closed-loop target lambda

[phantom_]

hello,

i changed closed loop target lambda setting from 14.67 to 13.50 in order to experience the effect.

thru datalogs, ECU is still trying to reach ~14.7 AFR value where closed loop mode is active. is it possible that this feature is not implemented for the Euro S?

[Spunkster]

Calibration and datalogs showing this?

[phantom_]

let me generate datalogs with 14.67 & 13.5 and attach to the thread together with calibrations...

[phantom_]

attached are the calibrations and their datalogs (in the following message).

changing only target AFR value at each calibration, i created 3 calibrations for 14.67, 13.5 and 15.2 respectively. i did not change STFT range.

i did not use live tuning but uploaded calibration before each datalog in order to keep it simple.

i tried to drive the S in closed loop (i.e. no WOTs at all).

my evaluation: i did not observe any obvious drift to 13.5 or 15.2. however, AFR values fluctuate a lot, so in order to be objective; i used the histogram function of FPM. all of the 3 datalog AFR values accumulate on ~14.7 value.

Hondata, can you pls comment?

[phantom_]

datalogs...

[phantom_]

hello hondata support,

in the previous thread, i attached calibrations & datalogs for the possible FPM closed-loop target lambda bug, can you please check?

[Hondata]

For the ECU to change the target lambda from 14.7, all three tables and the overall target must be changed. Just changing the overall target will not have any effect.

[phantom_]

about the all three tables, do you mean the closed loop target lambda limit/low load/high load with respect to ECT tables below?

Screenshot.png

[Hondata]

Yes.

[phantom_]

hello hondata,
below is an excerpt from a Wells Vehicle Electronics newsletter;

When the oxygen sensor reports a rich mixture, the fuel system powertrain control module (PCM) responds by commanding a lean mixture. And when the oxygen sensor reports a lean mixture, the PCM responds by commanding a rich mixture. This is classic “closed loop” fuel control, with the PCM always a step behind in its response to the rich or lean voltage signal from the oxygen sensor.

This would seem to be an inefficient means of controlling the air-fuel ratio. Why not find an air-fuel mixture that is close to ideal (stoichiometry) and keep the mixture as near to that point as possible? Why must the fuel system constantly overshoot its goal as it moves from a too-rich to a too-lean air-fuel mixture and back again?

The answer can be found in the design of the catalytic converter. The threeway catalytic converter needs a rich exhaust mixture (low oxygen content) to reduce oxides of nitrogen (NOX) emissions. However, it also needs to receive a lean exhaust mixture (high oxygen content) to oxidize hydrocarbons (HC) and carbon monoxide (CO) into carbon dioxide (CO2) and water (H2O) vapor. If the exhaust stays rich, the catalytic converter can’t reduce CO and HC emissions. And if the exhaust stays lean, the catalytic converter can’t reduce NOX emissions. Alternating between rich and lean allows all three goals to be reached.

according to the above, STFT provides the required AFR oscillation. that is why we have an adjustable range for STFT in the below calibration window. can you please confirm this?

stft.jpg

now, my question; my S has a testpipe instead of the cat. is it logical to zero STFT range, since i do not need any catalytic operation engagement?
is LTFT directly related with STFT calculations? does zeroing STFT range disable LTFT calculations?
i preferred to ask you if the above AFR oscillation by STFT adjustment is valid for F20C ECU and if STFT disable harms the engine, stops LTFT or not, before executing any changes...

[Hondata]

The short answer is the closed loop oscillation is not necessary for the catalyst function and primarily is of the o2 sensor hysteresis, and so the oscillation is required to achieve a stoichiometric AFR. I would not make any changes to closed loop if not running a cat.