Desired AFR Calculation?

Tuning discussion for all second generation Mazda RX-8 (2009-2011)
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dhancock14
Posts: 9
Joined: May 16th, 2018, 7:18 am

Desired AFR Calculation?

Post by dhancock14 »

I haven't really messed with Versatune much until now, but I've been researching a lot about tuning cars to prep for tuning my FD and decided to try to clean up my RX8 tune as practice. 11 AFR is way too rich for a NA rotary, so a long time ago I decided to lean it out a bit with no luck. Raising the minimum AFR's to 12 didn't seem to do much as the o2 sensor was still pegged to 11 AFR so I can only imagine how rich the stock tune values actually are. It wasn't until recently after my research that it hit me as to why it could be off target, so I started reducing VE table values above 6k rpm when open loop and found results. It seems like the MAF sensor settings might be off, at least for my car, because I had to take out around 8% VE to reach my AFR targets. I still need to find more information about tuning with a MAF sensor since most of the stuff I've researched is relevant to MAP sensors for my FD.

Well, this comes around to my question... because Versatune doesn't make it easy to view live sensor data and change AFR values at the same time on a single screen like aftermarket ECU manufacturers do. Isn't the Desired AFR value supposed to tell me my target AFR? It doesn't seem to know how to calculate desired AFR most of the time in the logs and the value is practically useless. It's particularly noticeable in open loop when my target AFR's at 7000 rpm and .9 load are set to 12 in the AFR tables, my actual AFR's are around 12, but "Desired AFR" is pegged at 14.5.

How is this value calculated? Why would it not even be close to the values set in my AFR tables? I would assume it's supposed to be a calculation based on AFR targets, IAT's, and probably other sensor readings, but it shouldn't be that far off my targets especially in open loop. It only seems to be somewhat accurate during closed loop, maybe 75% of the time.
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Ugnius @ VersaTune
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Posts: 580
Joined: March 19th, 2010, 11:57 am

Re: Desired AFR Calculation?

Post by Ugnius @ VersaTune »

Desired AFR parameter is most probably "closed loop desired AFR". There may not be an open loop desired AFR parameter.
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