As Mitchell stated I also have the minicats end of preoblem as above
On cars which have high flow cats, what exactly is the minicat doing? I understand it uses real cat material, but is it a proper measurement of what is going on in the main cat (with respect to exhaust gases)? Does the post cat signal going to the ECU affect tuning (fuel/air ratio, etc)?
According to the WSM, yes. Image Unavailable, Please Login The way I interpret that is that it effect LT fuel trim.
I believe that the changes would be that minimal to fuel trim it would nearly be insignificant from what original tune parameters are set. If the changes needed were high to match front and rear cat readings or specs that alone would cause a CEL. In saying that from what I have read the post cat 02 sensor is sensitive.
From my memory, the rear O2 sensor main function is to decide if the cat converter is still efficient. In the event where the front O2 sensors are defective, the rear O2 sensor will contribute to the ECU management of the engine. To what extent? I do not know.
I found this write up on the Bosch system. Not sure if it applies to the 5.2, but seems pretty logical. Seems it corrects for switch point drift by changing the additive value. That sound like LT fuel trim to me. An ageing sensor's switch point will drift to a different voltage.
Thanks, gents. I underestimated the detail available in the WSM, but, as stated, the degree of control is not really known. I can't tell if the minicats (with real cat material) are any better than the steel wool type at determining the condition of main cat material because minicats can be successfully fitted to gutted cats. There is a disturbing claim in one eBay advertisement for a minicat made in China... "And our CEL eliminator is one kind of small catalytic converter in front of the O2 sensor, so if your real catalytic converter is broken, the CEL eliminator can help you to reduce the toxic gas. " I don't think a penny-sized piece of cat material in an extender is going to noticeably reduce toxic gases in a tailpipe. (EDIT: just read John's last post. Very interesting. Thanks)
