Hyundai Sonata 1991 Shop Manual page 246

MPI SYSTEM
Calculation Of Ignition Timing
1. The period (T) of the crankshaft angle sensor signal is mea-
sured, and from this the time (t) required for a rotation of
1° of the crankshaft is determined.
t=T~180
2. The ignition timing (T1) is caluculated, with 75° BTDC as the
reference standard, and the ignition signals are sent to the
power transistor.
Example (at ignition at 20° BTDC):
T1 = t x (75-20) sec
(a) Control During Ignition Timing Adjustment
When the ignition timing adjustment terminal is grounded,
there is synchronization with the crankshaft angle sensor's
signal, thus resulting in the fixed ignition timing (5° BTDC),
and in this condition the reference ignition timing is
adjusted.
Note, however, that the spark advance becomes the same
as control during ordinary driving if the engine rpm becomes
the set rpm (1200 rpm) or higher.
(b) Control During A Malfunction Of The Air-flow Sensor
If a malfunction of the air-flow sensor occurs, there is control
to the greatest load of the map value set to each engine
revolution and intake air amount. This is equivalent to the
centrifugal spark-advance characteristic of a conventional
distributor.
T (Crankshaft angle 180°)
BTD~BTDC
75° 5°
I
Crank
:~~~:r~,
b
Ignition _ _
-I
pulse ' - - - - -
Time count stan
31YQ11
31-21