Definitions for Open/Closed Loop Operation:
POWERTRAIN CONTROL MODULE (PCM)
The Powertrain Control Module (PCM) is located in the engine compartment. The PCM is referred to as
JTEC (Jeep/Truck Engine Controller).
The PCM is a pre -programmed, triple microprocessor digital computer. The PCM operates the fuel system,
regulates ignition timing, air-fuel ratio, emission control devices, charging system, certain transmission
features, speed control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt
its programming to meet changing operating conditions.
The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM
regulates various engine and vehicle operations through different system components. These components
are referred to as Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs
to the PCM are considered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm,
manifold absolute pressure, engine coolant temperature, throttle position, transmission gear selection
(automatic transmission), vehicle speed and the brake switch.
The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle
speed, transmission gear selection, engine coolant temperature and from inputs it receives from the air
conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator
charge rate through control of the generator field and provides speed control operation.
PCM.....
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