Warm-Up Mode; Cruise Mode; Diagnostic Tests - Jeep 1987 Wrangler Workshop Manual

ENGINES
FUEL FEEDBACK SYSTEMS
• start signal provided to the MCU
• engine RPM (tach) voltage from the distributor
provided to the MCU
• MCU controls the ignition timing
Warm-Up Mode
In the warm-up mode, the system operates
as follows:
• system is
in
open loop
operation
i MCU receives certain inputs
• 4-inch Hg vacuum switch is open because the
vacuum is less than 4-inch Hg
• 10-inch Hg vacuum switch closed below 10-
inch Hg and open at 10-inch Hg vacuum level
and above
• coolant temperature switch closed at
57°C
(135°F)
• wide-open throttle switch open
• thermal electric switch opens at 18°C (65T)
• manifold heater switch opens at 71 °C (160°F)
(the manifold heater is off)
• mixture control (MC) solenoid or stepper
motor controlled by the MCU to provide a pre-
programmed amount of air for the air/fuel
mixture
• upstream and downstream solenoids con-
trolled by the MCU to distribute air to either the
exhaust or the catalytic converter
• Sole-Vac holding solenoid is activated if the air
conditioner is in operation (six-cylinder engine
only); also activated during deceleration
Cruise Mode
In the cruise mode, the system operates a s
follows:
• system is in closed loop operation
• MCU produces outputs
• components are controlled as in the warm-up
mode
• oxygen (0
2
) sensor input accepted by the
MCU
• MCU controls the mixture control (MC)
solenoid or stepper motor according to the
inputs
• MCU may receive input from the knock sensor
to advance or retard the ignition timing
• upstream and downstream solenoids route air
to the exhaust pipe or catalytic converter
• wide-open throttle switch indicates the throttle
position
Diagnostic Tests
Each C E C Fuel Feedback System incorporates
a diagnostic connector to provide a means for a
systematic evaluation of each component that
could cause an operational malfunction.
B-283