calc.ve .pid wrong?

[SSpdDmon]

There's a calc pid in the scanner I just noticed that computes a VE value based on MAF. The equation shows:

VEpcm=MAF*(IAT+273.15)/((displacement()*61.024)*RPM*MAP)*6155274.24

I didn't get any values that made sense with that and I wasn't sure how to represent displacement.

So, I tried the following:

VEpcm=(MAF*(IAT+273.15)*6155274.24)/(displacement*61.024*RPM*MAP)

...using cylinder_volume*8=5665.527336 for displacement and metric values for MAF, IAT, and MAP.

The result appears to be relatively close to my VE in grams*K/kPa.

Is it possible this calculated pid's equation is wrong in the EFI Live sae_generic.txt file?

[joecar]

Jeff, I pm'd Paul.

[johnsZ06]

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[Blacky]

The value of the displacement() function is determined by the displacement setting in the log file.

You can view/change the displacement setting in the log file here:
Edit->Log file information...->Vehicle Options->Engine:
Select from the list, or just type in the displacemnt in CC.

You can set the default displacement for a particular VIN in the customer details. The customer details are copied into a log file when it is recorded.

Regards
Paul

[mnotx]

I have done just that and still can't get the VE to work on old logged data(V1). Do I have to log new VE data before it will work?

[joecar]

Posts #4 and #5 don't follow on from post #1...

[SSpdDmon]

Displacement seems to not be a problem anymore....at least not for me (edited my sae_generic.txt file to always use 5665.527336). I don't log any other cars and don't plan on a stroker anytime soon.

The problem was the constant I highlighted in red. As it sits in the original sae_generic.txt, it's on the denominator side of the equation. When I moved it to the numerator side, the values started to look sane. After that and setting the displacement, the pid started working.

Without the displacement in the equation, I would get an invalid error because of "divide by zero" was a possibility.

[Blacky]

The problem was the constant I highlighted in red. As it sits in the original sae_generic.txt, it's on the denominator side of the equation. When I moved it to the numerator side, the values started to look sane.

No, the constant in red is on the numerator side - look carefully at the braces.

Regards
Paul

[Blacky]

I have done just that and still can't get the VE to work on old logged data(V1). Do I have to log new VE data before it will work?

No, once you update the displacement value in the log file (and replot the charts), then the calculated PID's value should reflect the new displacement.

Just to check the displacment is being picked up correctly, create a calculated PID with just "displacement()" as the expression. That should be a straight line at the value of the displacement.

Regards
Paul

[Blacky]

No, the constant in red is on the numerator side - look carefully at the braces.
Regards
Paul

Just to clarify,

a/b*c is NOT the same as a/(b*c)
a/b*c IS the same as (a*c)/b

Regards
Paul