Mike M > wrote in
:

> My son's 89 6 cyl.Cherokee just barely failed the Ca. smog test. It
> passed the 15 MPH but failed at 25 MPH on the "NO(PPM)" part of the test
> (max allowed is 875 PPM.his read 1066 PPM). Anyone have any ideas what
> the problem might be?
> The mechanic told him it is probably either the O2 sensor or the
> catalytic converter.
> TIA

Same thing happened to me. My '88 YJ failed miserably, though. I tried
everything I could think of to get it to pass. Finally I took it in to the
shop. The mechinic had me start it. First thing he came up with is the cat
converter was bad (granted it did sound like a baby rattle). After
replacing the converter and O2 sensor, I passed with reading down around
where they were when my Jeep was new.

Dave