During my scanning logs to get VE dialed in Ive been focused on the WBO2 graphs but recently noticed my narrow band o2s are almost flat lined reading rich almost all the time. do the narrowband o2s still switch when in SD mode ? Tried another set of O2s with the same results when they are unplugged they read 451mv.
They would be switching if you didn't have closed loop fueling disabled. A wideband and narrowbands are never going to agree...there will always be an offset between the lambda that results from the NB O2 derived fuel trims and the lambda the WB reports. They're just different styles of sensors. WB is linear, NB is not.Originally Posted by metalmanimal
If the WB is working properly, the point at which the NBs switch should occur at a consistent reading of the WB.
right, the 14.7:1 on both sensors should be more or less identical, I often use the narrowband 14.7 as a way to tell whether the wideband is working or not.
but remember to take into account any exhaust leaks, and any excess cooling of either sensor, and also remember some narrowbands have actual ground connections (wires) and some simply ground through the exhaust system metal, which can also affect reading (i.e. 1-wire narrowbands)
I thought they always switched, no matter if in SD or OL. I'll turn them back on and see how they behave.
Thanks
they only switch in CL when the ecu is in the routine of keeping fuel at the stoich point, when in OL they will just be following what afr they see as if they were a rear 02 sensor, it only takes like 0.3 or so afr change to move the narrow bands full range as they are just a stoich tuning tool
What would make it go over/under 450mv if it's in open loop? It's not adjusting based on feedback in that situation. In closed loop it's constantly hunting for stoich because it's using feedback from the narrowbands to tell it to add or subtract. In open loop it's just doing what you put in the tables.
Switching is due to proportional fueling control in the ECM. It is actually a driven oscillation that exists to periodically deliver oxygen into the catalyst so that it can catalyze emissions products of both lean and rich combustion. Without that constant plus and minus fuel offset during closed loop, the sensors simply read the open loop output of the fueling control. If you were super accurate with your open loop fuel, as in dead on at stoich, the narrowbands will still appear to switch very rapidly because the voltage slope from the sensor near stoich is almost infinite. It's called switching because that's the intent; switch from a lean reading to a rich reading very quickly and allow the ECM to maintain a calibrated quantity of stored oxygen in the catalyst.
I used to do this as a day job, so I could talk about it for a while lol.
Smokeshow, or anyone else, what would you suggest in the case with no cats, but still wanting to use closed loop? Obviously you would no longer need to have a stored quantity of oxygen, you just want it to run at stoich as close as possible. I am guessing that one could severely tighten the rich/lean switch point mV, and probably dial back the proportional, and/or the limit?
I am still not entirely sure how the R/L settings come into play. My stock cal has the R/L vs airflow numbers increasing with higher airflow modes, from a low of 61 mv to a high of 328 mv (both banks the same), then the cold offset adder, yet the Min and Max settings are both at 450 mv. So at what mV it is really going by for switching, I am not sure.
Realized that this is the Gen3 forum and I am referring to a Gen4, but the same principles should apply though with slightly different levers to pull. Here are my stock settings for r/l and offset voltages.
O2 volt offsets - stock.JPG
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