Subaru 2002 Impreza Service Manual page 83

CONTROL SYSTEM
Fuel Injection (Fuel System)
Crankshaft position sensor
+
Camshaft position sensor
b
D: IGNITION SYSTEM CONTROL
Mass air flow and intake air temperature sensor
0
The ECM determines operating condition of the engine based on signals from the pressure sen-
sor, engine coolant temperature sensor, intake air temperature sensor, crankshaft position sensor
and other sources. It then selects the ignition timing most appropriate for the condition thus deter-
mined from those stored in its memory and outputs at that timing a primary current OFF signal to
the ignitor to initiate ignition.
0
This control uses a quick-to-response learning feature by which the data stored in the ECM
memory is processed in comparison with information from various sensors and switches.
0
Thus, the ECM can always perform optimum ignition timing taking into account the output, fuel
consumption, exhaust gas, and other factors for every engine operating condition.
0
Ignition control during start-up
Engine speed fluctuates during start of the engine, so the ECM cannot control the ignition timing.
During that period, the ignition timing is fixed at IO" BTDC by using the IO" signal from the crank-
shaft position sensor.
+
ECM
Ignition coil
and ignitor
assembly
plug #2
-4
plug Spark #3
I
-
NF0432
FU-33