way more, the change rate may be too slow, the heater could be faulty,it could be a goodreading with a leak, but all in all if your gonna get a y pipe, who cares, its gonna throw codes then anyways so you need to get an o2 simulator. tom is right thatchanging the o2 isnt a bad idea, however i am not the type of person to change parts and hope that works, i would rather diagnose it right the first time and know it was the right fix. you can add propane through the intake and watch the switch rate of the primary o2 sensors. then you should see a rich mixture with a lean command when the secondary confirms that you are running rich because of the propane. if the secondary goes way rich then the cat isnt working and there is the problem, but in the state of california law requires that for a tech to diagnose a cat failure it must fail 2 out of three tests first then they can recommend a new cat. hope that helps
YOU DONT DRIVE A PIECE OF JUNK SO DONT FIX IT LIKE ONE.
IF YOUR NOT GONNA DO THE JOB RIGHT THE FIRST TIME, YOU SHOULDNT BE DOING IT AT ALL