Saab 1987 900 Owner's Manual page 47

exhaust manifold monitors the oxygen con-
tent ofthe exhaust and sends a proportional
signal to an electronic control unit (under
the rear seat). This signal is compared to a
predeterminded value and an output signal
is sent to a fuel pressure modulating valve
to make the necessary fine adjustment of
the air/fuel ratio. Until the sensor warms up
after the engine is started, the modulating
valve will operate at a constant predetermi-
ned value and in the event of sensor failure.
A maintenance reminder lamp, labeled
"EXH", on the instrument panel illumina-
tes every 30,000 miles to indicate that the
oxygen sensor is scheduled for replacement.
(After this service is performed your dealer
will reset the lamp actuating mechanism).
Note: 16 valve engines also have an oxygen
sensor but it is a different type which is to
be replaced at 60,000 miles. These models
do not have the reminder lamp.
F. Three-way catalyst
The catalytic converter contains a special
platinum and rhodium coated dual seg-
ment substrate which simultaneously frees
oxygen from oxides of nitrogen and oxidizes
(burns) hydrocarbons and carbon monox-
ide. Unleaded fuel is required to protect the
conversion efficiency of the catalyst.
S 5751
Catalytic converter
1. Ceramic insert
2. Channels
3. Catalytic coating
II. Crankcase emission
control system
A completely closed crankcase ventilation
system is used. Crankcase fumes are drawn
directly into the inlet manifold under all
operating conditions except full load and
high blow-by when some gases are diverted
ahead ofthe throttle body. The oil seperator
in the valve cover also serves as a flame arre-
stor.
Technical description 45
4 5 8 6
1 Crankcase
2 Exhaust manifold
3 Camshaft cover
4 Oil trap and flame
arrestor
9 7
5 Nipple with orifice
6 Hose
7 Inlet manifold
8 Check valve
9 Hose to inlet pipe