I have a 99 GT with stock California exhaust, it came from the factory with 3 CATs on each side. I've never had any issues getting it to pass SMOG here in California, until this year. It just won't complete the drive cycle test for the CAT & EVAP. It hasn't completed the EVAP in years and here in CA it'll pass with one test incomplete. But now I have two incomplete. I've been using the Ford ODBII drive cycle guide and trying to drive the car in a manner to complete the CAT test. I've been doing it several times a week for a month, over 600 miles of driving. Still won't complete. I have noticed on my scanner while driving that my O2 sensors for B1S1 & B2S1 keep switching from "on" to "off" and back again consistently while driving. The other 2 sensors are always "on". Is this normal or does it mean my sensors or circuit is cutting out?