1993 DODGE TRUCK Service Repair Manual

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.

•

FUEL
SYSTEM
14 - 41

THROTTLE
BODY
FUEL
RAIL

CONNECTING
HOSES

THROTTLE
BODY

MOUNTING
BOLTS
J9214-31

Fig.
18
Throttle
Body
MOUNTING
SCREWS

MAP
SENSOR

RUBBER
FITTING

J9314-87

Fig.
19 Air Control
Passage

FUEL
RAIL
The fuel rail supplies fuel to the injectors and is
mounted to the intake manifold (Fig. 20). On vehi­
cles equipped with a 3.9L or 5.2L engine, the fuel
pressure regulator is attached to the rail and the fuel
pressure test port is integral with the rail. On vehi­ cles equipped with a 5.9L engine, the fuel pressure
regulator is not part of the fuel rail. It is located on
the fuel tank mounted fuel pump module. The fuel
rail is not repairable.

FUEL
PRESSURE
REGULATOR

3.9L/5.2L On vehicles equipped with a 3.9L or 5.2L engine,
the fuel pressure regulator is integral with the fuel
rail.
J9214-32

Fig.
20
Fuel
Rail—Typical Regulator Operation: The fuel pressure regulator
is a mechanical device that is not controlled by the
powertrain control module (PCM).
The fuel pressure regulator used is a vacuum bal­
anced, nonadjustable type. The regulator is mounted
on the output end of the fuel rail and is connected to
intake manifold vacuum (Figs. 21 or 22). The fuel re­
turn tube (to the fuel tank) is connected to the fuel
pressure regulator.
MAP

SENSOR
docc EL
PRESSURE
REGULATOR

„
VACUUM
LINE

REGULATOR

PROTECTIVE
CAP

J9214-26

Fig.
21
Fuel
Pressure
Regulator—3.9L
Engine
The regulator is calibrated to maintain fuel system
operating pressure at approximately 214 kPa (31

psi).
This is with vacuum applied while the engine is at idle. Fuel pressure will be 55-69 kPa (8-10 psi)
higher if vacuum is not applied to the regulator.
The pressure regulator contains a diaphragm, cali­
brated spring and a fuel return valve. Fuel pressure operates on one side of the regulator, while spring

VACUUM
LINE
PROTECTIVE
CAP
INTERNAL
FUEL FILTER FUEL
PRESSURE
REGULATOR FUEL RAIL
CONNECTOR
HOSES
J9214-27

Fig.
22
Fuel
Pressure
Regulator—5.2L
Engine
pressure
and
intake manifold vacuum operate
on the

other side. Spring pressure
on one
side
of the
dia­
phragm tries
to
force
the
return valve closed. Fuel
pressure
on
other side
of
diaphragm, with assistance from manifold vacuum
on
spring side
of
diaphragm, act against spring pressure
to
open
the
return valve.
System fuel pressure
is the
amount
of
fuel pressure
required
to
force against spring pressure
and
unseat
the return valve.
Without vacuum applied
to the
spring side
of the

regulator,
the
spring
is
calibrated
to
open
the
fuel
re­

turn outlet. This happens when
the
pressure differen­
tial between
the
fuel injectors
and the
intake
manifold reaches approximately
269 kPa (39 psi).

Since manifold vacuum varies with engine operating
conditions,
the
amount
of
vacuum applied
to the

spring side
of the
diaphragm varies.
For
this reason,
fuel pressure varies, depending upon intake manifold
vacuum. With
low
vacuum, such
as
during wide open
throttle conditions, minimal vacuum assistance
is
available. Full spring pressure
is
exerted
to
seal
the

fuel outlet. This causes
the
system pressure
to in­

crease. With high vacuum, such
as at
engine idle
or

during vehicle deceleration, fuel pressure
on one
side
of
the
diaphragm
is
balanced
by
intake manifold
pressure. This
is
done
on the
spring side
of the
dia­
phragm
and
results
in
lower system fuel pressure.
5.9L
ENGINE
On vehicles equipped with
a 5.9L
engine,
the
fuel
filter and fuel pressure regulator
are one
combined
part
(Fig. 23). The
fuel filter/fuel pressure regulator is located
on the top of the
fuel pump module
(Fig.

24).
It is
pressed into
a
rubber grommet
on
module (Fig.
23).
Regulator Operation:
The
fuel pressure regulator
RUBBER
GROMMET AT PUMP MODULE FUEL FILTER/FUEL
PRESSURE REGULATOR
CALIBRATED SPRINGS
X
EXCESS FUEL BACK
TO TANK
FUEL INLET J9314-170

Fig.
23
Side
View—Filter/Regulator—5.9L
Engine

LOCKNUT FUEL SUPPLY
TUBE FUEL FILTER/
FUEL PRESSURE REGULATOR PUMP/GAUGE

ELEC.
CONNECTION
PRESSURE RELIEF/
, I I

ROLLOVER VALVE
J9314-167
Fig.
24
Filter/Regulator Location—5.9L
Engine

is
a
mechanical device that
is not
controlled
by the

powertrain control module (PCM).
The regulator
is
calibrated
to
maintain fuel system
operating pressure
at
approximately 241-310
kPa

(35-45
psi).
The regulator contains
a
diaphragm, calibrated
springs
and a
fuel return valve.
The
internal fuel fil­
ter
(Fig. 23) is
part
of the
assembly. Fuel
is
supplied
by the
electric fuel pump through
an opening tube
at the
bottom
of
filter/regulator
(Fig.
23).
The
calibrated pressure regulator allows
a
con­
stant fuel system operating pressure
of
approxi­
mately 241-310
kPa
(35-45
psi).
Fuel flows through
regulator
and
fuel filter
and on to
fuel injectors
at
engine. If
the
fuel pressure
at
regulator exceeds approxi­
mately
45 psi, an
internal diaphragm closes
and ex­
cess fuel pressure
is
routed back into pump module and returned
to
fuel tank
(Fig. 23).

MULTI-PORT
FUEL
INJECTION
(MPI)—GENERAL DIAGNOSIS—EXCEPT DIESEL

INDEX

page

Camshaft Position Sensor Testing
............
52
Charge
Air
Temperature Sensor Test
52

Coolant Temperature Sensor Test
52

Crankshaft Position Sensor Test
54

Diagnostic Trouble Code (DTC)
60

DRB
II
Scan
Tool
........................
60

Fuel
Injector
Test
57

Fuel Pump Pressure Test
57
Idle
Air
Control
(IAC) Motor Test
55

Manifold Absolute Pressure (MAP) Sensor Test
. 53
page

On-Board
Diagnostics (OBD)
59

Oxygen
(02)
Sensor Heating Element Test
54
Powertrain
Control
Module (PCM) 60-Way Connector
. 47

Relays—Operation/Testing
56

Starter
Motor Relay Test
57

System
Schematics
. 47

Throttle
Position Sensor (TPS) Test
54

Visual Inspection
43

VISUAL
INSPECTION
A visual inspection
for
loose, disconnected,
or
incor­
rectly routed wires
and
hoses should
be
made. This should
be
done before attempting
to
diagnose
or
ser­
vice
the
fuel injection system.
A
visual check will
help spot these faults
and
save unnecessary test
and
diagnostic time.
A
thorough visual inspection will
in­

clude
the
following checks: (1) Verify that
the
60-way connector
is
fully
in­

serted into
the
connector
of the
powertrain control
module
(PCM) (Fig. 1).
Verify that
the
connector
mounting screw
is
tightened
to 4 N#m (35 in. lbs.)
torque.
PCM
MOUNTING
BOLTS

PCM CONNECTOR CONNECTOR MOUNTING BOLT
J9314-165

Fig.
1
Powertrain Control
Module
(PCM) (2) Inspect
the
battery cable connections.
Be
sure
that they
are
clean
and
tight.
(3) Inspect fuel pump relay
and air
conditioning
compressor clutch relay
(if
equipped). Inspect
the

ASD relay connections. Inspect starter motor relay connections. Inspect relays
for
signs
of
physical dam­
age
and
corrosion.
The
relays
are
located
in the en­

gine compartment
(Fig. 2).
TORQUE CONVERTER
CLUTCH RELAY
A/C
CLUTCH RELAY STARTER RELAY
AUTO SHUTDOWN RELAY FUEL PUMP RELAY POWERTRAIN
DATA UNK CONTROL
CONNECTOR MODULE
J9314-164

Fig.
2
Relay Location (4) Inspect ignition coil connections. Verify that
coil secondary cable
is
firmly connected
to
coil (Fig.
3

or 4).
|X COIL

frCONNECTOR J9214-7

Fig.
3
Ignition Coil—3.9U5.2L/5.9L
LDC-Gas
Engine

14 - 44
FUEL
SYSTEM

•

Fig.
4 ignition Coil—5.9L
HDC-Gas
Engine
(5) Verify that distributor cap is correctly attached
to distributor. Be sure that spark plug cables are
firmly connected to the distributor cap and the spark
plugs are in their correct firing order. Be sure that coil cable is firmly connected to distributor cap and
coil. Be sure that camshaft position sensor wire con­
nector (at the distributor) is firmly connected to har­
ness connector. Inspect spark plug condition. Refer to Group 8D, Ignition. Connect vehicle to an oscillo­
scope and inspect spark events for fouled or damaged
spark plugs or cables.
(6) Verify that generator output wire, generator
connector and ground wire are firmly connected to
the generator. (7) Inspect the system body grounds for loose or
dirty connections. Refer to Group 8, Wiring for
ground locations. (8) Verify positive crankcase ventilation (PCV)
valve operation. Refer to Group 25, Emission Control System for additional information. Verify PCV valve
hose is firmly connected to PCV valve and manifold (Fig. 5).
Fig.
5 PCV
Valve
Hose
Connections—Typical (9) On 3.9L and 5.2L engines, verify that vacuum
hose is firmly connected to fuel pressure regulator and manifold fitting (Figs. 6 or 7).

CONNECTOR
HOSES
J9214-27

Fig.
7
Pressure
Regulator
Vacuum
Hose—5.2L
Engine

(10) Inspect fuel* tube quick-connect fitting-to-fuel
rail connections. (11) Verify that hose connections to all ports of
vacuum fittings on intake manifold are tight and not leaking.

•

FUEL
SYSTEM
14-45 (12) Inspect accelerator cable, transmission throt­
tle cable (if equipped) and cruise control cable con­
nections (if equipped). Check their connections to the
throttle arm of throttle body for any binding or re­ strictions (Fig. 8).

Fig.
8
Throttle
Body
Cables—Typical
(13) If equipped with vacuum brake booster, verify
that vacuum booster hose is firmly connected to fit­
ting on intake manifold. Also check connection to
brake vacuum booster.
(14) Inspect the air cleaner inlet and air filter ele­
ment for dirt or restrictions.
(15) Inspect radiator grille area, radiator fins and
air conditioning condenser for restrictions. (16) Verify that the intake manifold charge air
temperature sensor wire connector is firmly con­ nected to harness connector (Figs. 9 or 10).

Fig.
9 Air
Temperature
Sensor—3.9L
(V-6)
Engine
(17) Verify that MAP sensor electrical connector is
firmly connected to MAP sensor (Fig. 11). Also verify
that rubber L-shaped fitting from MAP sensor to the
throttle body is firmly connected (Fig. 12).
(18) Verify that fuel injector wire harness connec­
tors are firmly connected to injectors in the correct
Fig.
10 Air
Temperature
Sensor—5.2U5.9L
(V-8)

Engines
MANIFOLD
ABSOLUTE

Fig.
11 MAP Sensor—Typical
order. Each harness connector is numerically tagged
with the injector number (INJ 1, INJ 2 etc.) of its
corresponding fuel injector and cylinder number.
(19) Verify harness connectors are firmly con­
nected to idle air control (IAC) motor, throttle posi­
tion sensor (TPS) and manifold absolute pressure (MAP) sensor (Fig. 11).
(20) Verify that wire harness connector is firmly
connected to the engine coolant temperature sensor (Fig. 13).
(21) Raise and support the vehicle.
(22) Verify that oxygen sensor wire connector (or
connectors) are firmly connected to the sensor (or sensors). Inspect sensor(s) and connector(s) for dam­age (Figs. 14 or 15).