EMISSION
AND
EVAPORATIVE LOSS CONTROL SYSTEMS
16
Fig.
1S1
OJlY9'lO Sensor
The Oxygen sensorls) require replacement at the intervals
stated
in
the maintenance summary, and a reminder lamp
on the fascia
will
illuminate at this mileage interval. Please
see your
Dealer,
or
qualified service outlet, as soon
as
convenient
after
the reminder lamp illuminates.
Overrun
Valve
This second air flow control device bleeds air into the engine
inlet
manifold, via the piunum chamber, when the manifold
depression
is
hIgh and thus maintains combustlOn dUring
engine overrun.
The valve operates independantty of the electronIC control
system and on TAJ models
IS
mcorporated
In
the throttle
butterfly
connectmg the constant depresslOn region between
the throttle and the Air Flow
Meter
measuring flap
On
ve
models It
IS
a separate valve on the sIde of the thrOllle body
Oxygen Sensor
A smgle sensor
IS
fitted to TAJ models and
two
sensors are
fitted to TAe and
Rover
3500
vehicles They are located
In
the exhaust system near to the catalyst(s) and. like the
catalyst(sl. reqUire only
UNLEADED
fuello
be
used to prevent
damage to them. These sensors monitor the composition of
exhaust gases leaving the engine
The Internal workmg surfaces of the sensors are coated
wllh
a thin platinum layer which
IS
permeable
to
gas A speCial
ceramiC layer protects the electrodes agamst corrOSion and
thiS become conductIVe to
olCyQen
atoms at about
600°C
11112°F)
If the concentration of oxygen mSlde the sensor
(from the exhaust gasesl differs from that outside the sensor
(atmosphere) a voltage
IS
developed between the two
surfaces that changes when the outer electrode has catalytiC
activIty
ThiS
voltage
IS
passed to the EC U
which
compares
It against a reference voltage for Ideal combustion and
adjusts the main injector 'open'
lime
accordingly to permit
more or less fuel to be used by the engme
More
fuel will use
up the excess oxygen
m the exhaust gas. less fuel Will allow
more oxygen, and so the ideal oxygen content
IS
supplied to
permit the catalyst to operate at
ItS
best effiCiency
Conunued
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