OBDII / OBD2 and MPG calculation

I have just "installed" a cheap OBDII WiFi unit that transmits Tacoma data to my iPhone. So far it looks promising.

My question is: How does the unit calculate MPG? Does the calculation use my speedometer/tire revolutions to figure this out?

Well, sort of a dumb question. It needs to know distance travelled... Where is it getting the consumption side of the equation? i.e. Where is the truck monitoring fuel spent?

I ask as my speedo needs calibration since I've thrown bigger shoes on the truck.

Screenshots are from the $12 DashCommand App. So far it seems very functional, if not a bit clunky in its design and display.

 

which OBD2 wifi unit do you have?

 

you get cc's/min of fuel consumption from OBD. Pair that with speed and you get MPG.

its not the best but its closeish.... i stopped using my BT OBD and spare phone for full time dash gauge.... i kept getting distracted etc and i have found mpgs are better if im not trying for the best on the gauge, but just driving nice.

 

It's a "PanLong Diagnostic Scanner" Wifi version. Model: PL-OBDWifi

$20 or so on Amazon...

 

This might be of interest to someone: http://www.sersc.org/journals/IJUNESST/vol4_no4/3.pdf

A study that used OBDII throttle position and RPM data to see how well it predicts/models actual fuel consumption (as calculated through the ECU on their test vehicle).




Abstract
This Paper proposed the estimation method of fuel consumption from vehicle information through OBD-II. We assumed RPM, TPS had a relationship with fuel consumption. We got the output as fuel-consumption from a vehicle RPM, TPS as input by using polynomial equations. We had modeling as quadric function and surface function with OBD-II data and fuel consumption data supported by automotive company in real. In order to verify the effectiveness of proposed method, 5 km road-test was performed. The results showed that the proposed method can estimate precisely the fuel consumption from vehicle multi-data. It was observed that the proposed models using instantaneous engine RPM, TPS and (RPM, TPS) can predict the fuel consumption quite well with the coefficient of determination were 76%, 88% and 71% respectively.

 

Okay, so the vehicle is measuring how much fuel is flowing by. Seems simple enough. I guess I should update my speedo, as I think my odometer is now missing 8% of the clicks! Perhaps this'll help with resale down the road...


Driving nice helps, but sometimes you can find sweet spots/optimal spots at highway speeds that only a display can tell you about. Although, for relaxation and your sanity it might be best to just drive with a lightfoot and call it a day.

 

I'm interested to see how it compares to my fill up/fuelly notes. On this short test drive it's registering 18mpg. About 2 mpg better than my usual average...

 

I have, and for a while used, Torque (android). It provided a couple different ways to calculate. I found it reasonably accurate (within a mpg or so) and you can learn something about driving like you have an egg under your throttle. It started out entertaining and then became annoying.

Have fun.

 

it estimates mpg based on injector pulse width which is something that can be polled via obd port

it is very rough estimate unless the app is programmed to know the exact engine type and size and the more details it has or can accept, the more accurate it will be