rear o2?

[Michael Jez]

---I would hold the engine at around 2500RPM and watch the voltage reading
change from rich to lean back and forth pretty fast, it it stays at once
spot or another for too long, U got a dud---
>From my 1st msg, the only O2 sensor that switches over quickly from lean to
rich is the upstream sensor- which is on the manifold or secondary pipe.
Thats the one I reffered to as a dud. Only way of checking cat efficiency
properly is using a 4 or 5 gas analyzer. Rear O2s do not switch that
quickly, and they stay pretty consistant at higher cat temeratures. It
should be a linear line on the osciloscope when the cat is at 1200 deg F- or
whenever the cat is at its peak thermal efficiency-depends on cat size and
where its located . The line will move up and down depending on the
temperature of the cat when watching the o-scope. Since we are talking about
a Nissan its safe to say O2 sensors are bad. When cars are not driven alot
and sit alot condensation in the exhaust kills the O2 sensors- why alot of
Maximas have O2 sensor problems. I seen cars with 15K miles on them and they
are 98s or 99s and need O2 sensors, mine has 50K miles its a year old and O2
sensors work just fine. If U remove the cat on a OBD2 car and there is a
downstream O2 sensor on the car U will get a check engine light. Now Honda
gets away with only 1 O2 sensor on some of their V6 cars and its before the
cat- and its certified as ULTRA LOW EMISSION vehicle... they are OBDII. They
also like to use 5 wire O2 sensors which are ultra sensitive and are a low
cost tuning tool if ya wanna fine tune your A/F mixture on a Apexi S-AFC.
Mike Jez
Honda Trans/Engine Certified Tech
Audi Trans/engine Certified Tech.
> I didn't deny that it was for monitoring the cat.  You were not
> clear when you said "U got a DUD." I assume you were referring to
> the CAT being bad and not the O2.  The rear O2 when the cat is
> good switches longer from rich/lean then the front O2.