Saab 1987 900 Owner's Manual page 49

' 1
charge pressure regulator (wastegate)
actuator. The
APe
system control unit has
been optimized with a fixed
~en.sitivity
and
pre-set high charge pressure hm~t to protect
the engine . Maximum operatmg charge
pressure under full load is electronically
governed. The wastegate is mechanically
adjusted to provide a safe, low charge pres-
sure limit should the
APe
system cease to
function.
NOTE! It is normal for "pinging" or
knocking to occur in short bursts whil.e
the engine is operated under load, partI-
cularly on lower octane grades of fuel.
When such knock is heard you may
observe the needle ofthe Turbo pressure
gauge oscillating sli$htly,
a~
ir:dication
that the APe system
IS
functIOnmg.
Intercooler
The 16 valve Turbocharged engine is fitted
with an inlet charge intercooler. The inter-
cooler is an air-to-air heat exchanger which
reduces the temperature of the engine inlet
air charge by the outside air which passes
across it when the vehicle is moving. Coo-
ling the inlet charge results in greater inlet
air density to allow for increased power
output and reduced thermal load in the
engine.
Ignition systems
The 900S is equipped with the EZK
bre~ker­
less ignition system which automatlcally
adjusts the timing to suit the grade offuel
being used. A control unit receives signals
from a knocking sensor on the engine block,
from a Hall sensor in the distributor and
from the fuel injection system. The control
unit compares the signals with those re-
ceived earlier and adjusts the ignition tim-
ing to suit.
Ignition control for the Turbo is provided by
a Hall sensor breakerless ignition with vac-
cum control.
Cruise control system
The electronically governed cruise control
system will keep the car at the selected cru-
ising speed without the need for the accele-
rator to be used. When the system is swit-
ched on, the vacuum pump starts to run.
This acts on the vacuum regulator which is
connected to the throttle control which
controls the position ofthe throttle to main-
tain the selected cruising speed. Informa-
tion about the actual speed ofthe car is sent
to an electronic control unit by the speed
transmitter. This control unit then compa-
res the selected speed with the actual speed
ofthe car. Ifthe speeds are different, a sig-
nal will be sent to the vacuum pump. The
vacuum pump will then act on the throttle
so that the correct cruising speed will be
Technical description 47
1
Switch
2 Speed transmitter
3 Vacuum regulator
4 Switches operated
by the brake and
clutch pedals
5 Electronic control
unit
6 Vacuum pump
resumed. A memory in the electronic cont-
rol unit enables the selected cruising speed
to be resumed after the brake or clutch
pedal has been used.