1993 DODGE TRUCK Service Repair Manual

14-78
FUEL SYSTEM

• 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 evaporator switch opens, (indicating that evapo­
rator
is not in
proper temperature range),
PCM
will
not receive
the A/C
request signal.
The PCM
will
then remove
the
ground from
the A/C
relay, deacti­
vating
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.
3).
It is
used
to power
a
circuit
to the
generator field winding.
TORQUE
CONVERTER

CLUTCH RELAY A/C
CLUTCH RELAY
.
STARTER RELAY
AUTO
SHUTDOWN
RELAY
FUEL PUMP RELAY
DATA
LINK
CONNECTOR
POWERTRAIN
CONTROL
MODULE
J9314-164
Fig.
3
Relay Location—Typical

BATTERY VOLTAGE-PC! INPUT
The battery input provides power
to
operate
the

PCM. Battery voltage
is
needed
to
keep
PCM
mem­
ory alive.
The
memory stores diagnostic trouble code (DTC) messages
and the
minimum
TPS
value from
the previous key-on,
BRAKE
SWITCH-PCM INPUT

If
the PCM
receives
a
brake switch input while
the

speed control system
is on, it
will disable speed con­
trol.

CHARGE AIR TEMPERATURE SENSOR—PCM INPUT
The charge
air
temperature sensor
is
located
on top

of
the
intake manifold
(Fig. 4). It
provides
an
input
to
the PCM
that indicates
air
temperature
in the
manifold. Based
on the
charge
air
temperature input,
the
PCM
determines
if and how
long
to
energize
the
air intake heaters. Refer
to Air
Intake Heaters
in

this section. AIR

TEMPERATURE
SWITCH

(KSB
SOLENOID)

j9114-235

Fig.
4
Charge
Air
Temperature Sensor

ENGINE
SPEED
SENSOR-PCM
INPUT
The engine speed sensor (sometimes referred
to as

the crankshaft position sensor)
is
mounted
to the

front
of
engine
(Fig. 5). It
generates
an rpm
signal
to

the
PCM. The
engine speed sensor input
is
used along with
the
vehicle speed sensor
and
throttle
po­

sition sensor inputs
to
determine when
to
shift
the

automatic transmission into
and out of
overdrive.
The speed sensor signal
is
also used
as an
input
for
the
ASD
relay
(for
control
of
generator field), vehicle speed control
and
instrument panel mounted tachom­
eter.

SENSOR
MOUNTING BOLTS
VIBRATION
DAMPER
J9214-69

Fig.
5
Engine Speed Sensor
IGNITION
SENSE-PCM
INPUT
The ignition circuit
(J2)
sense input informs
the

PCM that
the
ignition switch
is in the run
position.

•

FUEL SYSTEM
14-79
OVERDRIVE/OVERRIDE SWITCH-PCM
INPUT

The overdrive/override switch is not used with
manual transmissions. On vehicles equipped with overdrive, the PCM reg­
ulates the 3-4 overdrive upshift and downshift
through the overdrive solenoid. An override switch is located on the instrument panel. The overdrive/override switch is a momentary con­
tact switch. The switch contacts are normally open. When the switch is activated, the PCM will receive a ground signal. The transmission will not enter over­
drive when the operator presses the override switch.
The transmission downshifts if the operator presses
the override switch while in overdrive.
COOLANT TEMPERATURE SENSOR The coolant temperature sensor is not used with
manual transmissions.
The coolant temperature sensor (Fig. 6) monitors
engine coolant temperature. This input is used to in­
hibit transmission upshift into overdrive when the
engine coolant temperature is below 16 degrees C (60
degrees F).

Fig.
6 Coolant
Temperature
Sensor

TRANSMISSION THERMO-SWITCH The transmission thermo-switch is not used with
manual transmissions.
The transmission thermo-switch opens when the
transmission fluid temperature is above 134°C (273°F). When the thermo-switch opens, the trans­
mission will not shift into overdrive. The transmis­ sion downshifts if it is in overdrive when the thermo-
switch opens. Once the thermo-switch opens, it will
not close until transmission fluid temperature drops
to 116°C (240°F). The switch is located in the trans­ mission-to-radiator cooling line (Fig. 7).

PARK/NEUTRAL SWITCH-PCM
INPUT
The park/neutral switch (Fig. 8) is located on the
automatic transmission housing. It provides an input
THERMO SWITCH
J9214-62

Fig.
7
Transmission
Thermo-Switch—Typical to the PCM. The input indicates if the automatic
transmission is in park, neutral or a drive gear se­ lection.
If transmission is in overdrive and operator shifts
vehicle into neutral, the overdrive solenoid will be de-energized. Normal PCM operation will resume
when the transmission is shifted back into drive po­ sition.
The PCM uses the park/neutral switch input when
determining speed control strategy. The PCM will
disable the speed control if the operator shifts the
transmission into neutral. The speed control will
have to be reset once the vehicle is placed back into drive.
The park/neutral switch is sometimes referred to as
the neutral safety switch. Refer to Group 21 Trans­ missions for adjustment, replacement and test infor­
mation.

Fig.
8 Park/Neutral Switch—Typical

POWER
GROUND-PCM
INPUT
Provides a common ground for power devices (sole­
noid and relay).

14 - 80
FUEL SYSTEM

•
SCI
RECEIVE-PCM
INPUT

The serial communication interface (SCI) receive
and transmit outputs allow the PCM to communicate
with the DRB II scan tool.

SENSOR
RETURN-PCM
INPUT
Sensor return provides a low noise ground refer­
ence for all system sensors.

SIGNAL
GROUND-PCM
INPUT
Provides a common ground for the input signals.

SPEED
CONTROL-PCM
INPUT
The PCM regulates the speed control system based
on inputs it receives. The speed control operating
range is from 35 to 85 mph. Inputs that effect speed control operation are:
• Park/neutral switch
• Vehicle speed sensor
• Throttle position sensor
• Engine speed sensor
• Brake switch

THROTTLE
POSITION SENSOR (TPS) —PCM
INPUT
The throttle position sensor is not used with man­
ual transmissions. The throttle position sensor (TPS) is mounted on
the top of the fuel injection pump (Fig. 9). The TPS
provides an input to the PCM. It senses how far the
throttle is open (past the idle position). The PCM uses the TPS input, along with vehicle speed sensor and engine speed sensor inputs to determine 3-4 up­
shift (overdrive) and 4-3 downshift. The TPS is a potentiometer. The PCM supplies 5
volts to the sensor. TPS output to the PCM varies
from approximately 1.0 volt at idle to 3.5 volts at
wide open throttle (WOT). T

J9114-237

Fig.
9
Throttle
Position
Sensor
VEHICLE SPEED SENSOR-PCM
INPUT
The vehicle speed sensor (Fig. 10) is located in the
extension housing of the transmission (2WD) or on the transfer case extension housing (4WD). A signal
is sent from this sensor, along with signals from both
the TPS and the engine speed sensor, to the PCM.
The PCM will then use this information to determine
when to shift into and out of overdrive.
The speed sensor is also used in determining speed
control set, decelerate, accelerate, maximum set
speed (85 mph) and minimum set speed (35 mph) op­
erations.
VEHICLE

SPEED

SENSOR

Fig.
10 Vehicle
Speed
Sensor—Typical Location

WATER-IN-FUEL SENSOR-PCM
INPUT
The water-in-fuel (WIF) sensor is located at the
bottom of the fuel/water separator filter (Fig. 11). The sensor sends an input to the PCM when it senses
water in the fuel. The PCM looks at the water-in-fuel sensor signal when the ignition key is put in the ON
position. It also monitors the input at the end of the intake heater post-heat cycle. The PCM turns the water-in-fuel indicator lamp to
the ON position if water is detected in the fuel. The
water-in-fuel indicator lamp is located in the instru­ ment panel.
J91 14-85

Fig.
11 Water-in-Fuel
Sensor

•

FUEL
SYSTEM
14-81
AIR
CONDITIONING
(A/C)
CLUTCH RELAY—PCM
OUTPUT
The PCM activates the A/C compressor through the
A/C clutch relay. The PCM regulates A/C compressor
operation by switching the ground circuit for the A/C
clutch relay on and off. The relay is located in the engine compartment (Fig. 3). By switching the ground path for the relay on and
off, the PCM is able to cycle the A/C compressor
clutch. This is based on changes in engine operating
conditions. If, during A/C operation, the PCM senses
a low idle speed, it will de-energize the relay. This
prevents A/C clutch engagement. The relay will re­ main de-energized until the idle speed increases.

GENERATOR
FIELD-PCM
OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. It will control
ASD relay operation. The input (through the PCM)
for the ASD relay comes from the engine speed sen­ sor. When engine running speed is above 384 rpm, a
signal is sent from the PCM to engage the ASD re­
lay. This supplies the necessary generator field wind­
ing control. When rpm drops below 320, the signal to
the ASD relay is stopped. Refer to Group 8A, for charging system information.

AIR INTAKE HEATER RELAYS-PCM
OUTPUT
The PCM operates the air intake heaters through
the air intake heater relays (Fig. 12). The relays may
be energized before and after cranking, depending upon intake manifold air temperature. The PCM
monitors intake manifold air temperature through
the charge air temperature sensor. Refer to Air In­
take Heaters in this section. The relays are not energized during engine crank­
ing. When they are energized they make a clicking
noise.

CAUTION:
Do not energize the air intake heater re­
lays
more than
once
per 15
minutes.
If the relays
are
cycled
and the key is turned off and then turned
back
on, the engine
could
be
damaged.
Wait 15

minutes
before
turning the key back to the ON po­

sition.

AIR INTAKE
HEATER
When energized, the air intake heaters warm in­
coming air as it enters the intake manifold. The air
intake heaters (Fig. 13) are energized by the PCM
through the air intake heater relays. Intake manifold air temperature determines when the heaters are en­
ergized. They may be energized before cranking and
after cranking, or both. Refer to Pre-Heat Cycle and
Post-Heat Cycle. The heaters are not energized dur­ ing cranking.
HEATER

RELAYS

WELL
J9114-67

Fig.
12 Air Intake Heater
Relays

Fig.
13 Air Intake Heaters—Typical PREHEAT CYCLE
The PCM powers up when the ignition key is
turned to the On position. If intake manifold air tem­
perature is 15°C (59°F) or below, the intake heaters are energized and the wait-to-start light is illumi­
nated. The heaters are energized for a specific amount of time. This is based on the intake manifold
air temperature. Refer to the Air Intake Heater Cy­
cle Chart.
Once the heaters have cycled, the wait-to-start
light goes out. While the engine is cranked, the heat­
ers are not energized.

POST-HEAT CYCLE
After engine has been started, the post-heat cycle
will begin if intake manifold air temperature was 15°C (59°F) or below when ignition switch was
turned on. Depending upon intake manifold temper­ ature, either: both heaters are energized, or they are
cycled on and off (when one is energized, the other is

not).
The time the heaters are energized depends upon intake manifold air temperature. Refer to the
Air Intake Heater Cycle Chart.

14 - 82
FUEL 'SYSTEM
—. — ~—— — «

INTAKE HEATER CYCLE CHART

Intake
featperafwre
Preheat
Cycle
Time

Ignition
l£ey ON

Engine
Not
Running
Pestheat
Cycle

Ignition
Key ON
Snglne Running

Above
15
°C
(59
°F)
0 Seconds
No

-8°C(18°F)to
15°C (59
°F)
10
Seconds

Yes

-17°C(1
°F)
-9
°C(]6°F)
15
Seconds
Yes

«2d°C(-15°F)
to-18°C(0
°F) 17.5
Seconds
Yes

Below-26
°C (-15
*F)
20 Seconds

Yes

J9114-239
AUTO SHUT DOWN (ASD) RELAY-PCM OUTPUT
The ASD relay is located in the engine compart­
ment (Fig. 14).
TORQUE CONVERTER
CLUTCH RELAY A/C CLUTCH RELAY STARTER RELAY
AUTO SHUTDOWN RELAY FUEL PUMP RELAY DATA LINK
CONNECTOR
POWERTRAIN

CONTROL MODULE
J9314-164

Fig.
14 Relay Location—Typical The ASD relay supplies battery voltage to the gen­
erator field winding to provide regulation of the
charging system. The ground circuit for the ASD re­
lay is controlled by the PCM. The PCM operates the
relay by switching the ground circuit on and off.

MALFUNCTION INDICATOR LAMP-PCM OUTPUT
The malfunction indicator lamp (formerly referred
to as the check engine lamp) illuminates at the bot­
tom of the instrument panel each time the ignition
key is turned on. It will stay on for three seconds as
a bulb test. If the powertrain control module (PCM) receives an
incorrect signal, or no signal from certain sensors or emission related systems, the lamp is turned on. This
is a warning that the PCM has recorded a system or
sensor malfunction. In some cases, when a problem is
declared, the PCM will go into a limp-in mode. This is an attempt to keep the system operating. It signals
an immediate need for service.
The lamp can also be used to display a diagnostic
trouble code (DTC). Cycle the ignition switch
On-Off-
On-Off-On within three seconds and any codes stored
in the PCM memory will be displayed. This is done
in a series of flashes representing digits. Refer to On-
Board Diagnostics in the General Diagnosis section
of this group for more information.

OVERDRIVE
INDICATOR LAMP-PCM OUTPUT
Indicates the state of the overdrive defeat switch
on the instrument panel.

OVERDRIVE
S0LEN0ID-PCM OUTPUT
The overdrive solenoid is used on vehicles that
have an automatic transmission. The solenoid is op­ erated by the PCM. It controls shifting in and out of
overdrive through the overdrive solenoid. Refer to Group 21 for overdrive solenoid service.

SCI
TRANSMIT—PCM OUTPUT
SCI Transmit is the serial data communication
transmit circuit for the DRB II scan tool. The PCM
transmits data to the DRB II through the SCI Trans­
mit circuit.

SPEED
C0NTR0L-PCM OUTPUT
The speed control vacuum and vent solenoids are
operated by the PCM. The vacuum solenoid main­
tains vacuum at a required pressure to resume, set or accelerate the speed control system. The vent so­
lenoid allows vacuum to bleed off during decelera­
tion, when the brakes are applied, or the
transmission is shifted into park or neutral.

TACHOMETER-PCM
OUTPUT
This output generates the necessary signal needed
to operate a dealer installed tachometer (if equipped).
The input for this signal is from the engine speed sensor.

WAIT-TO-START LAMP-PCM OUTPUT
The wait-to-start lamp is turned on and off by the
PCM based on the charge air temperature sensor in­
put. The light is turned on when the ignition is first ac­
tivated. It will remain on for two seconds as a bulb
test. If the PCM reads intake manifold air tempera­
ture below 15°C (59°F), it will turn the wait-to-start light on for the intake heater preheat cycle. The
light stays on until the preheat cycle is over. The wait-to-start light will flash on and off if the
charge air temperature sensor input to the PCM is

•

FUEL SYSTEM
14 - 83 below minimum value or above maximum value. The
PCM stores a DTC when these conditions occur.

WATER-IN-FUEL LAMP-PCM
OUTPUT
The water-in-fuel lamp is turned on and off by the
PCM. The lamp is turned on by the PCM when it re­ ceives an input from the water-in-fuel sensor. The sensor sends an input to the PCM when it detects
water in the fuel/water separator filter.

FUEL DRAIN MANIFOLD
Some fuel is continually vented from the injection
pump to cool the pump and the fuel injectors. During injection, a small amount of fuel flows past the injector nozzle and is not injected
into the combustion chamber. This fuel, along with
the fuel vented from the injection pump, drains into
the fuel drain manifold (Fig. 15). Fuel in the drain manifold is routed back to the fuel tank.

Fig.
15
Fuel
Drain Manifold

FUEL
HEATER
The 5.9L turbo-diesel engine has a fuel heater to
prevent the fuel from waxing in the fuel/water sepa­ rator. The fuel heater is located in the top of the fil­
ter/separator adapter (Fig. 16). The heater has a built in monitor that senses fuel
temperature. Voltage to operate the fuel heater is supplied through the ignition switch. The heater op­
erating range is from 6° - 13.5°C (43° - 53°F).

FUEL
INJECTION PUiVSP
The injection pump is a Bosch VE Distributor type
(Fig. 17). The injection pump is driven by the engine
camshaft. A gear on the end of the pump shaft
meshes with the camshaft gear. The pump is timed
to the engine. Fuel injection occurs near the end of the compression stroke for each cylinder. Refer to In­
jection Pump Removal and Installation in the Diesel Service Procedures section of this group for injection
pump timing procedures.
Fig.
16
Fuel
Heater

Fig.
17 Injection
Pump

The injection pump varies injector timing to corre­
spond with changing engine speed. As engine speed
increases, the internal pump pressure increases. Fuel
flows through an orifice in the advance mechanism
piston (Fig. 18). The piston is opposed by a spring.
The spring regulates injection pump timing advance.
As pump pressure increases, the piston moves against the spring, advancing injection timing. The
spring holds the advance mechanism in the starting
position during cranking and idle.
The mechanical lift pump delivers fuel under a low
pressure of 21-35 kPa (3-5 psi) to the injection pump
through the fuel/water separator filter. The injection
pump supplies high pressure fuel of approximately 59,000 kPa (8,000 psi) to each injector in precise me­
tered amounts at the correct time.
The injection pump contains the KSB (cold start)
solenoid, fuel solenoid, turbo boost control line and
manual shut down valve.

PISTON

ORIFICE

J9114-33

Fig.
18 injection Pump Timing Advance Mechanism

FUEL INJECTORS
The fuel injectors are mounted on the left side of
the cylinder head (Fig. 19). The injectors are con­
nected to the fuel injection pump by the high pres­ sure fuel lines.
HIGH PRESSURE
FUEL LINE
(6)
J9114-74
=
Fig.
19
Fuel
Injectors The injectors consist of the nozzle holder, O-ring
water seal, shims, spring, needle valve and nozzle (Fig. 20). Fuel enters the injector at the fuel inlet
(top of injector) and is routed, to the needle valve

bore.
When fuel pressure rises to approximately 24,445 kPa (3550 psi), the needle valve spring ten­
sion is overcome. The needle valve rises and fuel
flows through the spray holes in the nozzle tip into
the combustion chamber. The pressure required to lift the needle valve is the operating pressure set­
ting, sometimes referred to as the POP pressure set­ ting.
Fuel pressure in the injector circuit decreases after
injection. The injector needle valve is immediately
closed by the needle valve spring and fuel flow into
the combustion chamber is stopped. Exhaust gases are prevented from entering the injector nozzle by
the needle valve. HIGH
PRESSURE
FUEL FROM
INJECTION PUMP J91 14-82

Fig.
20
Fuel
Injector Operation

FUEL SOLENOID
The fuel solenoid (Fig. 21) is mounted on the injec­
tor pump. When energized, the solenoid allows fuel
to reach the high pressure chamber of the injection
pump.

FUEL

SOLENOID Fig.
21
Fuel
Solenoid

Battery voltage is supplied to the solenoid when
the ignition key is in the ON position. When ener­ gized, the solenoid pulls a plunger off its seat allow­
ing fuel to flow to the high pressure head of the injection pump. When the ignition key is turned to
the OFF position, the solenoid is not energized and
the plunger blocks the flow of fuel to high pressure chamber.
A minimum of ten volts is required to allow the so­
lenoid to lift the plunger off its seat. A minimum of six volts is required to hold the plunger in the open
position.

FUEL/WATER SEPARATOR FILTER
The fuel/water separator filter protects the injec­
tion pump by removing water and contaminants from
the fuel. The separator filter construction allows fuel

•

FUEL SYSTEM
14-85 to pass through it, but prevents moisture (water)
from doing so. Moisture collects at the bottom of the
separator filter.

WARNING:
EXTINGUISH
ALL
SMOKING
MATERI­
ALS
BEFORE
DRAINING
THE
FUEL/WATER
SEPA­
RATOR
FILTER.

There is a drain at the bottom of the separator fil­
ter (Fig. 16). Place a drain pan under the drain tube.
With the engine not running, push up on the drain
to remove the water from the separator filter. Hold
the drain open until all water and contaminants
have been removed and clean fuel exits the drain. Dispose of mixture in drain pan according to applica­
ble regulations.
Refer to the maintenance schedules in Group 0 in
this manual for the recommended fuel/water separa­
tor filter replacement intervals.

KSB
SOLENOID
The KSB solenoid is not an output of the PCM. The
solenoid is located on the injector pump (Fig. 22). It
contains a valve that controls venting of the injection
pump internal pressure regulator. When voltage is supplied to the solenoid, it closes off the vent circuit
in the injection pump. When the vent circuit is closed
off, internal pump pressure increases and injection
timing advances. The KSB solenoid allows the injec­
tion pump timing to reach full advance sooner. When the KSB solenoid is energized, internal
pump pressure reaches 8 bars (116 psi). When the so­ lenoid is not energized, internal pump pressure should be approximately 4 bars (58 psi). The KSB solenoid circuit contains an air tempera­
ture switch. Battery voltage is supplied to the sole­
noid through the ignition switch. The air temperature switch is mounted on the in­
take manifold next to the charge air temperature sensor (Fig. 23). The air temperature switch is open at or above 32°C (90°F).
Fig.
22 KSB
Solenoid—
Typical
Fig.
23 Air
Temperature
Switch

MANUAL SHUT DOWN LEVER
The injection pump has a manual shut down lever
(Fig. 24). In an emergency, the engine can be shut
down by turning the lever counterclockwise.

Fig.
24 Manual
Shut
Down
Lever

HIGH
PRESSURE FUEL LINES
CAUTION:
High pressure
fuel
lines must
be
held
se­

curely
in
place
in the
holders.
The
lines cannot con­

tact
each other
or
other components.
Do not
attempt
to
weld high pressure
fuel
lines
or to
repair lines
that
are
damaged. Only use
the
recommended
lines when replacement
of
high pressure
fuel
line
is

necessary.

High pressure fuel lines deliver fuel under pressure
of approximately 59,000 kPa (8,000 psi) from the in­
jection pump to the fuel injectors. The lines expand and contract from the high pressure fuel pulses gen­
erated during the injection process. All high pressure
fuel lines are of the same length and inside diameter. Correct high pressure fuel line usage and installation
is critical to smooth engine operation.