Auxiliary Air Valve; Ignition System - Subaru XT 1988 Service Manual

2-7
FUEL INJECTION SYSTEM
Auxiliary Air Valve
(1800
cc
model only)
The auxiliary air valve is used to increase air flow when the
engine is started up at a low temperature and the following
warmup is performed. It consists of the coiled bimetal, the
bimetal-operated shutter valve, and the electric heater ele-
ment for bimetal. The passing air flow (at start-up) is increased
as the temperature becomes lower. After start-up of the
engine, the heating is performed by the heater to which
current is supplied from the fuel pump relay circuit. Thereby,
the shutter valve turns gradually to decrease the air flow. After
a certain elapsed time, the shutter valve is closed.
AIR IN
.....
Valve fulcrum
Fig.
6
Rotary valve
-.... AIR OUT
L2-1089
6
Ignition System
The ignition system is composed of a battery, an ignition coil,
a distributor, spark plugs, knock sensor, MPF I control unit
and wires.
The crank angle sensor built-in distributor detects the refer-
ence crank angle and the positioned crank angle. Electronic
signal of both angles is transmitted to MPF I control unit which
is used in common by fuel injection system.
The MPFI control unit calculates the spark advance angle and
determines the spark timing.
The electronic signal of spark timing determined by control
unit is transmitted to the power transistor where it makes
the primary circuit to ignition coil, whereby high voltage
current is generated in the secondary circuit.
The high voltage of secondary circuit is distributed to the
spark plug of each cylinder and discharged there.
UNDER NORMAL OPERATING CONDITIONS
The spark advance angle is calculated from the following three
factors.
1) Engine speed compensation.
2) Advance when starting the engine.
3) Advance in all driving conditions except starting the
engine, after engine speed exceeds the present value.
WHEN KNOCKING OCCURS
(2700
cc
model only)
A signal is transmitted from the knock sensor to the MPF I
control unit. The MPFI control unit then retards spark timing
to prevent engine knocking.
Knocking is
eliminated.
Advance
gradually.