Saab 900 1983 - Page 29

B. Decel Dashpot (Automatic
Transmission
Only)
The decel dash pot acts upon the throttle
linkage to minimize incomplete c omb ustion
during engine deceleration.
C. Decel Fuel Shutoff (Manual
Transmission Only)
A solenoid operated air by-pass valve reduces
air
flow in the air flow sensor, lowering the fuel
distributor plunger interrupting fuel flow during
dec eleration. The solenoid is controlled by an
engine speed relay and a throttle contact
switch. During deceleration at engine speeds
above
1575 RPM the solenoid opens the by-pass
valve. When the speed
drops below 1375 RPM
the system de-activates allowing normal opera·
tion.
D. Lambda Control System
Lambda Control System is a closed loop feed-
back system adapted to the C.1. System to con-
stantly maintain close airlfuel ratio co ntrol
under all operating conditions. At an airlfuel
ratio of 14.5 to one (Lambda = 1 at this ratio), all
three
regulated pollutants (hydrocarbons, car-
bon monoxides, oxides of nitrogen) may be si-
multaneously controlled efficiently by a special
threeway
catalyst. An oxygen sensor in the ex-
haust manifold monitors the oxygen content of
the exhaust and sends a proportional signal to
an electronic control unit ( under the rear seat.)
This
signal is compared to a predetermined
value and an output signal is sent to a fuel pres-
sure modulating valve to make the necessary
fine adjustment of the airlfuel ratio . Until the
sensor warms up after the engine is started, the
modulating valve will operate at a constant pre-
determined value. This is also true in the case of
wide open throttle operation or speeds above
3800 RPM (Turbo only) and in the event of sensor
failure (the car will not be disabled)
A maintenance remi nder lamp , labeled " EXH ",
on the Instrument pane l i lluminates every
30,000 miles to ind i cate that the oxygen sensor
is scheduled for replac ement ( After this service
is
performed your dealer will reset the lamp ac
tuating mechan ism.)
3
1. Electronic Control Un it
2 Wide
Open Throttle Switch (Turbo only)
3. Oxygen Sensor
E. Three·Way Catalyst
The catalytic converter contains a special
platinum and rhodium coated dual segment
substrate which simultaneously frees oxygen
from oxides of nitrogen and oxidizes (burns)
hydrocarbons and carbon monoxide . Unleaded
fuel 15 required
to protect the conversion effi-
ciency of the catalyst.
4
4 C atalytic Converter
5. Mo dulating Valve.
5
27