Service Repair Manual

GENERAL (FBC)
2. Sub-vacuum Timing Control
2) When the engine speed increases to 1,200 rpm the ECU
turns off the distributor advance control solenoid valve.
Intake manifold vacuum is routed to the main vacuum
chamber increasing ignition advance.
When the engine starts to warm up [engine coolant
temperatures: below 80°C (176°F), the solenoids are
energized,
allowing D port vacuum to reach main
vacuum chamber.
o Control at low altitude [approx. 1,200 m (3,900 ft.) or
lower]
1) When the engine coolant temperature is low [50°C
(122°F) or lower], the ECU energizes the distributor cold
advance control solenoid valve. By this action, the intake
manifold vacuum no longer leaks to atmosphere and
instead is introduced to the sub-vacuum chamber. As a
result, the timing advanced by the main vacuum advance
is additionally advanced by a fixed angle (5°C in crank
angle).
2) During warm-up operation or when the engine coolant
temperature is- high [over 50°C (122°F)], the ECU
de-energizes the distributor cold advance control
solenoid valve circuit. As a result, the intake manifold
vacuum leaks to atmosphere, which prevents timing
advance.
o Control at high altitude [approx, 1,200 m (3,900 ft.) or over)
At high altitude, the HAC is closed and hence the intake
manifold vacuum does not leak to atmosphere from the HAC.
Independently of the distributor cold advance control solenoid
valve, the intake manifold vacuum acts on the sub-vacuum
chamber, causing the timing to advance by a fixed angle (5°
in crank angle). [For Federal]
31-86