No "calculated load" even though its a standard PID?

Tuning discussion for all first generation Mazda RX-8 (2004-2008)
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beernose
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Joined: July 7th, 2021, 5:22 pm

No "calculated load" even though its a standard PID?

Post by beernose »

While logging today, I noticed that I have 'Absolute Load" as defined by OBD2 spec, but the Calculated Load is not available in the "All parameters" list.

I noticed it mentioned as available for other Mazda variants of VersaTune. Is this just an oversight in the RX8 version?
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Ugnius @ VersaTune
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Re: No "calculated load" even though its a standard PID?

Post by Ugnius @ VersaTune »

In which platform did you see that PID? I don't think we include it in any platform, because it is of limited usefulness and will become inaccurate as soon as you tune your engine. The ECU uses absolute load in all of its internal calculations.
beernose
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Joined: July 7th, 2021, 5:22 pm

Re: No "calculated load" even though its a standard PID?

Post by beernose »

I'm talking about the Series 1 RX-8.

But SAE standard PID definitions are for both Absolute and Calculated load. Yes, I'm aware that these vary according to the tune (and whether there's a turbo/supercharger), but they're used by the PCM to determine which point on the map to use for the target lambda. So seeing the reported load (especially 'calculated' while help us know which range of cells we should be tweaking in our map.

It lets me see: PCM saw XX g/s flow from the MAF, so after adjustments, that equals YY % calculated load (and then I can correlate the target lambda from there)

PID $04 = Calculated Load (Range from 0 to 1.0 representing 0% to 100%)

PID $43 = Absolute Load (Range from 0 to 1.0 for NA, 0 to 4 for forced-induction)

Good definition for both here: http://obdcon.sourceforge.net/2010/06/a ... ad-value/
mituc
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Re: No "calculated load" even though its a standard PID?

Post by mituc »

beernose wrote: July 7th, 2021, 5:27 pm While logging today, I noticed that I have 'Absolute Load" as defined by OBD2 spec, but the Calculated Load is not available in the "All parameters" list.

I noticed it mentioned as available for other Mazda variants of VersaTune. Is this just an oversight in the RX8 version?
It's the same for all other platforms as well, but the thing is that on any platform (mazda or another) the absolute load is not taken into consideration anywhere in the tunes, factory or otherwise, because it's pretty much useless in any regard in a forced induction engine (let's say that in a supercharged engine you could set a limit based on the volume of the supercharger and pulley size, but you'd have to change that again if you make any changes).
Modern ECU programming would rather adjust targets (AFR, timing, calculated load, and so on) based on barometric pressure and then have everything computed properly based on the volumetric efficiency tables + various corrections based on the readings from the engine sensors (MAF, MAP, BARO, O2).
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071, ~476WHP @31-32PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 320-ish BHP
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