Closed loop swing

[Mick]

Most of us are aware that the closed loop fueling will oscillate/cycle around stoic to keep the cat lit up, but is anyone aware of where this actually is in the tune? Or a scaler that controls how far it can swing?

[Roland@pcmtec]

I will try to dig this up for you when I'm on the PC.

[Mick]

Thank you very much, I’ve had a bit of a look but have yet found it

[Roland@pcmtec]

The upper and lower switching limits are defined by crossing the value found in the following scalar (eg the midpoint)

auF1240    Upstream EGO switchpoint    0.45v

It then adds and subtracts the following value to the switch point to calculate the upper and lower swing points as the initial setpoints (so it will swing rich/lean very quickly)
auF10314    Rich or lean increment to the rich or lean vego average.    0.1 v

These upper and lower values are then changed dynamically and can be datalogged via the following DMRs

MID125531 The rich average of vego voltage

MID125498 The lean average of vego voltages

There is a lot of crazy logic behind this where they age the O2 sensor and catalyst and constantly adjust these values to try and get the same switching frequency. There are some good public patents you can search on google to read about this in depth.

The actual amount of time it holds the rich/lean toggle I believe can be modified via the following scalars, though you'd need to experiment to be sure.

auF2267 proportional gain (I think this will be the main one)

Then the following all look interesting to play with.

auF2242, auF2124, auF1391, auF1255

Ultimately the switching speed is already optimised for maximum catalyst efficiency, eg the faster the better (within reason). If its not switching fast enough it will be due excessive transport delays, catalyst failure or o2 sensor failure etc.