The port on the connector pipe is for checking emissions level before
the cat with a co meter (sun and sum).  I don't know of a o2 sensor
that will fit this port.  Its should have a 3/8" cap on it I think.
Use Bulley's method to remove the  old O2 sensor.  Tap on the base
for a few minutes, hard with a 7/8" socket or box wrench.  That
should loosen it up.  It always has for me.

I have a test O2 sensor permanently installed on my 77 bay window.
It helps me  set up the fuel mixture  adjustments on the AFM.   If
you follow the procedures in Bentley or the Pro Manual.  An
additional unit should not be necessary.  I believe you can connect a
parallel meter connection on the present  O2 sensor without degrading
the signal.  Isn't that what the Digitool does?

Steve

>Hey guys, what about cold temperature!
>
>I tested mine today for fun!!! (2.1L) (about 40F) and i have no reading?
>450MV means nothing!!!
>
>Another good question, i have the OS on the cat but my new U pipe (the one
>between the cat and the Y connection) as a hole under for the OS??? (near
>the cat )(i think it's for the 1.9L also)
>
>For sure the original is stuck there and i was thinking of leaving the old
>one there and adding the new one to the U pipe just for fun and also to
>make some test. Yes the old one look like it's the original one. I banged
>it, i did heated, put some loose nut and it's still stuck there, for
>ever!!!(joke)
>
>What are you're taught about using the U pipe hole?
>
>Ben
>http://www3.sympatico.ca/huotx/engine1.htm

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