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OKAY - what the heck is going on with the CL/OP transition?!
I'm running Versatuner. Fuel trims are good, having good success tuning in the 6,000+ rpm region. My issue right now is in the 2,000-5,500 RPM range, basically in the region where the ECU needs to decide if it wants to be in closed loop (CL) or open loop (OL). My AFRs vary from pull to pull during the same drive, same tune. They're all over the place. it seems like sometimes the car is staying in CL much longer or shorter than other times.. basically, the transition from CL to OL as i go full throttle is wildly inconsistent. And it seems like the fueling is not very sensitive to the values in the air fuel table. I suspect that for unknown reasons sometimes the ECU is stuck in closed loop and using the acceleration enrichment tables instead transitioning to the open loop air fuel tables, even when calculated load and throttle position SHOULD be forcing open loop.
the transition from ~0.95 lambda to various much richer values seems to happen anywhere from 2,500 all the way up to around 5,000 rpms... kinda concerning to have been full throttle since 2,000 rpms and basically be seeing the car fueling near stoich at 5,000 rpms.
EDIT: I THINK I'VE LEARNED MY ANSWER.
Many S1s in the US have the load limit unknown table set to 1.0 (or close to it) until like 5,490 rpms, and this appears to prevent you from entering open loop under most conditions. As such, the car instead relies on the acceleration enrichment tables, which are just a little richer than stoic and only cover to 3,000 rpms. i assume this was an emissions and gas mileage tuning choice. i changed my load limit unknown values to around 0.65 - 0.75 as rpms increase between 2,000 and 5,490, and now it is easy to enter open loop and rely upon the air fuel ratio tables for tuning.
i attached a few data log snapshots. the first three are all the same tune, the fourth is a different tune but one where the car was super lean until 5,000 rpms.
Last edited by hufflepuff; Apr 21, 2026 at 05:17 AM.
Reason: knowledge!
If you must know when you're in CL or OL you'd best look at STFT. If it's 0 for a long time(2-3 secs) then you have entered OL 2-3 seconds ago. You can also log fuel system status to get a clear answer, OL/CL with fault/OL due to cold engine/CL and a few other cases.
As to why you get erratic AFRs thats just how open loop anything works: do things your way based on any number of inputs and hope for the best since you don't take any feedback. You don't (want to) know how well that turned out. For that I did a number on the ECU: https://www.rx8club.com/series-i-eng...ck-ecu-276077/
If you must know when you're in CL or OL you'd best look at STFT. If it's 0 for a long time(2-3 secs) then you have entered OL 2-3 seconds ago. You can also log fuel system status to get a clear answer, OL/CL with fault/OL due to cold engine/CL and a few other cases.
As to why you get erratic AFRs thats just how open loop anything works: do things your way based on any number of inputs and hope for the best since you don't take any feedback. You don't (want to) know how well that turned out. For that I did a number on the ECU: https://www.rx8club.com/series-i-eng...ck-ecu-276077/
Yes, thank you! The STFT going to zero steady and "fuel system status" dropping from 16 to 4 is a good sign you're in OL. I found out that load limit unknown was causing my headaches in forcing the engine into OL... i'll update my original post.
