Wrangler L4-150 2.5L VIN H TBI (1986)
Engine Control Module: Description and Operation
Micro Computer Unit (MCU)
MCU Inputs
Oxygen Sensor
The oxygen sensor provides a variable voltage signal for the MCU that varies with the oxygen content of the exhaust gas.
Thermal Electric Switch (TES)
This switch is mounted inside the air cleaner. When air temperature is below the calibrated value, the TES provides a ground circuit for the MCU to
indicate the necessity for a cold weather engine start. When air temperature is above the calibrated value, the TES provides an open circuit to indicate a
normal start.
Wide Open Throttle (WOT) Switch
This is a mechanically operated electrical switch controlled by throttle position to indicate a wide open throttle condition.
Coolant Temperature Switch
This is a dual function switch, controlled by engine coolant temperature. The switch is integral with the intake manifold heater control switch. When
open, the switch indicates that the engine is cold.
4 Inches Hg. Vacuum Switch, Except 4-150
This switch is controlled by ported vacuum from the carburetor and has a normally closed electrical contact which indicates a closed throttle
condition. The switch opens when vacuum drops below 4 inches Hg.
10 Inches Hg Vacuum Switch Except 4-150
This switch is controlled by manifold vacuum and opens when vacuum drops below 10 inches Hg, indicating a deep throttle condition.
4 Inches Hg Vacuum Switch, 4-150
This switch is controlled by ported vacuum and has a normally open electrical contact when vacuum level is less than 4 inches Hg. When vacuum
level reaches or exceeds 4 inches Hg, the switch closes and indicates to the MCU when a closed or partial throttle occurs.
10 Inches Hg Vacuum Switch, 4-150
This switch is controlled by manifold vacuum and has a normally closed electrical contact when vacuum is less than 10 inches Hg. when vacuum level
reaches or exceeds 10 inches Hg, the switch opens and indicates to the MCU when a part throttle or medium throttle condition occurs.
Closed Throttle Switch, 4-150
This switch is an integral part of the Sole-Vac throttle positioner and is attached to the vacuum actuator. When the throttle is in the closed position,
this electrical switch indicates to the MCU a closed throttle position.
Distributor, 4-150 & 6-258
The MCU will advance or retard ignition timing as necessary for the proper engine operating condition according to tach voltage input provided by
the distributor.
Knock Sensor
This sensor is a tuned piezoelectric crystal transducer located in the cylinder head. It provides an electrical signal to the MCU that is created by engine
detonation. Vibration from engine knock produces an electrical signal through this sensor, which relays to the MCU to retard ignition timing of any
single cylinder or any combination of cylinders, eliminating the knock condition.
MCU Outputs
Upstream & Downstream Solenoids
The upstream and downstream solenoids are located on a bracket attached to the left inner front fender panel. These solenoids are controlled by the
MCU and distribute air to either the catalytic converter or the exhaust pipe. For the CEC system to operate properly, all related systems and components
must be operational.
Idle Relay
The MCU energizes the idle relay, which in turn energized the idle solenoid, which allows vacuum to operate the Sole-Vac vacuum actuator.
Idle Solenoid
The idle solenoid allows the vacuum to operate the Sole-Vac vacuum actuator, which is used to increase idle speed. The idle solenoid is actuated by
the MCU by means of the idle relay.
