VersaTune User Forum

I'm trying to command leaner AFRs on my 3MPS BK (mazdaspeed3 gen1) but whatever I do it goes back to stoich. I hoped that commanding just slightly leaner (just for cleaner burns, nothing major) below 1.03 lambda (1.01-1.02) will trick the ECU into accepting it, but it actually doesn't.
I instructed a few friends to disconnect the secondary O2 and I successfully tuned their cars with leaner AFRs in closed loop which improved closed loop fuel economy quite a lot and resulted in cleaner burns. But this doesn't work with the cars that have the secondary O2 still plugged in.

Are there any tables that need to be exposed or it there any of the existing tables that can be tweaked to achieve this without disconnecting the secondary O2?
I guess another approach would be to disable fuel trims above a certain load point set very low (0.25) and trick the ECU using the MAF calibration, but closed loop fuel trims are really helpful so I would not go this route.

Hmm... Actually I can force the ECU into open loop without giving up on fuel trims!

...But EGR will not be activated during cruising if the ECU is in OL... Hmm... tough choices...

I noticed that the CX7 firmware is a bit more relaxed when it comes to (slightly) leaner AFRs. It at least commands 14.71-14.76 in those areas where I command 14.85-15.1 (1.01-1.027 lambda).

At least around here the emissions test which we have to do every 2 years for cars newer than 10 years and then yearly for cars older than 10 states that the lambda should not exceed 1.03, which is the reason why I stopped at 1.02 but those extra 0.02 would give the cats some oxygen to work with and burn even cleaner the remaining soot.
Also, because the 3MPS gen1 and CX7 gen1 (and all 6MPS/Mazdaspeed6) meet the EURO4 emissions standard going too lean may affect the cats in time. It is possible that the gen2 Mazdaspeed3 (3MPS BL) and gen2 CX7s have have slightly different cats since they are EURO5 which I doubt, basically only the EURO6 cats support leaner AFRs of 16-21 (on de-catted setups with secondary O2 disconnected I stopped at 16.5 to avoid the low load/rpm throttle response hysteria).

Steve, Ugnius, any comments? Or can this lead to a feature request?
I attached the closed loop commanded AFRs on my CX7, they loop kind of similar on my 3MPS.