I'm posting this image linked at very bottom link after watching ScannerDanner's vid on using pre and post O2 sensor response comparison, and response delay of rearO2 as a way of checking Cat Converter function. It's a great vid - https://www.youtube.com/watch?v=vyVnhCIMDnw
The twist here is that I'm using a system that has a AFR Wideband Front O2 and Narrowband rear O2 (or mid cat.
Car is Mazda6 2007 Gen1 2.3lt L3 Engine non-turbo, Auto.
I’m experimenting with wideband AFRs. Damn hard. Adds a layer of complication.
Car runs perfectly; but has a slight but persistent neg LTFT – around -5 to -8%. Never zero, never pos.
Yellow trace is a 5-wire AFR signal wire voltage trace (this has micro current changes to maintain stoich .. it also shows small V fluctuations: V reduces for Rich, Increase for Lean – opposite to narrowband O2)
The Pink trace is Post cat narrowband – it’s actually mid-cat on this car.
You’ll see that when I create a lean condition by pulling a vac hose the AFR does not change: maintains max lean state.
But mid-cat sensor reacts, going lean (normal low V)
When I add hydrocarbon spray via vac hose and pinch off vac leak, you see the AFR go rich (V drop), as does mid-cat (V rise).
Couple of points of interest:
1. AFR wideband behaviour is odd .. no lean response but immediate rich --- (scan data does however show lean/rich uA response)
2. There is a time delay, as you expect, between pre-cat and post-cat recovery from rich to lean/normal condition. But the delay is only 1.4sec … versus ScannerDanner expected delays of 4 seconds+ ... I don’t conclude that short delay is a Cat issue. Rather, I think it is a result of post-cat O2 actually being positioned mid-cat … ie shorter delay time? .
Can anyone explain the AFR behaviour lean response behaviour?
What do you think of response time delay of rear O2?
All comments/thoughts welcome:-) See this link for image (hope link works): https://www.scribd.com/doc/316302622/Waveform-O2-AFR-Narrowband-re-Post-Delay