CJ-7 L4-150 2.5L VIN U 1-bbl (1983)
Powertrain Control Module: Description and Operation
Modes of Operation
1983-86 4-150
This CEC fuel feedback system has four modes of operation: Key-On, Start-Up, Warm-Up and Cruise.
Key-On Mode
In this mode of operation, the MCU, bowl vent solenoid and the Sole-Vac holding solenoid are energized when the ignition switch is turned to the
``On'' position. Also, battery voltage is applied to the idle relay, and the PCV shut-off valve is energized by the MCU through the anti-diesel relay.
Start-Up Mode
In this mode of operation, the ignition switch is in the ``Start'' position and the starter motor is energized. Alternator voltage output energizes the choke
relay. If engine coolant is cold, the intake manifold heater switch closes to activate the heater. A ``Start'' signal and engine RPM voltage from the
distributor is sent to the MCU, which then controls ignition timing.
Warm-Up Mode
In this mode of operation, the system is in ``Open Loop'' operation and the MCU receives input from its data senders. The 4 inches Hg vacuum switch
is in the ``Open'' position (vacuum less than 4 inches Hg) and the 10 inches Hg vacuum switch is in the ``Closed'' position (vacuum less than 10 inches
Hg). The coolant temperature switch closes at 135° F (57° C) and the closed throttle switch is closed. The thermal electric switch opens at 65° F (18° C),
then the manifold heater switch opens at 160° F (71° C). The MC solenoid is controlling a pre-programmed fuel/air mixture to the carburetor, and the
upstream and downstream solenoids distribute air to either the exhaust pipe or the catalytic converter. If accessories such as the rear window defogger or
the air conditioner are in operation, the Sole-Vac vacuum actuator is activated. The Sole-Vac vacuum actuator is also actuated during deceleration, or
when the steering wheel is turned to its full stop, on models with power steering. The MCU controlled shift indicator light circuit is opened when the
transmission selector lever is placed in 4th gear, on vehicles with manual transmissions.
Cruise Mode
In this mode of operation, the system is in ``Closed Loop'' operation and the MCU produces outputs. The CEC components are controlled as in the
warm-up mode and the MCU accepts input from the oxygen sensor. The MCU controls the MC solenoid and may receive input from the knock sensor to
advance or retard ignition timing. The upstream and downstream solenoids route air to the exhaust pipe or the catalytic converter. The WOT switch and
closed throttle switch indicate throttle position. The MCU controlled shift indicator light circuit is opened when the transmission selector lever is placed
in 4th gear, on vehicles with manual transmission.
