Calculate MPG in real-time

[2kCivicSi]

I was thinking about making a tool that would compare RPM vs Spd vs Injector duration and plot it to statistically calculate MPG. Does this sound like crazy-talk or do you think I might get 'good' results from this method?

[greasemonkee]

This idea has always interested me for those who want to achieve optimum part throttle efficiency but don't have a constant load applying dyno at their disposal. To avoid BS maybe a formula based on inj duration and map only to be rated gallons/hour or possibly lbs/hour (if it were possible to estimate fuel density via iat?) - anything that would give a user definable timescale averaging accurate relative to itself whereas it would be possible to go down a certain road X miles long and produce a number in fuel consumed. I would pay money for something like this. After all, we are now in the age of fuel economy.

[calvin]

i have some formula's i just have to test it

[2kCivicSi]

My theory is this: There is a grid basically of injector duration vs manifold pressure (As the fuel pressure regulator is map-regulated) Then off this you have RPM vs Speed (Gear conversion) which gives you 5 linear scales for number of pulses per mile. If you combine the two and use some statistical formula on the results you should be able to quantify MPG based on the grid X 5 (one complete grid per gear).. basically something like a 10x20x5 3d matrix.. The hardest part is that to do it empirically you somehow need to correlate some sort of consumption figure vs your matrix where many variable is unknown.. (IE injector duration broken down into an opening + duration + closing time = liter/hour)

[Markcous]

I understand this thread is dead but I'd really like to know where this sits on the todo list for eCtune. Would be extremely useful right about now, thanks! (:

[2kCivicSi]

Nobody ever told me anything about doing this.. I came across someone who did it in hardware.. MPGuino, an Atmega168-based fuel consumption monitor http://store.fundamentallogic.com/ecom/ ... x&cPath=22 you can make it or buy it as a kit..

[Markcous]

Yeah I remember seeing that long ago, I just figured since Calvin can already do pretty much whatever he wants with the stock computer, making that feature available through datalogging would be a sinch since the ecu knows all and without extra hardware but meh, if I must, then I shall, MPGuino here I come. Thanks.

[mobyfab]

inj = injection time in milliseconds injsize = injectors size in CC kph = kilometers per hour.

Code: Select all

  //Duty cycle  duty = (rpm * inj) / 1200;    //minutes needed to travel 100km  hundredkm = ((3600 / kph) * 100) / 60;                         //fuel consumption in Liters per 100km  fuelc = (hundredkm * ((injsize / 100) * duty)) / 1000;                         //fuel consumption in Liters per hour (when car is slow/stopped)  fuelsc = (60 * ((injsize / 100) * duty)) / 1000;  

There you go. If you wish you can convert that to MPG of GPH These formulas are working on my microcontroller project