Duncan_GT

No i know what theyre for. Mjr said theyre not monitored on our cars, so then what is the point in having them if the computer isnt going to use them?

dawson1112

Mjr said the cats are not monitored . The obdI o2 sensors still monitor the exhaust to make adjustments in air/fuel , but on obdII there are 2 sets , a set that monitors upstream of the cats and a set that monitors downstream . The difference in readings between the upstream and downstream o2's gives the computer a look at how efficiant the cats are working.

mjr46

they are what send the ecu an input as to the content of oxygen in the exhaust stream, the more oxygen in the exhaust, the leaner the a/f is, the less oxygen, the richer it is, thus the ecu knows whether or not to lengthen or shorten the inj pulse width to get the a/f to the stochiometric perfect a/f of 14.7 to 1.

mjr46

I meant that obd 1 vs obd2 there are differences, a previous poster said mil eliminators could be used to turn off CEL......the CEL comes on when installing h-pipes on obd 2 cars cause the cats are no longer there and the rear o2's pick it up thus illuminating the CEL, 94 only has pre cat 02's and thus does not monitior cats, the precat o2's however, serve the same function on an obd 1 as they do for ob2

Duncan_GT

OHHH. They dont monitor the cats. My bad, i completely read your post wrong. I thought you were talking about the o2's, not the cats