coolant temperature DODGE TRUCK 1993 Service Service Manual

9
- 12
ENGINES

•
CONDITION

POSSIBLE
CAUSES
CORRECTION

EXCESSIVE
EXHAUST

SMOKE
(Cont'd)
More
than
one
sealing washer
under an injector.
Check
and remove
extra
washer.
Improperly operating injectors.
Check
and replace inoperative injectors.
Improperly operating or over-
fueled injection pump.
Replace
injection pump.

Piston
rings
not sealing
(blue smoke). Perform blow-by check. Correct as required.

ENGINE
WILL
NOT

SHUT-OFF
Fuel shutoff valve inoperative.

Engine
running on fumes drawn into the air intake.
Stop
the engine mechanically
with
lever on the
fuel
pump.

Check/replace
sealing washer, piston and
spring.

Check
the air intake ducts for the source of the fumes.
WARNING:
In
ease
of engine runaway due to flammable
fumes

from gasoline spills or turbocharger oil leaks
being
sucked
into the
engine,
shut off engine ignition switch first then use a CO* or dry
chemical type
fire
extinguisher
and direct the
spray
under
the
front
bumper to
remove
oxygen
supply. The engine air
intake
is on the

passenger
side
behind the bumper. The
fire
extinguisher
must
bo
directed at this location for emergency shutdown conditions.

COOLANT
TEMPERA­

TURE
ABOVE
NORMAL
Low
coolant level.
(a) Check coolant level. Add coolant, if necessary.
(b) Locate and correct the source of the coolant leak. Refer to
troubleshooting
logic for coolant
loss.

Incorrect/improperly operating

pressure
cap.
Replace
cap
with
the correct rating for the
system.

High
lube oil level.
Check/drain
oil to correct level.

Loose
drive belt on water

pump/fan.
Check/replace
belt or belt tensioner.
Inadequate air flow to the radiator. Check/repair radiator core, fan shroud and fan clutch as
required.

Radiator
fins
plugged.
Blow
debris from fins.

Collapsed
radiator
hose.
Replace
the
hose.

Improperly operating tempera­

ture
sensor/gauge.
Verify
that
the
gauge
and temperature
sensor
are accurate.

Replace
gauge/sensor,
if bad.
Improperly operating, incorrect

or
no thermostat.
Check
and replace the thermostat.

Air
in the cooling
system.
(a) Make sure the
fill
rate
is not being exceeded and the correct
vented thermostat is installed.
(b) Check for loose hose
clamps.
Tighten if
loose.

(c) If aeration continued, check for a
compression
leak through the head gasket.
Inoperative water pump.
Check
and replace the water pump.
incorrect injection pump timing. Verify pump timing marks are aligned. Check/time the injector

pump
(refer
to Group 7,
Cooling
System).
J9209-56
SERVICE DIAGNOSIS (DIESEL ENGINE) - PERFORMANCE (CONT.)

•

ENGINES
9 - 13

CONDITION
POSSIBLE
CAUSES
COfiiiECTION

COOLANT
TEMPERA­

TURE
ABOVE
NORMAL
(Cont'd)
Overfueled injection pump.

Plugged
cooling
passages
in
radiator, head, head gasket or

block.

Engine
overloaded.
Replace
the injection
pump.

Flush
the
system
and
fill
with
clean coolant.
Verify
that
the engine load rating is not being exceeded.

COOLANT
TEMPERA­

TURE
BELOW
NORMAL
Too
much air flow
across
the
radiator.
Incorrect thermostat, broken
thermostat jiggle pin or

contamination
in thermostat.
Temperature
sensor
or
gauge
inoperative.

Coolant
not flowing by
temperature
sensor.
Check/repair
viscous
fan as required.

Check
and replace thermostat.
Verify
that
the
gauge
and
sensor
are accurate. If not, replace

gauge/sensor.

Check
and clean coolant
passages.

J9109-254
SERVICE DIAGNOSIS (DIESEL ENGINE) • PERFORMANCE (CONT.)

•
• —
ENGINES
9 - 15
CONDITION

POSSIBLE CAUSES
CORRECTION

LUBRICATING
OIL

PRESSURE
TOO
HIGH
Pressure
switch/gauge
not

operating
properly.
Verify
the
pressure
switch
is
functioning
correctly.
If not,

replace
switch/gauge.

Engine
running
too
cold.
Refer
to
Coolant
Temperature
Below
Normal
(Engine
Diagnosis-

Performance)

Oil
viscosity
too thick. Make
sure
the
correct
oil Is
being
used.
Refer
to
Group
O,

Lubrication
and
Maintenance.

Oil
pressure
regulator
valve

stuck
closed
or
binding.
Check
and replace valve, and/or oil cooler cover.

LUBRICATING
OIL
LOSS
External
leaks.
Visually
inspect for oil
leaks.
Repair as required.

Crankcase
being
overfilled. Verify that the correct dipstick is being
used.

incorrect
oil specification or

viscosity.
(a) Make sure the correct oil is being
used.

(b)
Look
for reduced
viscosity
from dilution with fuel.
(c) Review/reduce the oil
change
intervals.
Oil
cooler
leak.
Check
and replace the oil cooler.

High
blow-by
forcing oil out
the breather.
Check
the breather tube area for
signs
of oil
loss.
Perform the
required repairs.

Turbocharger
leaking
oil to the
air intake.
Inspect
the air
ducts
for evidence of oil transfer.

Repair
as required.

Worn
valve
seals.
Inspect
and replace the valve
seals.

Piston
rings
not
sealing
(oil

being
consumed
by the
engine).
Perform
blow-by check. Repair as required.

COMPRESSION
KNOCKS
Air in the
fuel
system.

Poor
quality
fuel.
Bleed
the fuel
system
(refer
to
Group
14, Fuel
System).

Verify by operating from a temporary tank with
good
fuel. Clean

and
flush the fuel
supply
tanks.
Replace fuel/water separator

filter.

Engine
overloaded. Verify that engine load rating is not being exceeded.
Incorrect injection
pump
timing.
Check
and time injection pump
(refer
to
Group
14, Fuel
System).

Improperly
operating
injectors.
Check
and replace inoperative injectors. J9109-266 SERVICE DIAGNOSIS (DIESEL ENGINE) - MECHANICAL (CONT.)

•

FUEL
SYSTEM
14-29
MULTI-PORT
FUEL
INJECTION
(MPI)-COMPONENT DESCRIPTION/SYSTEM
OPERATION-EXCEPT DIESEL

INDEX

page

Air
Conditioning (A/C) Clutch
Relay-Pern
Output
. 35

Air
Conditioning (A/C)
Controls—PCM
Input
.... 31

Auto
Shut
Down
(ASD)
Relay-PCM
Output
. ... 36

Automatic
Shut
Down
(ASD)
Sense-PCM
Input
. 31
Battery
Voltage-PCM
Input
32

Brake
Switch-PCM
Input
32

Camshaft
Position
Sensor—PCM
Input
32

Charge
Air
Temperature
Sensor—PCM
Input
. . . 32

Crankshaft
Position
Sensor-PCM
Input
.......
32
Electric
Exhaust
Gas Recirculation Transducer
(EET)
Solenoid-PCM
Output
...
.......
36

Engine
Coolant Temperature
Sensor—PCM
Input
. 33

EVAP
Canister
Purge
Solenoid—PCM
Output
. . . 37

Fuel
Injectors-PCM Output
37
Fuel
Pressure
Regulator
41

Fuel
Rail
41

General
Information
.......................
29

Generator
Field-PCM
Output
36

Generator
Lamp-PCM
Output
36
Idle
Air
Control
(IAC)
Motor-PCM
Output
......
36

Ignition
Circuit
Sense—PCM
Input
33

GENERAL
INFORMATION
All
gas
powered engines
are
equipped with sequen­
tial Multi-Port Fuel Injection (MPI).
The MPI
system (Fig.
1)
provides precise air/fuel ratios
for all
driving
conditions. The Powertrain Control Module
(PCM)
operates
the fuel system.
The PCM was
formerly referred
to
as
the
SBEC
or
engine controller.
The PCM is a
pre­
programmed, dual microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission
control devices, charging system, speed control,
air
conditioning compressor clutch engagement
and
idle speed.
The PCM can
adapt
its
programming
to
meet
changing operating conditions.
Powertrain Control Module (PCM) Inputs rep­
resent
the
instantaneous engine operating conditions.
Air-fuel mixture
and
ignition timing calibrations
for

various driving
and
atmospheric conditions
are
pre­
programmed into
the PCM. The PCM
monitors
and
analyzes various inputs.
It
then computes engine fuel
and ignition timing requirements based
on
these
in­

puts.
Fuel delivery control
and
ignition timing will
then
be
adjusted accordingly. Other inputs
to the
PCM
are
provided
by the
brake
light switch,
air
conditioning select switch
and the

speed control switches.
All
inputs
to the PCM are

converted into signals. Electrically operated fuel injectors spray fuel
in

precise metered amounts into
the
intake port directly above
the
intake valve.
The
injectors
are
fired
in a

specific sequence
by the PCM. The PCM
maintains
page

Ignition
Coil-PCM
Output
37

Malfunction Indicator
Lamp—PCM
Output
37

Manifold
Absolute
Pressure
(MAP)
Sensor-
PCM
Input
33

Open
Loop/Closed
Loop
Modes
of
Operation
. . . 38

Overdrive/Override
Switch
34

Oxygen
(02)
Sensor—PCM
Input
33

Park/Neutral
Switch—PCM
Input
34

Power
Ground
34

Powertrain Control Module
(PCM)
30

SCI
Receive-PCM
Input
. 34

SCI
Transmit-PCM
Output
37

Sensor
Return
—PCM
Input
35

Shift Indicator-PCM Output
38

Speed
Control-PCM
Input
34
Speed
Control-PCM
Output
38

SRI
Lamp-PCM
Output
36

Tachometer—PCM
Output
38

Throttle
Body
40

Throttle
Position
Sensor
(TPS)-PCM
Input
35

Vehicle
Speed
Sensor-PCM
Input
35

an air/fuel ratio
of 14.7 to 1 by
constantly adjusting
injector pulse width. Injector pulse width
is the

length
of
time that
the
injector opens
and
sprays fuel into
the
chamber.
The PCM
adjusts injector pulse
width
by
opening
and
closing
the
ground path
to the
injector.
Manifold absolute pressure
(air
density)
and
engine
rpm (speed)
are the
primary inputs that determine
fuel injector pulse width.
The PCM
also monitors
other inputs when adjusting air-fuel ratio.
Inputs That Effect Fuel Injector Pulse Width:
• Exhaust
gas
oxygen content
• Coolant temperature
• Manifold absolute pressure (MAP)
• Engine speed
• Throttle position
• Battery voltage •
Air
conditioning selection
• Transmission gear selection (auto, trans.)
• Speed control The powertrain control module (PCM) adjusts igni­
tion timing
by
controlling ignition coil operation.
The

ignition coil receives battery voltage when
the
igni­
tion
key is in the run or
starter (crank) position.
The

PCM provides
a
ground
for the
ignition coil.
The
coil
discharges when
the PCM
supplies
a
ground.
By
switching
the
ground path
on and off, the PCM
reg­
ulates ignition timing.
The sensors
and
switches that provide inputs
to the

powertrain control module
(PCM)
comprise
the En-

14
- 30
FUEL
SYSTEM

INPUTS

OUTPUTS
POWERTRAIN
CONTROL
MODULE
DRB
II

SCAN
TOOL

SPEED

CONTROL

BRAKE

SWITCH
A/C
LOW

PRESSURE
CUTOFF
SWITCH VEHICLE

SPEED
SENSOR PARK/NEUTRAL
SWITCH TORQUE CONVERTER
CLUTCH SOLENOID
MALFUNCTION

INDICATOR
LAMP
m
HEATED
i

*OXYGEN SENSOR ENGINE
COOLANT
yy
BATTERY
TEMPERATURE

SENSOR
MAP SENSOR

i—r
CHARGE
AIR
TEMPERATURE
SENSOR
AIR CHARGE
TEMPERATURE
SENSOR
DISTRIBUTOR

WITH
CAMSHAFT
r
POSITION
SENSOR
(|
TACHOMETER

A/C
CLUTCH RELAY
AUTO
SHUTDOWN
RELAY OVERDRIVE
SOLENOID
IDLE AIR
CONTROL MOTOR
SPEED

CONTROL
SHIFT

INDICATOR

LAMP

EMISSION

CONTROL SOLENOIDS
IGNITION
COIL
OVERDRIVE
OVERRIDE SWITCH
ASD

SENSE
FUEL
INJECTORS
PARK
THROTTLE

SOLENOID
GENERATOR CRANKSHAFT
POSITION FUEL
PUMP
RELAY
J9314-117

Fig.
1 Multi-Port
Fuel
Injection
Components—Except
Diesel

gine Control System. It is also comprised of the PCM Outputs (engine control devices that the are operated
by the PCM).

SYSTEM DIAGNOSIS
The powertrain control module (PCM) tests many
of its own input and output circuits. If a diagnostic
trouble code (DTC) is found in a major system, this information is stored in the PCM memory. Refer to
On-Board Diagnostics in the Multi-Port Fuel Injec­
tion—General Diagnosis—Except Diesel section of
this group for DTC information.

POWERTRAIN
CONTROL MODULE (PCM)
The Powertrain Control Module (PCM) (Fig. 2) op­
erates the fuel system. The PCM was formerly re­
ferred to as the SBEC or engine controller. The PCM is a pre-programmed, dual microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system, speed con­trol, air conditioning compressor clutch engagement
A/C
CLUTCH RELAY STARTER RELAY
TORQUE CONVERTER CLUTCH RELAY
AUTO
SHUTDOWN RELAY
FUEL PUMP RELAY
DATA UNK
CONNECTOR
POWERTRAIN

CONTROL MODULE
J9314-164

Fig.
2 Powertrain Control
Module
(PCM) Location 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

•

FUEL SYSTEM
14-31 through different system components. These compo­
nents are referred to as Powertrain Control Module
(PCM) Outputs. The sensors and switches that pro­
vide inputs to the PCM are considered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon in­
puts it receives from sensors that react to: engine rpm, manifold absolute pressure, engine coolant tem­
perature, throttle position, transmission gear selec­
tion (automatic transmission), vehicle speed and the
brake switch.
The PCM adjusts idle speed based on inputs it re­
ceives 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 gener­
ator charge rate through control of the generator
field and provides speed control operation.
Powertrain Control Module (PCM) Inputs:
• Generator output • A/C request (if equipped with factory A/C)
• A/C select (if equipped with factory A/C)
• Auto shut down (ASD) sense
• Charge air temperature sensor
• Battery voltage
• Brake switch
• Engine coolant temperature sensor
• Crankshaft position sensor • Ignition circuit sense (ignition switch in run posi­
tion)
• Manifold absolute pressure (MAP) sensor
• Overdrive/override switch
• Oxygen sensor(s)
• Park/neutral switch (auto, trans, only)
• SCI receive (DRB II connection) • Speed control resume switch
• Speed control set switch • Speed control on/off switch
• Camshaft position sensor signal
• Throttle position sensor
• Vehicle speed sensor
• Sensor return
• Power ground
• Signal ground Powertrain Control Module (PCM) Outputs:
• A/C clutch relay
• Idle air control (IAC) motor
• Auto shut down (ASD) relay
• Generator field
• Malfunction indicator lamp
• Service reminder indicator lamp
• EGR valve control solenoid • Fuel injectors
• Fuel pump relay
• Ignition coil • EVAP canister purge solenoid
• SCI transmit (DRB II connection)
• Shift indicator lamp (manual transmission only)
• Speed control vacuum solenoid
• Speed control vent solenoid
• Tachometer (on instrument panel, if equipped) The powertrain control module (PCM) contains a
voltage convertor. This converts battery voltage to a
regulated 8.0 volts. It is used to power the crankshaft
position sensor and camshaft position sensor. The
PCM also provides a five (5) volt supply for the man­ ifold absolute pressure (MAP) sensor and throttle po­
sition sensor (TPS).

AIR
CONDITIONING
(A/C)
CONTROLS-PCM
INPUT
The A/C control system information applies to fac­
tory installed air conditioning units. A/C SELECT SIGNAL: When the A/C switch is
in the ON position and the A/C low pressure switch
is closed, an input signal is sent to the powertrain
control module (PCM). The signal informs the PCM
that the A/C has been selected. The PCM adjusts idle speed to a pre-programmed rpm through the idle air
control (IAC) motor to compensate for increased en­
gine load. A/C REQUEST SIGNAL: Once A/C has been se­
lected, the powertrain control module (PCM) receives
the A/C request signal from the evaporator switch.
The input indicates that the evaporator temperature is in the proper range for A/C application. The PCM
uses this input to cycle the A/C compressor clutch (through the A/C relay). It will also determine the
correct engine idle speed through the idle air control (IAC) motor position. If the A/C low pressure switch opens (indicating a
low refrigerant level), the PCM will not receive an
A/C select signal. The PCM will then remove the ground from the A/C relay. This will deactivate the
A/C compressor clutch. If the evaporator switch opens, (indicating that
evaporator is not in proper temperature range), the
PCM will not receive the A/C request signal. The
PCM will then remove the ground from the A/C re­ lay, deactivating the A/C compressor clutch.

AUTOMATIC SHUT DOWN
(ASD)
SENSE-PCM INPUT
A 12 volt signal at this input indicates to the PCM
that the ASD has been activated. The ASD relay is located in the engine compartment (Fig. 2). It is used
to connect the oxygen sensor(s) heater element, igni­
tion coil, generator field winding and fuel injectors to 12 volt + power supply. This input is used only to sense that the ASD relay
is energized. If the powertrain control module (PCM)
does not see 12 volts at this input when the ASD
should be activated, it will set a diagnostic trouble
code (DTC).

•

FUEL SYSTEM
14 - 33 Refer to Group 8D, Ignition System for more crank­
shaft position sensor information. The engine will not operate if the PCM does not re­
ceive a crankshaft position sensor input.

ENGINE
COOLANT TEMPERATURE SENSOR-PCM
INPUT
The engine coolant temperature sensor is installed
next to the thermostat housing (Fig. 6) and protrudes
into the water jacket. The sensor provides an input
voltage to the powertrain control module (PCM) re­
lating coolant temperature. The PCM uses this input
along with inputs from other sensors to determine in­
jector pulse width and ignition timing. As coolant temperature varies, the coolant temperature sensor
resistance will change. This change in resistance re­sults in a different input voltage to the PCM. When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.

Fig.
6 Coolant
Temperature
Sensor—
Typical

IGNITION CIRCUIT
SENSE-PCM
INPUT
The ignition circuit sense input tells the power-
train control module (PCM) the ignition switch has
energized the ignition circuit. Refer to the wiring di­
agrams for circuit information.

MANIFOLD ABSOLUTE
PRESSURE
(MAP)

SENSOR-PCM
INPUT
The MAP sensor reacts to absolute pressure in the
intake manifold. It provides an input voltage to the
powertrain control module (PCM). As engine load changes, manifold pressure varies. The change in
manifold pressure causes MAP sensor voltage to
change. The change in MAP sensor voltage results in a different input voltage to the PCM. The input volt­
age level supplies the PCM with information about
ambient barometric pressure during engine start-up (cranking) and engine load while the engine is run­ ning. The PCM uses this input along with inputs
from other sensors to adjust air-fuel mixture.
The MAP sensor is mounted on the side of the en­
gine throttle body (Fig. 7). The sensor is connected to
the throttle body with a rubber L-shaped fitting.

MANIFOLD
ABSOLUTE
Fig.
7 Manifold
Absolute
Pressure
(MAP)
Sensor—
Typical

OXYGEN
(02)
SENSOR—PCM
INPUT
3.9L/5.2L/S»9L
LDC
ENGINE
The single 02 sensor on the 3.9L, 5.2L or 5.9L light
duty cycle (LDC) engine is located in the exhaust
down pipe (Fig. 8). It provides an input voltage to the
powertrain control module (PCM) relating the oxy­
gen content of the exhaust gas. The PCM uses this
information to fine tune the air-fuel ratio by adjust­ ing injector pulse width.
The 02 sensor produces voltages from 0 to 1 volt.
This voltage will depend upon the oxygen content of
the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean
air-fuel mixture), the sensor produces a low voltage.
When there is a lesser amount present (rich air-fuel
mixture) it produces a higher voltage. By monitoring
the oxygen content and converting it to electrical
voltage, the sensor acts as a rich-lean switch.
The oxygen sensor is equipped with a heating ele­
ment that keeps the sensor at proper operating tem­
perature during all operating modes. Maintaining
correct sensor temperature at all times allows the system to enter into closed loop operation sooner. In Closed Loop operation, the powertrain control
module (PCM) monitors the 02 sensor input (along
with other inputs). It then adjusts the injector pulse

14 - 38
FUEL SYSTEM

•
Fig.
17 Ignition Coil—5.9L
HDC-Gas
Engine

SHIFT INDICATOR-PCM
OUTPUT
Vehicles equipped with manual transmissions have
an Up-Shift indicator lamp. The lamp is controlled
by the powertrain control module (PCM). The lamp illuminates on the instrument panel to indicate when
the driver should shift to the next highest gear for
best fuel economy. The PCM will turn the lamp off after 3 to 5 seconds if the shift of gears is not per­
formed. The up-shift light will remain off until vehi­ cle stops accelerating and is brought back to range of
up-shift light operation. This will also happen if ve­
hicle is shifted into fifth gear. The indicator lamp is normally illuminated when
the ignition switch is turned on and it is turned off
when the engine is started up. With the engine run­
ning, the lamp is turned on/off depending upon en­
gine speed and load.

SPEED
CONTROL-PCM
OUTPUT
Speed control operation is regulated by the power-
train control module (PCM). The PCM controls the
vacuum to the throttle actuator through the speed
control vacuum and vent solenoids. Refer to Group
8H for Speed Control Information.

TACHOMETER—PCM
OUTPUT
The powertrain control module (PCM) supplies en­
gine rpm values to the instrument cluster tachome­ ter. Refer to Group 8E for tachometer information.

OPEN
LOOP/CLOSED LOOP 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). There
are several different modes of operation that deter­
mine how the PCM responds to the various input sig­
nals.
MODES

• Open Loop
• Closed Loop During Open Loop modes, the powertrain control
module (PCM) receives input signals and responds
only according to preset PCM programming. Input
from the oxygen (02) sensor(s) is not monitored dur­
ing Open Loop modes.
During Closed Loop modes, the PCM will monitor
the oxygen (02) sensor 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 ex­
haust oxygen content through the 02 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 tem­
perature) are Closed Loop modes.

IGNITION
SWITCH
(KEY-ON)
MODE
This is an Open Loop mode. When the fuel system
is activated by the ignition switch, the following ac­
tions occur:
• The powertrain control module (PCM) pre-posi-
tions the idle air control (IAC) motor. • The PCM determines atmospheric air pressure
from the MAP sensor input to determine basic fuel strategy.
• The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based
on this input.
• Intake manifold charge air temperature sensor in­
put is monitored.
• Throttle position sensor (TPS) is monitored. • The auto shut down (ASD) relay is energized by
the PCM for approximately three seconds. • The fuel pump is energized through the fuel pump
relay by the PCM. The fuel pump will operate for ap­
proximately one second unless the engine is operat­ ing or the starter motor is engaged.
• The 02 sensor(s) heater element is energized
through the fuel pump relay. The 02 sensor(s) input

•

FUEL SYSTEM
14 - 39 is not used by the PCM to calibrate air-fuel ratio
during this mode of operation,
• The up-shift indicator light is illuminated (manual
transmission only).
ENGINE
START-UP
MODE
This is an Open Loop mode. The following actions
occur when the starter motor is engaged.
The powertrain control module (PCM) receives in­
puts from:
• Battery voltage
• Engine coolant temperature sensor • Crankshaft position sensor
• Intake manifold charge air temperature sensor • Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Starter motor relay • Camshaft position sensor signal The PCM monitors the crankshaft position sensor.
If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the en­

gine,
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 se­ quence and injector pulse width by turning the
ground circuit to each individual injector on and off.
The PCM determines the proper ignition timing ac­
cording 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 in­
puts from:
• Battery voltage • Crankshaft position sensor
• Engine coolant temperature sensor
• Intake manifold charge air temperature sensor • Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS) • Camshaft position sensor signal (in the distributor)
• 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 if A/C has
been selected by the vehicle operator and requested by the A/C thermostat.
• If the vehicle has a manual transmission, the up­
shift light is operated by the PCM.
« When engine has reached operating temperature,
the PCM will begin monitoring 02 sensor(s) 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 charge air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distributor)
® Battery voltage
• Park/Neutral switch (gear indicator signal—Auto,

trans,
only) • Oxygen sensor
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 02 sensor(s) input and ad­
justs 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 if 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 charge air temperature sensor • Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distributor)

14
- 40
FUEL
SYSTEM

• • Park/Neutral switch (gear indicator signal—auto,

trans,
only)
• Oxygen (02) sensor(s) 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 02 sensor(s) input and ad­
justs air-fuel ratio. It 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 if A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.

ACCELERATION MODE
This is an Open Loop mode. The powertrain control
module (PCM) recognizes an abrupt increase in
throttle position or MAP pressure as a demand for
increased engine output and vehicle acceleration.
The PCM increases injector pulse width in response
to increased 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 select signal (if equipped)
• Air conditioning request signal (if equipped)
• Battery voltage
• Engine coolant temperature sensor
• Crankshaft position sensor
• Intake manifold charge air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distributor)
• 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 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 charge air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS) • Camshaft position sensor signal (in the distributor) 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 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 light 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,
ASD relay and fuel pump relay.

THROTTLE
BODY
Filtered air from the air cleaner enters the intake
manifold through the throttle body (Fig. 18). Fuel does not enter the intake manifold through the throt­
tle body. Fuel is sprayed into the manifold by the fuel injectors. The throttle body is mounted on the
intake manifold. It contains an air control passage (Fig. 19) controlled by an idle air control (IAC) mo­
tor. The air control passage is used to supply air for idle conditions. A throttle valve (plate) is used to supply air for above idle conditions. The throttle position sensor (TPS), idle air control
(IAC) motor and manifold absolute pressure sensor
(MAP) are attached to the throttle body. The acceler­
ator pedal cable, speed control cable and transmis­
sion control cable (when equipped) are connected to
the throttle arm. A (factory adjusted) set screw is used to mechani­
cally limit the position of the throttle body throttle
plate. Never attempt to adjust the engine idle speed using this screw. All idle speed functions are
controlled by the PCM.