High Altitude Compensation (Hac) System - Toyota 4-Runner 1985 Repair Manual

EC-48 EMISSION CONTROL SYSTEMS (CARB.) - High Altitude Compensation (HAC) System
HIGH ALTITUDE COMPENSATION (HAC) SYSTEM
(Federal (Optior -,
Distributor
Primary Low Speed
Altitude Compensator
Port
Primary High Speed
Altitude Compensator
Port
Secondary High Speed
Altitude Compensator Port
Check Valve
Sub-diaphragm
Secondary High Speed
Altitude Compensator
Port
Check Valve
Distributor
Su bod iaph ragm
A03066
Primary High Speed
Altitude Compensator Port
EC0374
Bellows
Port A
Primary Low Speed
Altitude Compensator Port
Fuel Cut Port
EC0375
As altitude increases, the air-fuel mixture becomes richer. This system insures proper air-fuel mixture by supplying addi-
tional air to the primary low and high speed circuits and secondary high speed circuit of the carburetor, and advances
the ignition timing to improve driveability at high altitude (above 1,198 m (3,930 ft)).
Altitude
Bellows in Port A in Distributor
Port B in Air from Vacuum Ignition
HAC Valve
HAC Valve Sub-diaphragm HAC Valve HAC Valve Timing
Led into primary
HIGH
PULLED
low and high
ADV ANC ED
(+
1 ;
Above 1, 198m EXPANDED CLOSED
(Always)
OPEN speed circuits and
(3,930 ft) secondary high
(Always)
speed circuit
LOW NOT PULLED
INITIAL TIMING
Below 783m CONTRACTED OPEN
(PULLED OnlY)
CLOSED
STOPPED
(ADVANCED
(+
12°)
)
(2,570
tt) during idling
only during idling