SGII, what inputs does it use to compute MPG?

[Backtobasics]

What information does the SGII use to extrapolate the instant MPG and average MPG numbers?

[Angmaar]

It uses the MAF (mass air flow sensor) in the intake and the VSS (for vehicle speed). By knowing how much air goes into the engine it can use a preset A/F ratio to figure out how much fuel is burnt.

[PaleMelanesian]

MAF (air flow) for some cars, MAP (air pressure) and rpm for others like mine.
It also needs the engine size.
It assumes 14.7:1 air-fuel ratio.

[cfg83]

Backtobasics -

This is what I think is going on :

http://ecomodder.com/forum/187883-post20.html

CarloSW2

[Backtobasics]

Originally Posted by PaleMelanesian

MAF (air flow) for some cars, MAP (air pressure) and rpm for others like mine.
It also needs the engine size.
It assumes 14.7:1 air-fuel ratio.

My truck is speed density, so no MAF. How does it use MAP and RPM to give FE numbers?

Originally Posted by cfg83

Backtobasics -

This is what I think is going on :

http://ecomodder.com/forum/187883-post20.html

CarloSW2

Regretably, that is too technical for me.

[Backtobasics]

I may be beating a dead horse. SGII asks me for engine size, but this is a hiccup. The truck was 5.2, but I swapped in a 5.9 a while back. EVERYTHING on the truck is still 5.2 based, but the block itself. 5.2 injectors, PCM programming, everything.

I use the SGII for instanteous driving feedback, more than anything. I have just learned about the tank fill up options where I can TUNE it completely to the truck, but I struggle to input the 5.9 when the PCM and injectors don't know it is 5.9 engine.

[PaleMelanesian]

Use the actual engine size.

Using engine size, rpm, and MAP, the SG can calculate how much oxygen is being pumped through the engine. (piston pumps per minute * cylinder displacement * air density)

Then, assuming it's fuel injected and uses closed-loop O2 sensor feedback, the fuel must be ~1/14.7 of the air volume for a clean burn.

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Really, though, calibration doesn't have to be ideal. If you improve your driving technique by 10%, you'll see a 10% improvement at the pump.
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[cfg83]

Backtobasics -

It's too technical for me too. I've read versions of similar algorithms over and over. Everything I did is based on this post :

Calculating MPG from VSS and MAF from OBD2

What I programmed is a lot of trial and error until I saw MPG behavior in the same range as the SG.

CarloSW2

[cfg83]

Backtobasics -

Originally Posted by Backtobasics

My truck is speed density, so no MAF. How does it use MAP and RPM to give FE numbers?

...

I think the SG is making a synthetic MAF :

IMAP = RPM * MAP / IAT
MAF = (IMAP/120)*(Volumetric_Efficiency/100)*(Engine_Displacement)*(MM)/(R)

Where :
- manifold absolute pressure (MAP) is in kPa
- intake air temp (IAT) is in degrees Kelvin
- R is 8.314 J/°K/mole (constant)
- The average molecular mass of air (MM) is 28.97 g/mole (constant)
Note that in the above formula, the Volumetric_Efficiency of the 
  (4-cycle!) engine is measured in percent 
Note that the Engine_Displacement is in liters.

In my opinion, there is an assumed Volumetric_Efficiency. When you do a fill-up and apply the correction factor, the correction factor modifies the Volumetric_Efficiency for your engine.

CarloSW2

[hummingbird]

Hey, one doubt here:

If MGuino MEASURES the injector pulses and integrates them, whereas SGII just 'guesses' about the fuel being used, I would expect MPGuino to be more accurate. Is this conclusion correct?

Also, what is the strategy the in-built FE meters in the new generation cars use? SGII one, or straight computation of fuel a-la MPGuino from the ECU itself?