Saab 9000 - Page 22

Ignition system, knock control
The Saab Trionic ignition system is of capacitive
type. It consists of 4 ignition coils and electronic cir- .
cuitry
built into the ignition discharge module. The
ignition coils are controlled by the electronic circuitry
in the ignition discharge module, which is in turn reg-
ulated via low-level outputs from the ECM.
When the engine is cranked, the ignition system pro-
duces a spark on two spark plugs simultaneously,
1
and
4 or 2 and 3, for a number of consecutive com-
plete combustion processes. Following this, on the
basis of the ionization current flowing through the
spark plugs and signals from the crankshaft position
sensor, the system has sufficiently reliable informa-
tion for synchronizing spark generation and fuel in-
jection to the correct cylinder.
To improve starting performance when engine tem-
perature is below 0°c (32°F), the ignition system
generates a large number of sparks ("multispark"
function) when the starter motor turns the engine
over (10°BTDC- 20°ATDC).
The crankshaft position sensor consists of an induc-
tive sensor mounted in the crankcase wall of the en-
gine. The rotor is a perforated ring with 58 ribs
mounted on the rear counterweight of the crankshaft.
Technical Description 19
©
Ignition timing
Ignition timing is calculated by the control module
chiefly on the basis of the following information:
• engine load
• engine speed
• knocking, if any
• throttle position (idling only)
Saab 9000
I