Anyone ever heard of this setting? Is it only an ODB2 thing? It supposedly sets the voltage for what 14.7 afr is. Can it be used to swap a stock O2 sensor for a wideband O2 sensor to make it more accurate?

Hal

 

It actually (supposedly) sets the stoichiometric point, at whatever AFR ratio you want. 14.7:1 will always give ~450mv, since that's what the o2 sensors are designed to do. I have not heard of any success with this though.

Wideband o2 sensors operate completely different than narrowband ones. They give a 0-5 volt linear voltage/AFR reading, and use an 'oxygen pump' to generate a baseline. It's weird stuff, google it.

 

Its obd1 also. It does work but you need a wideband to play with it and figure out how much change you're getting. There is a related table in tunercat don't remember the exact name something about cl mode vs airflow. Basically it tells you which of the switch points to use based on the maf sensors reported airflow. Sometimes I use it to fatten the idle up a bit or work some surging out at low speeds by just adding a bit more fuel in a certain area. The table doesn't really have enough resolution to do anything drastic with it.

The ls1 guys play with it quite a bit, but if I recall correctly they have a table thats got enough resolution to be useful.

 

In Tunercat OBD I this threshold is called: "Fast O2 rich/lean threshold (mv) Vs. CL mode". CL Mode references the mass air flow and when the computer looks to transition as WS6T3RROR referenced and I agree it has minimal resolution for things such as surge. For some reason it is set at the factory at 407 for idle and 425 and cruise and above not 450...for a stock 95 tune.

When I recalibrate my MAF later this week, I intend to set mine to 450.

 

95Blackhawk:
"When I recalibrate my MAF later this week, I intend to set mine to 450."
This is interesting. 95Blackhawk, please keep us posted on what effects you see (or not) when you make this change. It would be nice (since it might be a few months down the road) if you bring this thread back to life or title a new one "Tunercat O2 Rich/Lean"
Thanks and good luck!

 

So you guys have got this to work and seen a different closed loop AFR?

You could lean out your freeway cruising AFR 10% and get 10% better mileage.

 

I read on one tuner's page that playing with the rich/lean threshold can be a way to improve mileage. I was actually thinking of trying it out, myself, to see if it made a difference.

 

Mine runs about 15.5-16:1 down the highway without much issue (minor bucking at 45mph with the stall locked). I also fattened it up in the lower airflow ranges to help get rid of a bit of surging. I have verified it on my wideband, it does work but it takes a couple of tries due to the numerous differences from car to car.

The thing is when you get to a point where it will make a difference even a small change will be HUGE.

 

What was your switch setting at to achieve this?

Granted, like you said there will be differences in cars but at least it is a starting point.

 

Generally to get it to work anywhere between 350 and 420mV is what I end up using. Again though this type of work is very much cut and check. I had one car with bosch sensors that went to that at 435mV... go figure.

Something else you will want to do is enable pe at lower throttle openings when you do that though. Otherwise you might cause lean misses under heavy load that isn't quite up to the tps pe threshold.