Ground DODGE RAM 1500 1998 2.G Workshop Manual

(25) Confirm alignment of the replacement frame
rail tip. (Fig. 14)
(26) Final welding should be performed in a skip
(stitch) type method to minimize the heat buildup
and frame distortion, utilizing the Weld Process
Specifications at the end of this section. The pre-
ferred method is GMAW (MIG). (Refer to 13 -
FRAME & BUMPERS/FRAME - SPECIFICATIONS -
WELDING)
(a) Apply root pass welds to the root joint one
quadrant at a time, switching to the opposite side
of the frame for each quadrant. (Fig. 8)
(b) Clean the welds of any flux and other impu-
rities before proceeding with the cover pass welds.
(c) Apply the cover pass welds in the same man-
ner as described above.
(27) Confirm alignment of the replacement frame
rail tip. (Fig. 14)
NOTE: Any burned surface coatings will need to be
removed prior to application of corrosion preventa-
tive coatings.
(28) Dress the welded area and apply corrosion
resistant coatings inside and out.
(a) Apply etch-primer to the inside of the frame
rail repair area.
(b) Inside the rail, inject a creeping wax based
rust inhibitor compound through the existing holes
in the frame ensuring 100% coverage including the
space between the original frame rail and the rein-
forcing sleeve.
(c) Apply a durable top coat to the outside of the
repair area.
(29) Tighten the front cab mounting bolt to the
FESM bracket to 81 N´m (60 ft. lbs.).(30) Install the stabilizer bar. (Refer to 2 - SUS-
PENSION/FRONT/STABILIZER BAR - INSTALLA-
TION)
(31) Install the front bumper. (Refer to 13 -
FRAME & BUMPERS/BUMPERS/FRONT BUMPER
- INSTALLATION)
(32) Install the wire harness and ground strap if
previously removed and install the bolt.
(a) If necessary, re-drill and tap the ground
strap mounting hole
(33) Install the front wheelhouse splash shield.
(Refer to 23 - BODY/EXTERIOR/FRONT WHEEL-
HOUSE SPLASH SHIELD - INSTALLATION)
Fig. 13 RING FILLET WELD
1 - WELD START LOCATION
2 - WELD END LOCATION
3 - RING-FILLET WELD
Fig. 14 FRAME TIP DIMENSIONS
1 - PLP POINT
2 - FRAME
3 - PLP POINT
4 - REPLACEMENT FRAME TIP
DRFRAMES & BUMPERS 13 - 9
FRAME (Continued)

STANDARD PROCEDURE - HYDROFORM
FENDER RAIL REPAIR
CAUTION: This repair procedure assumes damage
to the right or left hydroform fender rail (Fig. 18).
Prior to any repairs, the vehicle must be mounted
on the appropriate frame repair equipment (ªframe
rackº), checked with three dimensional measuring
equipment, and necessary pull corrections made. If
damage exists in the hydroform fender rail, or cab
beyond the area covered by this service procedure
after dimensional corrections are made, the hydro-
form must be replaced in its entirety. Refer to 23 -
BODY/BODY STRUCTURE/WELD LOCATIONS -
SPECIFICATIONS, when replacing the entire hydro-
form.
(1) Before proceding with this repair procedure
review the required service warnings and precau-
tions. (Refer to 13 - FRAME & BUMPERS/FRAME -
WARNING)
(2) Disconnect and isolate the battery negative
cable.
(3) Remove the front wheelhouse splash shield.
(Refer to 23 - BODY/EXTERIOR/FRONT WHEEL-
HOUSE SPLASH SHIELD - REMOVAL)(4) Remove the fender. (Refer to 23 - BODY/EXTE-
RIOR/FRONT FENDER - REMOVAL)
(5) Remove the A/C condenser, if required. (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMB-
ING/A/C CONDENSER - REMOVAL)
(6) Remove the A/C lines, if required. Refer to the
Heating and Air Conditioning section of the manual
for recommended procedures.
(7) Remove the radiator assembly. (Refer to 7 -
COOLING/ENGINE/RADIATOR - REMOVAL)
(8) Remove the air cleaner and support bracket, if
required. (Refer to 9 - ENGINE/AIR INTAKE SYS-
TEM/AIR CLEANER ELEMENT - REMOVAL)
(9) Remove the integrated power module. (Refer to
8 - ELECTRICAL/POWER DISTRIBUTION/INTE-
GRATED POWER MODULE - REMOVAL)
(10) Remove the bolts and position aside the wire
harness and grounds, if required.
(11) Remove the upper radiator crossmember.
(Refer to 23 - BODY/EXTERIOR/UPPER RADIATOR
CROSSMEMBER - REMOVAL)
(12) Remove the headlamp unit. (Refer to 8 -
ELECTRICAL/LAMPS/LIGHTING - EXTERIOR/
HEADLAMP UNIT - REMOVAL)
(13) Remove the front cab mount to the Front End
Sheet Metal bracket (FESM) bolt.
Fig. 18 HYDROFORM FENDER RAILS
1 - HYDROFORM FENDER RAIL
2 - FRONT END SHEET METAL BRACKET
3 - UPPER RADIATOR CROSSMEMBER BOLTS (4)4 - UPPER RADIATOR CROSSMEMBER
5 - LOWER RADIATOR CROSSMEMBER BOLTS (8)
6 - LOWER RADIATOR CROSSMEMBER
DRFRAMES & BUMPERS 13 - 11
FRAME (Continued)

(14) Remove the bolts attaching the lower radiator
crossmember to the hydroform fender rail. (Fig. 18)
CAUTION: Do not use any flame or plasma cutting
equipment to cut the frame in this procedure. The
inaccurate and high temperatures achieved during
flame or plasma cutting will change the metal char-
acteristics and may weaken the frame and/or repair
location.
(15) Using a reciprocating saw or equivalent, cut
the fender rail and shotgun at a straight and square
section of the hydroform and remove.
(16) Smooth and square the cut edges.
(17) Using the damaged structure as a reference
cut the service part at the same location as the first
cut. Smooth and square the cut edges.
NOTE: The repair structure should butt up to the
remaining structure and provide the same overall
vehicle geometry.
(18) Fabricate 51 mm (2.0 in.) long repair inserts
using scrap from the old structure or the replacement
part. It will be necessary to split the inserts on each
of their four sides to fit into the hydroform.
(19) Remove any paint or e-coat from the inserts
and also to the interior and exterior of the hydro-
forms.
(20) Cut plug weld holes as described below.
²On the upper rail, cut one 13 mm (0.5 in.) hole
on each side of the rail, 25 mm (1.0 in.) from the butt
joint of the tubes.
²On the lower rail, cut one 13 mm (0.5 in.) hole
on the top and bottom sides of the rail 25 mm (1.0
in.) from the butt joint of the tube.
²On the lower rail, cut two 13 mm (0.5 in.) holes
on the inner and outer sides of the rail 25 mm (1.0
in.) from the butt joint of the tube.
CAUTION: Shield the surrounding area and compo-
nents from exposure to the welding spatter and
heat.
(21) Install the insert 1º into the replacement part
and tack into place with a weld. (Refer to 13 -
FRAME & BUMPERS/FRAME - SPECIFICATIONS -
WELDING)
(22) Insert the service part into place and using
the appropriate measuring equipment, verify the
front end sheet metal bracket's location in all three
(X,Y, and Z) planes of space. (Fig. 19)
(23) Complete all 360É plug welds.
NOTE: Before the final welding, use three dimen-
sional measuring equipment to ensure the part is in
the correct location. Verify that tap plate extrusion
at the bottom of the vertical post lines up with theisolator and hole in the frame perch mount. Also
ensure the lower radiator closure tube is bolted into
the forward shotgun ends.
(24) Complete welding by making a 360É butt weld
around the fender rails.
(25) Metal finish the exposed welds on the hydro-
forms.
(26) Dress the welded area and apply corrosion
resistant coatings inside and out.
(a) Inside the rail, inject a creeping wax based
rust inhibitor compound to the inside of the hydro-
forms ensuring 100% coverage including the mat-
ing face between the fender rail sections and insert
such that corrosion protection is restored in the
internal cavity.
(b) Apply a durable top coat to the outside of the
repair area.
(27) Install the front cab mount bolt if previously
removed and tighten to 81 N´m (60 ft. lbs.).
(28) Install the lower radiator crossmember bolts
and tighten to 28 N´m (21 ft. lbs.).
(29) Install the headlamp unit. (Refer to 8 - ELEC-
TRICAL/LAMPS/LIGHTING - EXTERIOR/HEAD-
LAMP UNIT - INSTALLATION)
(30) Install the upper radiator crossmember. (Refer
to 23 - BODY/EXTERIOR/UPPER RADIATOR
CROSSMEMBER - INSTALLATION)
(31) Install the wire harness and ground if previ-
ously removed and install the bolts.
(32) Install the integrated power module, if previ-
ously removed. (Refer to 8 - ELECTRICAL/POWER
DISTRIBUTION/INTEGRATED POWER MODULE -
INSTALLATION)
(33) Install the air cleaner bracket and air cleaner,
if previously removed. (Refer to 9 - ENGINE/AIR
INTAKE SYSTEM/AIR CLEANER ELEMENT -
INSTALLATION)
(34) Install the radiator assembly. (Refer to 7 -
COOLING/ENGINE/RADIATOR - INSTALLATION)
(35) Install the A/C lines, if previously removed.
Refer to the Heating and Air Conditioning section of
the manual for the recommended procedures.
(36) Install the A/C condenser, if previously
removed. (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING/A/C CONDENSER - INSTAL-
LATION)
(37) Install the fender. (Refer to 23 - BODY/EXTE-
RIOR/FRONT FENDER - INSTALLATION)
(38) Install the front wheelhouse splash shield.
(Refer to 23 - BODY/EXTERIOR/FRONT WHEEL-
HOUSE SPLASH SHIELD - INSTALLATION)
(39) Reconnect the battery ground.
13 - 12 FRAMES & BUMPERSDR
FRAME (Continued)

STANDARD PROCEDURE - REAR FRAME
H-SECTION REPLACEMENT
CAUTION: This procedure is designed to replace
the H-section/spare tire support located at the rear
of the frame assembly. Prior to any cutting, the
vehicle must be mounted on the appropriate frame
repair equipment (ªframe rackº), checked with three
dimensional measuring equipment, and the neces-
sary pull corrections made. If damage remains in
the frame beyond the area covered by this service
part after the pull, the frame must be replaced in its
entirety.
(1) Before proceding with this repair procedure
review the required service warnings and precau-
tions. (Refer to 13 - FRAME & BUMPERS/FRAME -
WARNING)
(2) Disconnect and isolate the battery negative
cable.
(3) Remove the cargo box. (Refer to 23 - BODY/EX-
TERIOR/CARGO BOX - REMOVAL)
(4) Remove the trailer hitch. (Refer to 13 - FRAME
& BUMPERS/FRAME/TRAILER HITCH -
REMOVAL)
(5) Raise and support the frame so the tires are off
floor.(6) Remove the shock absorbers. (Refer to 2 - SUS-
PENSION/REAR/SHOCK - REMOVAL)
(7) Remove the rear leaf spring shackle bolts and
let the axle rest on the ground. (Fig. 20)
(8) Remove the spare wheel.
Fig. 19 ENGINE COMPARTMENT/FRONT STRUCTURE
Fig. 20 REAR SPRING
1 - SPRING SHACKLE
2 - LEAF SPRING EYE BOLT/NUT
3 - REAR LEAF SPRING
DRFRAMES & BUMPERS 13 - 13
FRAME (Continued)

(26) Install the lower shock absorber bolts. (Refer
to 2 - SUSPENSION/REAR/SHOCK - INSTALLA-
TION)
(27) Install the trailer hitch. (Refer to 13 - FRAME
& BUMPERS/FRAME/TRAILER HITCH - INSTAL-
LATION)(28) Install the cargo box. (Refer to 23 - BODY/EX-
TERIOR/CARGO BOX - INSTALLATION)
(29) Reconnect the battery ground.
SPECIFICATIONS
SPECIFICATIONS - WELD PROCESS
CAUTION: All welds should conform to
DaimlerChrysler vehicle engineering process stan-
dard ªps 9472º.
WELDING PROCESS FLUX CORED ARC GAS METAL ARC (MIG)* SHIELDED METAL ARC
(STICK)
Material Thickness3.7 mm to 4.2 mm 3.7 mm to 4.2 mm 3.7 mm to 4.2 mm
Electrode TypeLincoln Electrical Co.
Product #: NR-211 MP
(Do Not Substitute)AWS ER70S-3
(Do Not Substitute)** AWS E 7018
Electrodes Size Inches.045 Tubular .035 Solid 3/329
Electrode Stick Out3/89- 1/291/29- 5/89N/A
PolarityElectrode9-9
Work Piece9+9Electrode9+9
Work Piece9-9Electrode9+9
Work Piece9-9
Shielding GasSelf Shielded 75% Ar
25% CO2Self Shielded
Gas Flow RateN/A 25 - 35 CFM N/A
Wire Feed Speed
(inches per minute)110 - 130 Vertical Down
70 - 90 Flat & Overhead245 - 250 Vertical Down
210 - 225 Flat &
OverheadN/A
Approximate Amperage
Vertical110 - 130 175 85 (3/329Diameter)
Flat & Overhead70 - 90 155 90 (3/329Diameter)
Voltage15-18 19-20 N/A
Direction of Welding
VerticalVertical Down Hill (only) Vertical Down Hill (only) Vertical - Up Hill (only)
Flat & OverheadFlat - Push or Drag Flat - Push or Drag Flat - Drag
*First choice - Gas Metal Arc Welding Process:Butt joints - apply two layers (passes) of weld metal. First pass
should only fill approximately
1¤2the thickness. Vertical position welds - maintain electrode wire at leading edge of
weld puddle while traveling down hill to produce maximum penetration into the sleeve. These techniques work for
FCAW as well.
**E7018new electrodes may be exposed to the atmosphere for up to ten hours with no harmful effect.
Reconditioning schedules should come from the manufacturer.
DRFRAMES & BUMPERS 13 - 15
FRAME (Continued)

stream. The spraying action atomizes the fuel, add-
ing it to the air entering the combustion chamber.
The nozzle (outlet) ends of the injectors are posi-
tioned into openings in the intake manifold just
above the intake valve ports of the cylinder head.
The engine wiring harness connector for each fuel
injector is equipped with an attached numerical tag
(INJ 1, INJ 2 etc.). This is used to identify each fuel
injector.
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage is supplied to the injectors through
the ASD relay.
The PCM determines injector pulse width based on
various inputs.
OPERATION - PCM OUTPUT
The nozzle ends of the injectors are positioned into
openings in the intake manifold just above the intake
valve ports of the cylinder head. The engine wiring
harness connector for each fuel injector is equipped
with an attached numerical tag (INJ 1, INJ 2 etc.).
This is used to identify each fuel injector with its
respective cylinder number.
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage (12 volts +) is supplied to the injec-
tors through the ASD relay. The ASD relay will shut-
down the 12 volt power source to the fuel injectors if
the PCM senses the ignition is on, but the engine is
not running. This occurs after the engine has not
been running for approximately 1.8 seconds.
The PCM determines injector on-time (pulse width)
based on various inputs.
REMOVAL
(1) Remove fuel rail. Refer to Fuel Injector Rail
Removal.
(2) Disconnect clip(s) that retain fuel injector(s) to
fuel rail (Fig. 12).
INSTALLATION
(1) Install fuel injector(s) into fuel rail assembly
and install retaining clip(s).(2) If same injector(s) is being reinstalled, install
new o-ring(s).
(3) Apply a small amount of clean engine oil to
each injector o-ring. This will aid in installation.
(4) Install fuel rail. Refer to Fuel Rail Installation.
(5) Start engine and check for fuel leaks.
FUEL PUMP RELAY
DESCRIPTION
The 5±pin, 12±volt, fuel pump relay is located in
the Power Distribution Center (PDC). Refer to the
label on the PDC cover for relay location.
OPERATION
The Powertrain Control Module (PCM) energizes
the electric fuel pump through the fuel pump relay.
The fuel pump relay is energized by first applying
battery voltage to it when the ignition key is turned
ON, and then applying a ground signal to the relay
from the PCM.
Whenever the ignition key is turned ON, the elec-
tric fuel pump will operate. But, the PCM will shut-
down the ground circuit to the fuel pump relay in
approximately 1±3 seconds unless the engine is oper-
ating or the starter motor is engaged.
Fig. 12 INJECTOR RETAINING CLIP
1 - PLIERS
2 - INJECTOR CLIP
3 - FUEL INJECTOR - TYPICAL
4 - FUEL RAIL - TYPICAL
DRFUEL INJECTION - GAS 14 - 27
FUEL INJECTOR (Continued)

REMOVAL
The fuel pump relay is located in the Power Distri-
bution Center (PDC) (Fig. 13). Refer to label on PDC
cover for relay location.
(1) Remove PDC cover.
(2) Remove relay from PDC.
(3) Check condition of relay terminals and PDC
connector terminals for damage or corrosion. Repair
if necessary before installing relay.
(4) Check for pin height (pin height should be the
same for all terminals within the PDC connector).
Repair if necessary before installing relay.
INSTALLATION
The fuel pump relay is located in the Power Distri-
bution Center (PDC). Refer to label on PDC cover for
relay location.
(1) Install relay to PDC.
(2) Install cover to PDC.
IDLE AIR CONTROL MOTOR
DESCRIPTION
A separate IAC motor is not used with the 5.7L V-8
engine.
The IAC stepper motor is mounted to the throttle
body, and regulates the amount of air bypassing the
control of the throttle plate. As engine loads and
ambient temperatures change, engine rpm changes.
A pintle on the IAC stepper motor protrudes into apassage in the throttle body, controlling air flow
through the passage. The IAC is controlled by the
Powertrain Control Module (PCM) to maintain the
target engine idle speed.
OPERATION
A separate IAC motor is not used with the 5.7L V-8
engine.
At idle, engine speed can be increased by retract-
ing the IAC motor pintle and allowing more air to
pass through the port, or it can be decreased by
restricting the passage with the pintle and diminish-
ing the amount of air bypassing the throttle plate.
The IAC is called a stepper motor because it is
moved (rotated) in steps, or increments. Opening the
IAC opens an air passage around the throttle blade
which increases RPM.
The PCM uses the IAC motor to control idle speed
(along with timing) and to reach a desired MAP dur-
ing decel (keep engine from stalling).
The IAC motor has 4 wires with 4 circuits. Two of
the wires are for 12 volts and ground to supply elec-
trical current to the motor windings to operate the
stepper motor in one direction. The other 2 wires are
also for 12 volts and ground to supply electrical cur-
rent to operate the stepper motor in the opposite
direction.
To make the IAC go in the opposite direction, the
PCM just reverses polarity on both windings. If only
1 wire is open, the IAC can only be moved 1 step
(increment) in either direction. To keep the IAC
motor in position when no movement is needed, the
PCM will energize both windings at the same time.
This locks the IAC motor in place.
In the IAC motor system, the PCM will count
every step that the motor is moved. This allows the
PCM to determine the motor pintle position. If the
memory is cleared, the PCM no longer knows the
position of the pintle. So at the first key ON, the
PCM drives the IAC motor closed, regardless of
where it was before. This zeros the counter. From
this point the PCM will back out the IAC motor and
keep track of its position again.
When engine rpm is above idle speed, the IAC is
used for the following:
²Off-idle dashpot (throttle blade will close quickly
but idle speed will not stop quickly)
²Deceleration air flow control
²A/C compressor load control (also opens the pas-
sage slightly before the compressor is engaged so
that the engine rpm does not dip down when the
compressor engages)
²Power steering load control
The PCM can control polarity of the circuit to con-
trol direction of the stepper motor.
Fig. 13 PDC LOCATION
1 - BATTERY
2 - INTEGRATED POWER MODULE (IPM)
14 - 28 FUEL INJECTION - GASDR
FUEL PUMP RELAY (Continued)

INTAKE AIR TEMPERATURE
SENSOR
DESCRIPTION
The 2±wire Intake Manifold Air Temperature (IAT)
sensor is installed in the intake manifold with the
sensor element extending into the air stream.
The IAT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as intake mani-
fold temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
The IAT sensor provides an input voltage to the
Powertrain Control Module (PCM) indicating the
density of the air entering the intake manifold based
upon intake manifold temperature. At key-on, a
5±volt power circuit is supplied to the sensor from
the PCM. The sensor is grounded at the PCM
through a low-noise, sensor-return circuit.
The PCM uses this input to calculate the following:²Injector pulse-width
²Adjustment of spark timing (to help prevent
spark knock with high intake manifold air-charge
temperatures)
The resistance values of the IAT sensor is the same
as for the Engine Coolant Temperature (ECT) sensor.
REMOVAL
3.7L V-6
The intake manifold air temperature (IAT) sensor
is installed into the left side of intake manifold ple-
num (Fig. 16).
(1) Disconnect electrical connector from IAT sen-
sor.
(2) Clean dirt from intake manifold at sensor base.
(3) Gently lift on small plastic release tab (Fig. 16)
or (Fig. 17) and rotate sensor about 1/4 turn counter-
clockwise for removal.
(4) Check condition of sensor o-ring.
4.7L V-8
The intake manifold air temperature (IAT) sensor
is installed into the left side of intake manifold ple-
num (Fig. 18).
(1) Disconnect electrical connector from IAT sen-
sor.
(2) Clean dirt from intake manifold at sensor base.
Fig. 15 IDLE AIR CONTROL MOTOR - 4.7L V-8
1 - THROTTLE BODY
2 - TPS
3 - IAC MOTOR
4 - IAT SENSOR
5 - MOUNTING SCREWS
Fig. 16 IAT SENSOR LOCATION - 3.7L V-6
1 - IAT SENSOR
2 - RELEASE TAB
3 - ELECTRICAL CONNECTOR
14 - 30 FUEL INJECTION - GASDR
IDLE AIR CONTROL MOTOR (Continued)

(3) Position sensor into intake manifold and rotate
clockwise until past release tab.
(4) Install electrical connector.
5.7L V-8
The intake manifold air temperature (IAT) sensor
is installed into the front of the intake manifold air
box plenum (Fig. 19).
(1) Check condition of sensor o-ring.
(2) Clean sensor mounting hole in intake manifold.
(3) Position sensor into intake manifold and rotate
clockwise until past release tab.
(4) Install electrical connector.
MAP SENSOR
DESCRIPTION
3.7L V-6
The Manifold Absolute Pressure (MAP) sensor is
mounted into the front of the intake manifold with 2
screws.
4.7L V-8
The Manifold Absolute Pressure (MAP) sensor is
mounted into the front of the intake manifold with 2
screws.
5.7L V-8
The Manifold Absolute Pressure (MAP) sensor is
mounted to the front of the intake manifold air ple-
num box.
OPERATION
The MAP sensor is used as an input to the Power-
train Control Module (PCM). It contains a silicon
based sensing unit to provide data on the manifold
vacuum that draws the air/fuel mixture into the com-
bustion chamber. The PCM requires this information
to determine injector pulse width and spark advance.
When manifold absolute pressure (MAP) equals
Barometric pressure, the pulse width will be at max-
imum.
A 5 volt reference is supplied from the PCM and
returns a voltage signal to the PCM that reflects
manifold pressure. The zero pressure reading is 0.5V
and full scale is 4.5V. For a pressure swing of 0±15
psi, the voltage changes 4.0V. To operate the sensor,
it is supplied a regulated 4.8 to 5.1 volts. Ground is
provided through the low-noise, sensor return circuit
at the PCM.
The MAP sensor input is the number one contrib-
utor to fuel injector pulse width. The most important
function of the MAP sensor is to determine baromet-
ric pressure. The PCM needs to know if the vehicle is
at sea level or at a higher altitude, because the air
density changes with altitude. It will also help to cor-
rect for varying barometric pressure. Barometric
pressure and altitude have a direct inverse correla-
tion; as altitude goes up, barometric goes down. At
key-on, the PCM powers up and looks at MAP volt-
age, and based upon the voltage it sees, it knows the
current barometric pressure (relative to altitude).
Once the engine starts, the PCM looks at the voltage
again, continuously every 12 milliseconds, and com-
pares the current voltage to what it was at key-on.
The difference between current voltage and what it
was at key-on, is manifold vacuum.
During key-on (engine not running) the sensor
reads (updates) barometric pressure. A normal range
can be obtained by monitoring a known good sensor.
As the altitude increases, the air becomes thinner
(less oxygen). If a vehicle is started and driven to a
very different altitude than where it was at key-on,
the barometric pressure needs to be updated. Any
time the PCM sees Wide Open Throttle (WOT), based
upon Throttle Position Sensor (TPS) angle and RPM,
it will update barometric pressure in the MAP mem-
ory cell. With periodic updates, the PCM can make
its calculations more effectively.
The PCM uses the MAP sensor input to aid in cal-
culating the following:
²Manifold pressure
²Barometric pressure
Fig. 20 5.7L IAT SENSOR R/I
1 - FRONT OF INTAKE MANIFOLD PLENUM
2 - IAT SENSOR
3 - RELEASE TAB
14 - 32 FUEL INJECTION - GASDR
INTAKE AIR TEMPERATURE SENSOR (Continued)

INTAKE AIR HEATER
DESCRIPTION
The intake manifold air heater element assembly
is located in the top of the intake manifold.
OPERATION
The air heater elements are used to heat incoming
air to the intake manifold. This is done to help
engine starting and improve driveability with cool or
cold outside temperatures.
Electrical supply for the 2 air heater elements is
controlled by the Engine Control Module (ECM)
through the 2 air heater relays. Refer to Intake Man-
ifold Air Heater Relays for more information.
Two heavy-duty cables connect the 2 air heater ele-
ments to the 2 air heater relays. Each of these cables
will supply approximately 95 amps at 12 volts to an
individual heating element within the heater block
assembly.
Refer to the Powertrain Diagnostic Procedures
manual for electrical operation and complete descrip-
tion of the intake heaters, including pre-heat and
post-heat cycles.
REMOVAL
If servicing either of the heater elements, the
entire block/element assembly must be replaced.
(1) Disconnect both negative battery cables at both
batteries. Cover and isolate ends of both cables.
(2) Remove both the intake manifold air intake
tube (above injection pump), and its rubber connector
hose (Fig. 26).
(3) Lift 2 rubber covers (Fig. 27) to gain access to 2
positive (+) cable nuts. Remove these 2 nuts (Fig. 28)
and remove 2 cables from studs.
(4) Disconnect ground strap (Fig. 27) at heater ele-
ment stud.
(5) Remove wiring harness clips.
(6) Remove engine oil dipstick tube bracket from
air inlet connection and fuel filter housing.
(7) Remove 4 housing mounting bolts (Fig. 27) and
remove heater element assembly.
INSTALLATION
If servicing either of the heater elements, the
entire block/element assembly must be replaced.
(1) Using 2 new gaskets, position element assem-
bly and air housing to intake manifold.
(2) Install ground cable to air housing.
(3) Install 4 housing bolts and tighten to 24 N´m
(18 ft. lbs.) torque.
(4) Connect 2 positive (+) heater cables at cable
mounting studs.Do not allow either of the cable
eyelets to contact any other metal source other
than the cable nuts/studs.
Fig. 24 INLET/PRESSURE SENSOR REMOVAL/
INSTALLATION
1 - INLET/PRESSURE SENSOR
2 - ELEC. CONNECTOR
3 - SENSOR MOUNTING SCREWS (2)
4 - TOP OF AIR FILTER COVER
Fig. 25 SENSOR O-RING
1 - IAT/PRESSURE SENSOR
2 - O-RING
14 - 80 FUEL INJECTION - DIESELDR
INLET AIR TEMPERATURE SENSOR/PRESSURE SENSOR (Continued)