Dodge RAM TRUCK 1500 1995 Service Manual page 1134

14 - 52 COMPONENT DESCRIPTION/SYSTEM OPERATION—EXCEPT DIESEL
B R
increased engine output and vehicle acceleration. The
PCM increases injector pulse width in response to in­
creased throttle opening.
DECELERATION MODE
When the engine is at operating temperature, this
is an Open Loop mode. During hard deceleration, the
powertrain control module (PCM) receives the follow­
ing inputs.
© Air conditioning request signal (if equipped)
• Battery voltage
© Engine coolant temperature sensor
• Crankshaft position sensor
• Intake manifold air temperature sensor
® Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
@ Camshaft position sensor signal (in the distribu­
tor)
• Park/Neutral switch (gear indicator signal—auto,
trans, only)
If the vehicle is under hard deceleration with the
proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM
will enter a fuel cut-off strategy in which it will not
supply battery voltage to the injectors. If a hard de­
celeration does not exist, the PCM will determine the
proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust en­
gine idle speed through the idle air control (IAC) mo­
tor.
The PCM adjusts ignition timing by turning the
ground path to the coil(s) on and off.
The PCM opens the ground circuit to the A/C
clutch relay to disengage the A/C compressor clutch.
This is done until the vehicle is no longer under de­
celeration (if the A/C system is operating).
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open
throttle operation, the powertrain control module
(PCM) receives the following inputs.
• Battery voltage
• Crankshaft position sensor
• Engine coolant temperature sensor
• Intake manifold air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distribu­
tor)
During wide open throttle conditions, the following
occurs:
© Voltage is applied to the fuel injectors with the
powertrain control module (PCM). The PCM will
then control the injection sequence and injector pulse
width by turning the ground circuit to each individ­
ual injector on and off. The PCM ignores the oxygen
sensor input signal and provides a predetermined
amount of additional fuel. This is done by adjusting
injector pulse width.
• The PCM adjusts ignition timing by turning the
ground path to the coil(s) on and off.
• The PCM opens the ground circuit to the A/C
clutch relay to disengage the A/C compressor clutch.
This will be done for approximately 15 seconds (if the
air conditioning system is operating).
If the vehicle has a manual transmission, the up­
shift lamp is operated by the PCM.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position,
the PCM stops operating the injectors, ignition
coil(s), ASD relay and fuel pump relay.