Thread: How does Scanguage get mpg ?

uh..109 views and not 1 reply ??

OBD supplies instantaneous speed (distance/time) and fuel consumption (volume/time). Assuming the time is constant between the two (it is, equalling the update frequency of the OBD) the time elements can be eliminated, leaving distance and volume. MPG = distance/volume. Simple math...

Originally Posted by uncleal

..and fuel consumption (volume/time).

really ? And what is the PID for 'fuel consumption' ?

There isnt any PID for that. Scangauge use
0C - RPM
04 - Load
05 - Engine coolant temp
0B - MAP
0F - Intake air temp
To calculate MPG.

It must get pretty inaccurate when the AFR isn't whatever Scangauge is assuming. My Subaru runs ~14.7 most of the time (and I assume most cars do) but when it's on boost the AFR goes down near 10:1.

If it knows load, why does it need RPM and MAP?

Also, my Subaru has a factory MPG display that's based on injector pulse width, RPM, and MPH. I put in bigger fuel injectors and now it thinks I'm getting really great mileage. If there's an OBDII code for injector pulse width (IPW), and if you know what the flow rate and dead time (aka latency) is for your injectors, you could do it that way.

Originally Posted by mezz64

Perhaps it's because the information could have been found with a search? It wouldn't use specific codes, it would be too tedious to make it compatible with every OBDII vehicle and it can't use MAF because not every vehicle has it, which leaves the formulas in post #9 of that thread.

http://www.mp3car.com/vbulletin/engi...-maf-obd2.html

Using the equation in post 9 means they would have to know volumetric efficiency and engine displacement. SCII does not have that info.

I too have been wondering this. I have written several programs that use corporate PIDs for MAF and Odometer extraction, but I dont see how this works. I have hooked up an ELM327 and issued an ATMA to see what PIDs the SCII was requesting. SCII calls PIDs 0x0F,0x0B, 0x0C, 0X11,0X0D,0X05 AND 0X03 in a constant loop when it is installed in my 2008 Chrysler that does not support MAF.


I did find this site where it is claimed that all you need for a pseudo MAF is MAP/absolute temp.

http://www.omninerd.com/articles/Imp...uel_Efficiency

Originally Posted by mezz64

Perhaps it's because the information could have been found with a search? It wouldn't use specific codes, it would be too tedious to make it compatible with every OBDII vehicle and it can't use MAF because not every vehicle has it, which leaves the formulas in post #9 of that thread.

http://www.mp3car.com/vbulletin/engi...-maf-obd2.html

Using the equation in post 9 means they would have to know volumetric efficiency and engine displacement. SCII does not have that info.

I too have been wondering this. I have written several programs that use corporate PIDs for MAF and Odometer extraction, but I dont see how this works. I have hooked up an ELM327 and issued an ATMA to see what PIDs the SCII was requesting. SCII calls PIDs 0x0F,0x0B, 0x0C, 0X11,0X0D,0X05 AND 0X03 in a constant loop when it is installed in my 2008 Chrysler that does not support MAF.


I did find this site where it is claimed that all you need for a pseudo MAF is MAP/absolute temp.

http://www.omninerd.com/articles/Imp...uel_Efficiency