Zeitronix zt-3 wideband calibration in link g4+ issue

[Copyninja]

Gentlemen, I feel like there is a 0.5afr discrepancy with my Zeitronix ZT3 wideband with the link g4+ ecu.

This is how its been setup/calibrated in the ecu. 

 

Now i've tuned my afr target table and everything was fine. However, as a test i changed the AFR target table from 13.5afr in the idle areas to 13.0 afrs and that immediately impacted and changed my real time afr readings reading 0.5afr richer without me making any changes to the main fuel table! This is obviously a bit concerning for me because whatever changes made in the target table should surely not change the afr readings? I'm not running closed loop or VE either. What am i missing here? Is my wideband faulty?

[Vaughan]

When Open Loop Lambda Table is on the AFR/Lambda target is taken into account in the fuel calculation and so changing the target will change the fuel volume and so measured AFR/Lambda proportionally. This means you can adjust targets without having to retune the fuel table.

[Copyninja]

Hi Thanks for the insight.

So say if ive tuned to a certain target lets say 11afr at 12psi. If i change the target table to make it richer......then its automatically adds in more fuel and vice versa less fuel? so effectively my afr is reading accurate? 

[Adamw]

I will give an example to hopefully make it a bit clearer.  

These examples are assuming open loop lambda table is enabled and the injector deadtimes are somewhere in the ball park:

Lets say at WOT your afr target table had 11:1 AFR in it, and you had tuned the fuel table so that when operating at WOT your measured AFR was actually close to 11:1.  

Then if you later wanted to try leaning it out a bit to say 11:5afr at WOT, then you only need to change the value in the target table, the fuel table remains unchanged.  The ECU will reduce the injector PW proportionally to the change in target and the measured lambda should follow the new target automatically. 

There are several advantages to using the open loop table - one is described above - you can change the target after tuning without having to retune.  Secondly, having the target factored in to the PW calculation makes your fuel table "flatter", there is less variation from cell to cell as load changes because the fuel table is effectively only compensating for a change in air flow rather than the change in fuel mixture target and airflow combined.  Thirdly, the target can be used as an "extra dimension" in tuning - for example with ITB turbo engines you may have TP as the load axis on the fuel table - but since at 100%TP you could have anything from say 0psi boost to 40psi boost you dont really want to target the same AFR for all boost pressures (you want to target richer as boost increases), so you can put MAP or MGP on the axis of the target table, then even if you are working in the 100% TP row of the fuel table the whole time, you can still vary the target based on boost pressure as well.  

[Copyninja]

Thank you that really makes sense now. Thats gonna add a layer of insane time saving on the dyno. I thought only ve based fuel tables could make that change. This is great information.

I think the issue i've got is the stock oem injectors for the rx7 dont have deadtime data from factory so i've left these as 0. 

However, the secondaries are asnu 1500cc so i've got all the data for that populated. 

I'm just happy that my afr readings are accurate and i can experiment more with the tune without changing the main fuel table. 

Thank you.

[Adamw]

Deadtimes that we have in our FD below (stock primaries), these would probably be better than having them set to zero.

  

[Copyninja]

Thank you so much, do you have the dead times for the oem secondary 850cc injectors by any chance? Im using the oem 850cc as my primaries. 

[Adamw]

I dont.  I would still use those values above though, they will be much closer than using 0.