As I said before, closed loop doesn't result in optimum performance, only optimum emissions. Optimum performance is typically found when running richer then stoich.

 

Ok what I meant was tuning for a specific afr (say 14:1 or 13.5:1) and have a closed loop system continuously adjusting for that specific afr. Of course this would be at wot, we'd have to use different settings for partial throttle, rpm, decceleration, etc. Is having real time adjustment any better or worse than just tuning with a static map?

 

You would think that would be the direction things are going. The ECU computing power is more powerful than what they used to go to the moon...so it should possible. The problem is that Mazdas idea of tuning has much more to do with emissions than any thing else after a certain point. It would be nice if we could harness the power of the ECU, and maximize power.....to hell with emissions!


I Know.....just dreamin' :D

 

Your dream has come true..... Go with Motech or Haltec

 

Sure...and loose ,DSC, Drive by wire throttle and a lot of other functionality of the intake etc

No thanks.....until there is an all incompassing, standalone or reprogram...I'll stick with my E-manage

 

Cool Sorry I didn't get your meaning first time. It would be interesting for the PCM to tune to a different ratio than stoich. In theory to me it shouldn't be much different to tuning for stoich - it would be looking for a different target AFR. Hey it would be interesting to try it and see what it did to fuel economy :p

 

On a production car, you need a close loop lambda control as an open loop control (based on static maps as you say) would be unable to adjust the AFR on stoichiometric within the required tolerance (+/- 3%) for optimum catalyst conversion efficiency. This inaccuracy in open loop mode is due to the stack of tolerances in all the sensors (MAFS, ECT,...) and actuators (injectors).
In fact, the PCM does not keep AFR exactly stoich (lambda 1) but gently cycles (can't remember the frequency though) around that value (but within the 3% catalyst conversion range) to optimise in turn HC and CO oxydation and NOx reduction.

I don't know why Mazda is not using the wide band functionnality of the system to run in close loop even in WOT conditions. This puzzles me but it might be a conservative decision. I will ask some ex-colleagues at Ford and Denso to see what they think. Note also that most of the high load and high speed AFR is governed by the catalyst temperature protection strategy. This traditionnally is an open loop and inferred (no actual measurement of cat temp) strategy.

Regarding what SCO is saying above, it would be nice indeed to improve fuel economy by running at best BSFC AFR. As the lambda sensor is of the wide band type, it could maybe even be done while maintaining close loop operation. However, this would be perfectly illegal and easily measured by a standard emission test. But I'm thinking about a way around it (a perfectly legal way).

Hope it helps (or confuses you even more???)

Fabrice