Grand Cherokee 2WD L6-4.0L VIN S (1997)
Powertrain Control Module: Description and Operation
Modes of Operation
Description of Operating Modes
MODES OF OPERATION
As input signals to the Powertrain Control Module (PCM) change, the PCM adjusts its response to the output devices. For example, the PCM
must calculate different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT).
The PCM will operate in two different modes: Open Loop and Closed Loop.
During Open Loop modes, the PCM receives input signals and responds only according to preset PCM programming. Input from the Oxygen
(O2S) sensors is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor the O2S sensors input. This input indicates to the PCM whether or not the calculated injector
pulse width results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the
O2S sensor, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine
performance.
The fuel injection system has the following modes of operation:
-
Ignition switch ON
-
Engine start-up (crank)
-
Engine warm-up
-
Idle
-
Cruise
-
Acceleration
-
Deceleration
-
Wide open throttle (WOT)
-
Ignition switch OFF
The ignition switch On, engine start-up (crank), engine warm-up, acceleration, deceleration and wide open throttle modes are Open Loop modes.
The idle and cruise modes, (with the engine at operating temperature) are Closed Loop modes.
Acceleration Mode
ACCELERATION MODE
This is an Open Loop mode. The Powertrain Control Module (PCM) recognizes an abrupt increase in throttle position or Manifold Absolute Pressure
(MAP) pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased
throttle opening.
Cruise Mode
CRUISE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At cruising speed, the Powertrain Control Module (PCM) receives inputs
from:
-
Air conditioning select signal (if equipped)
-
Air conditioning request signal (if equipped)
-
Battery voltage
-
Engine Coolant Temperature Sensor (CTS)
