculation that is being used. i am just curious where the computer gets the fuel consumption information. unfortunately in my case speed and sitance are both factors affected by the increase in tire size to 33". i plan on getting the superchips programmer to correct this. i just want to know where the computer gets the fuel consumption number from.

 

You want the answer virused? The computer is fibbing ya'. It is pulling that number out of it's ***. LOL Seriously though if you are a granny driver it will be close to what you're actually getting but every time you get on it and drive hard the comp doesn't put this into the equation for some reason. I don't really even bother with it I'll look at it for a rough guesstimate on what I'm getting but that's all it is.

 

I have always assumed that fuel consumption is calculated by the PCM from looking at the pulse width of the injectors.
I don't know if thats true, but that would be about the only place to get it that I can think of.

 

I'd assume you'd also have to know the fuel pressure to be accurate. my overhead comp is so far of its useless... 3~4 mpg on the high side.