Hyundai Sonata 1991 Shop Manual page 245

Y31DF3A
MPI SYSTEM
Ignition Timing Control System
The ignition timing control system adjusts ignition timing by
controlling the power transistor which supplies current to the
ignition coil.
Air flow sensor (AFSI
Atmospheric pressure sensor
Intake air temperature sensor
Coolant temperature sensor
Power
transistor
Ignition coil
ECU
Throttle position sensor (TPS)
Idle switch
Vehicle speed sensor
Ignition switch-5T terminal
Inhibitor switch (A/T only)
Terminal for ignition
timing adjustment
AIT : Vehicle with an automatic transaxle
Crankshaft
angle sensor
Spark plug
~~~nition
iWitCh
~Battery
1
31'1'010
(a) Control During Starting
During engine starting, there is synchronization to the crank-
shaft angle sensor's signals, thus resulting in a fixed ignition
timing (5° BTDC).
(b) Control During Ordinary Driving
For each engine revolution and intake of air, and with the
preset map value as the reference ignition spark advance,
the coolant temperature correction value or the atmospheric
pressure correction value, whichever is greater relative to the
reference ignition spark advance, is applied as the correction
value, thus regulating to the optimum ignition spark advance.
o Coolant temperature correction
In order to improve driveability when the engine is cold,
the spark is advanced when the engine coolant temper-
ature is low.
o Atmospheric pressure correction
In order to maintain good driveability at high altitude, the
spark is advanced when the atmospheric pressure is low.
31-20