Fuel_Economy calculated pid?

[Zeus]

Anyone know of something like this, or a way to do it? It seems like it would be super easy to divide vehicle speed by the amount of fuel being delivered (through injector pulse widths?). Alas I know nothing of programing Live so I'm wondering if anyone can help out.

I for one think it would be cool to have a gauge or graph that shows how your fuel economy varies based on tuning/hardware changes or driving habits.

[Blacky]

Tricky to do, because there is no PID (as far as I know) to retrieve actual fuel flow. There is a PID that returns injector pulse width in milliseconds but how to convert from pulse width to actual fuel flow (i.e. liters per hour, or gallons per hour) is not trivial. The conversion would need to be based on fuel pressure (not available on LS1) and injector characteristics.

Regards
Paul

[Zeus]

I guess if your VE table was dialed in so your BEN was right around 1 you could calculate it based on the VE, cylinder volume, and AFR couldn't you?

[joecar]

You can calculate approximate fuel consumption using airflow, AFR, VSS, density of fuel, and some imperial/metric conversions:

fuelflow (g/s) = airflow (g/s) / AFR

then use density of gasoline (petrol) (737.22 g/L found on web) to convert fuelflow to from g/s to L/s,
then convert to L/hour,
then convert to gallon/hour,
and then divide this into VSS (miles/hour), giving miles/gallon.

[Tordne]

You can calculate approximate fuel consumption using airflow, AFR, VSS, density of fuel, and some imperial/metric conversions:

fuelflow (g/s) = airflow (g/s) / AFR

then use density of gasoline (petrol) (737.22 g/L found on web) to convert fuelflow to from g/s to L/s,
then convert to L/hour,
then convert to gallon/hour,
and then divide this into VSS (miles/hour), giving miles/gallon.

There you go Paul, simple as that. So there will be a new calc PID in the next patch right

[ace68]

or you could just divide the miles driven by the gal used

[dc_justin]

Couldn't you also use GM.INJFLOW to get the injector flow rate, rather than using airflow (g/s) / AFR? Assuming you're not using a wideband, the AFR would only be commanded and not dead on, no?

[Blacky]

Couldn't you also use GM.INJFLOW to get the injector flow rate, rather than using airflow (g/s) / AFR? Assuming you're not using a wideband, the AFR would only be commanded and not dead on, no?

Riiiiiiiiiiiiiiight (in my best Dr Evil voice). Don't I feel stupid now. I had forgotten about that fuel flow PID

I'm sure the maths gurus among us can come up with a formula to convert {GM.INJFLOW} and {SAE.VSS} into a fuel economy value...

Regards
Paul

[dc_justin]

Riiiiiiiiiiiiiiight (in my best Dr Evil voice). Don't I feel stupid now. I had forgotten about that fuel flow PID

I'm sure the maths gurus among us can come up with a formula to convert {GM.INJFLOW} and {SAE.VSS} into a fuel economy value...

Regards
Paul

I created one that I am going to try on my drive home today to see if it works. Would be nice to see what the best combo for driving my T/A is for milage

{SAE.VSS}/({GM.INJFLOW}/737.22*3.785412)

Not sure if it is right, been a long time since I did "garbage problems" in high school physics, but I followed joecar's advice.

[Blacky]

One thing to remember when creating calculated PID expressions that use PIDs with both metric and imperial units, is to append the units to the PID name, like this:

If the speed is in mph and the flow is in pound per minute then use:
{SAE.VSS.mph}/({GM.INJFLOW.lbpm}/737.22*3.785412)

If the speed is in km/h and the flow is in grams per second then use:
{SAE.VSS.kph}/({GM.INJFLOW.gps}/737.22*3.785412)

Otherwise EFILive won't know which units to use when computing the expression.

The units are listed in
\Program Files\EFILive\V7\Configuration\sae_generic.txt
in the *UNITS section.
The first entry in the "Code" column is the one you need to append to the PID name.

Regards
Paul