Dodge ram truck 3500 1996 Service Manual page 1261

BR FUEL SYSTE1 14 - 27
G E N E R A L I N F O R M A T I O N
(Continued)
The PCM monitors the crankshaft position sensor.
I f the PCM does not receive a crankshaft position
sensor signal within 8 seconds of cranking the
engine, It will shut down the fuel injection system.
The fuel pump is activated by the PCM through
the fuel pump relay.
Voltage is applied to the fuel injectors with the
PCM. The PCM will then control the injection
sequence and injector pulse width by turning the
ground circuit to each individual injector on and off.
The PCM determines the proper ignition timing
according to input received from the crankshaft posi­
tion sensor.
ENGINE WARM-UP MODE
This Is an Open Loop mode. During engine warm-
up, the powertrain control module (PCM) receives
inputs from:
• 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)
• Park/neutral switch (gear indicator signal—auto,
trans, only)
• Air conditioning select signal (if equipped)
• Air conditioning request signal (if equipped)
Based on, these inputs 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 adjusts engine idle speed through the
idle air control (IAC) motor and adjusts ignition tim­
ing.
• The PCM operates the A/C compressor clutch
through the clutch relay. This is done i f A/C has been
selected by the vehicle operator and requested by the
A/C thermostat.
• When engine has reached operating tempera­
ture, the PCM will begin monitoring 02S sensor
input. The system will then leave the warm-up mode
and go into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this
is a Closed Loop mode. At idle speed, the powertrain
control module (PCM) receives inputs from:
• Air conditioning select signal (if equipped)
• Air conditioning request signal (if equipped)
• 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)
• Battery voltage
• Park/neutral switch (gear indicator signal—auto,
trans, only)
• Oxygen sensors
Based on these inputs, the following occurs:
• Voltage is applied to the fuel injectors with the
powertrain control module (PCM). The PCM will
then control injection sequence and injector pulse
width by turning the ground circuit to each individ­
ual injector on and off.
• The PCM monitors the 0 2 S sensor input and
adjusts air-fuel ratio by varying injector pulse width.
It also adjusts engine idle speed through the idle air
control (IAC) motor.
• The PCM adjusts ignition timing by increasing
and decreasing spark advance.
• The PCM operates the A/C compressor clutch
through the clutch relay. This happens i f A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.
CRUISE MODE
When the engine is at operating temperature, this
is a Closed Loop mode. At cruising speed, the power-
train control module (PCM) receives inputs from:
• Air conditioning select signal (if equipped)
© 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)
• Oxygen (02S) sensors
Based on these inputs, the following occurs:
• Voltage is applied to the fuel injectors with the
PCM. The PCM will then adjust the injector pulse
width by turning the ground circuit to each individ­
ual injector on and off.
• The PCM monitors the 02S sensor input and
adjusts air-fuel ratio. I t also adjusts engine idle
speed through the idle air control (IAC) motor.
• The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
• The PCM operates the A/C compressor clutch
through the clutch relay. This happens i f A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.