1995 JEEP YJ engine coolant

(9) If equipped, disconnect the power steering
pump bracket. Set the pump and bracket aside. DO
NOT disconnect the hoses.
(10) Perform the Fuel System Pressure Release
procedure (refer to Group 14, Fuel System).
(11) Remove the fuel lines and vacuum advance
hose.
(12) Remove the intake and engine exhaust mani-
folds from the engine cylinder head (refer to Group
11, Exhaust System and Intake Manifold for the
proper procedures).
(13) Disconnect the ignition wires and remove the
spark plugs.
(14) Disconnect the temperature sending unit wire
connector.
(15) Remove the ignition coil and bracket assem-
bly.
(16) Remove the engine cylinder head bolts. Bolt
No.14 cannot be removed until the head is moved for-
ward (Fig. 6). Pull bolt No.14 out as far as it will go
and then suspend the bolt in this position (tape
around the bolt).
(17) Remove the engine cylinder head and gasket
(Fig. 6).
(18) If this was the first time the bolts were re-
moved, put a paint dab on the top of the bolt. If the
bolts have a paint dab on the top of the bolt or it
isn't known if they were used before, discard the
bolts.
(19) Stuff clean lint free shop towels into the cylin-
der bores.
CLEANING
Thoroughly clean the engine cylinder head and cyl-
inder block mating surfaces. Clean the intake and
engine exhaust manifold and engine cylinder head
mating surfaces. Remove all gasket material and car-
bon.
Check to ensure that no coolant or foreign material
has fallen into the tappet bore area.Remove the carbon deposits from the combustion
chambers and top of the pistons.
INSPECTION
Use a straightedge and feeler gauge to check the
flatness of the engine cylinder head and block mating
surfaces.
INSTALLATION
The engine cylinder head gasket is a composition
gasket. The gasket is to be installed DRY.DO NOT
use a gasket sealing compound on the gasket.
If the engine cylinder head is to be replaced and
the original valves used, measure the valve stem di-
ameter. Only standard size valves can be used with a
service replacement engine cylinder head unless the
replacement head valve stem guide bores are reamed
to accommodate oversize valve stems. Remove all
carbon buildup and reface the valves.
(1) Remove the shop towels from the cylinder
bores. Coat the bores with clean engine oil.
(2) Position the engine cylinder head gasket (with
the numbers facing up) onto the cylinder block.
CAUTION: Engine cylinder head bolts should be re-
used only once. Replace the head bolts if they were
used before or if they have a paint dab on the top
of the bolt.
(3) With bolt No.14 held in place (tape around
bolt), install the engine cylinder head. Remove the
tape from bolt No.14.
(4) Coat the threads of stud bolt No.11 with Loctite
592 sealant, or equivalent.
(5) Tighten the engine cylinder head bolts in se-
quence according to the following procedure (Fig. 7):
(a) Tighten all bolts in sequence (1 through 14)
to 30 Nzm (22 ft. lbs.) torque.
(b) Tighten all bolts in sequence (1 through 14)
to 61 Nzm (45 ft. lbs.) torque.
(c) Check all bolts to verify they are set to 61
Nzm (45 ft. lbs.) torque.
(d) Tighten bolts (in sequence):
²Bolts 1 through 10 to 149 Nzm (110 ft. lbs.) torque.
²Bolt 11 to 13 Nzm (100 ft. lbs.) torque.
²Bolts 12 through 14 to 149 Nzm (110 ft. lbs.)
torque.
CAUTION: During the final tightening sequence,
bolt No.11 will be tightened to a lower torque than
the rest of the bolts. DO NOT overtighten bolt
No.11.
(e) Check all bolts in sequence to verify the cor-
rect torque.
(f) If not already done, clean and mark each bolt
with a dab of paint after tightening. Should you en-
Fig. 6 Engine Cylinder Head Assembly
9 - 68 4.0L ENGINEJ

counter bolts which were painted in an earlier ser-
vice operation, replace them.
(6) Install the ignition coil and bracket assembly.
(7) Connect the temperature sending unit wire
connector.
(8) Install the spark plugs and tighten to 37 Nzm
(27 ft. lbs.) torque. Connect the ignition wires.
(9) Install the intake and engine exhaust mani-
folds (refer to Group 11, Exhaust System and Intake
Manifold for the proper procedures).
(10) Install the fuel lines and the vacuum advance
hose.
(11) If equipped, attach the power steering pump
and bracket.
(12) Install the push rods, rocker arms, pivots and
bridges in the order they were removed (refer to
Rocker Arms and Push Rods in this section).
(13) Install the engine cylinder head cover.
(14) Attach the air conditioner compressor mount-
ing bracket to the engine cylinder head and block.
Tighten the bolts to 40 Nzm (30 ft. lbs.) torque.
(15) Attach the air conditioning compressor to the
bracket. Tighten the bolts to 27 Nzm (20 ft. lbs.)
torque.
CAUTION: The serpentine drive belt must be routed
correctly. Incorrect routing can cause the water
pump to turn in the opposite direction causing the
engine to overheat.
(16) Install the serpentine drive belt and correctly
tension the belt (refer to Group 7, Cooling System for
the proper procedure).
(17) Install the air cleaner and ducting.
(18) Install the engine cylinder head cover.
(19) Connect the hoses to the engine thermostat
housing and fill the cooling system to the specified
level (refer to Group 7, Cooling Systems for the
proper procedure).
(20) The automatic transmission throttle linkage
and cable must be adjusted after completing the en-
gine cylinder head installation (refer to Group 21,
Transmissions for the proper procedures).(21) Install the temperature sending unit and con-
nect the wire connector.
(22) Connect the fuel line.
(23) Connect negative cable to battery.
(24) Connect the upper radiator hose and heater
hose at the engine thermostat housing.
(25) Fill the cooling system. Check for leaks.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN DIRECT
LINE WITH THE FAN. DO NOT PUT HANDS NEAR
THE PULLEYS, BELTS OR FAN. DO NOT WEAR
LOOSE CLOTHING.
(26) Operate the engine with the radiator cap off.
Inspect for leaks and continue operating the engine
until the engine thermostat opens. Add coolant, if re-
quired.
VALVES AND VALVE SPRINGS
This procedure is done with the engine cylinder
head removed from the block.
REMOVAL
(1) Remove the engine cylinder head from the cyl-
inder block.
(2) Use Valve Spring Compressor Tool
MD-998772A and compress each valve spring.
(3) Remove the valve locks, retainers, springs and
valve stem oil seals. Discard the oil seals.
(4) Use an Arkansas smooth stone or a jewelers
file to remove any burrs on the top of the valve stem,
especially around the groove for the locks.
(5) Remove the valves, and place them in a rack in
the same order as removed.
VALVE CLEANING
Clean all carbon deposits from the combustion
chambers, valve ports, valve stems, valve stem
guides and head.
Clean all grime and gasket material from the en-
gine cylinder head machined gasket surface.
INSPECTION
Inspect for cracks in the combustion chambers and
valve ports.
Inspect for cracks on the exhaust seat.
Inspect for cracks in the gasket surface at each
coolant passage.
Inspect valves for burned, cracked or warped
heads.
Inspect for scuffed or bent valve stems.
Replace valves displaying any damage.
VALVE REFACING
(1) Use a valve refacing machine to reface the in-
take and exhaust valves to the specified angle.
Fig. 7 Engine Cylinder Head Bolt Tightening
Sequence
J4.0L ENGINE 9 - 69

properly aligned ensures correct valve timing. A worn
or stretched timing chain will adversely affect valve
timing. If the timing chain deflects more than 12.7
mm (1/2 inch) replace it. The correct timing chain
has 48 pins. A chain with more than 48 pins will
cause excessive slack.
INSTALLATION
Assemble the timing chain, crankshaft sprocket
and camshaft sprocket with the timing marks
aligned (Fig. 5).
(1) Apply Mopar Silicone Rubber Adhesive Sealant
to the keyway in the crankshaft and insert the key.
With the key in the keyway on the crankshaft, install
the assembly on the crankshaft and camshaft.
(2) Install the camshaft sprocket retaining preload
bolt and washer (Fig. 7). Tighten the preload bolt to
108 Nzm (80 ft. lbs.) torque.
(3) To verify correct installation of the timing
chain, turn the crankshaft to position the camshaft
sprocket timing mark as shown in Fig. 8. Count the
number of chain pins between the timing marks of
both sprockets. There must be 15 pins.
(4) Install the crankshaft oil slinger.
(5) Replace the oil seal in the timing case cover.
(6) Lubricate the tension spring, thrust pin and
pin bore in the preload bolt with Mopar Engine Oil
Supplement, or equivalent. Install the spring and
thrust pin in the preload bolt head (Fig. 6).
(7) Install the timing case cover and gasket.
(8) With the key installed in the crankshaft key-
way, install the vibration damper, washer and bolt.
Lubricate and tighten the bolt to 108 Nzm (80 ft. lbs.)
torque.
(9) Install the serpentine drive belt and tighten to
the specified tension (refer to Group 7, Cooling Sys-
tem for the proper procedure).
(10) Install the fan and hub (or Tempatrol fan) as-
sembly. Install the shroud.
(11) Connect negative cable to battery.
CAMSHAFT
REMOVAL
WARNING: THE COOLANT IN A RECENTLY OPER-
ATED ENGINE IS HOT AND PRESSURIZED. RE-
LEASE THE PRESSURE BEFORE REMOVING THE
DRAIN COCK, CAP AND DRAIN PLUGS.
(1) Disconnect negative cable from battery.
(2) Drain the cooling system. DO NOT waste reus-
able coolant. If the solution is clean, drain it into a
clean container for reuse.
(3) Remove the radiator or radiator and condenser,
if equipped with A/C (refer to Group 7, Cooling Sys-
tem for the proper procedure).
(4) Remove the air conditioner condenser and re-
ceiver/drier assembly as a charged unit, if equipped
(refer to Group 24, Heating and Air Conditioning).
(5) Remove the distributor cap and mark the posi-
tion of the rotor.
(6) Remove the distributor and ignition wires.
(7) Remove the engine cylinder head cover.
(8) Remove the rocker arms, bridges and pivots.
(9) Remove the push rods.
(10) Remove the engine cylinder head and gasket.
(11) Remove the hydraulic valve tappets from the
engine cylinder head.
(12) Remove the vibration damper.
(13) Remove the timing case cover.
(14) Remove the timing chain and sprockets.
(15) Remove the front bumper and/or grille, as re-
quired.
(16) Remove the camshaft (Fig. 8).
Fig. 6 Camshaft Sprocket Preload Bolt
Fig. 7 Verify SprocketÐChain InstallationÐTypical
9 - 74 4.0L ENGINEJ

INSPECTION
Inspect the cam lobes for wear.
Inspect the bearing journals for uneven wear pat-
tern or finish.
Inspect the bearings for wear.
Inspect the distributor drive gear for wear.
If the camshaft appears to have been rubbing
against the timing case cover, examine the oil pres-
sure relief holes in the rear cam journal. The oil
pressure relief holes must be free of debris.
INSTALLATION
(1) Lubricate the camshaft with Mopar Engine Oil
Supplement, or equivalent.
(2) Carefully install the camshaft to prevent dam-
age to the camshaft bearings (Fig. 8).
(3) Install the timing chain, crankshaft sprocket
and camshaft sprocket with the timing marks
aligned.
(4) Install the camshaft sprocket retaining preload
bolt. Tighten the bolt to 108 Nzm (80 ft. lbs.) torque.
(5) Lubricate the tension spring, the thrust pin
and the pin bore in the preload bolt with Mopar En-
gine Oil Supplement, or equivalent. Install the spring
and thrust pin in the preload bolt head.
(6) Install the timing case cover with a replace-
ment oil seal (Fig. 9). Refer to Timing Case Cover In-
stallation.
(7) Install the vibration damper (Fig. 9).
(8) Install the hydraulic valve tappets.
(9) Install the engine cylinder head.
(10) Install the push rods.
(11) Install the rocker arms and pivot and bridge
assemblies. Tighten each of the capscrews for each
bridge alternately, one turn at a time, to avoid dam-
aging the bridge.
(12) Install the engine cylinder head cover.
(13) Position the oil pump gear. Refer to Distribu-
tor in the Component Removal/Installation section of
Group 8D, Ignition Systems.(14) Install the distributor and ignition wires. Re-
fer to Distributor in the Component Removal/Instal-
lation section of Group 8D, Ignition Systems.
(13) Install the serpentine drive belt and tighten to
the specified tension (refer to Group 7, Cooling Sys-
tem for the proper procedure).
During installation, lubricate the hydraulic
valve tappets and all valve components with
Mopar Engine Oil Supplement, or equivalent.
The Mopar Engine Oil Supplement, or equiva-
lent must remain with the engine oil for at
least 1 609 km (1,000 miles). The oil supplement
need not be drained until the next scheduled
oil change.
(16) Install the A/C condenser and receiver/drier
assembly, if equipped (refer to Group 24, Heating and
Air Conditioning).
CAUTION: Both service valves must be opened be-
fore the air conditioning system is operated.
(17) Install the radiator, connect the hoses and fill
the cooling system to the specified level (refer to
Group 7, Cooling System for the proper procedure).
(18) Check the ignition timing and adjust as neces-
sary.
(19) Install the grille and bumper, if removed.
(20) Connect negative cable to battery.
CAMSHAFT PIN REPLACEMENT
REMOVAL
WARNING: DO NOT LOOSEN THE RADIATOR
DRAIN COCK WITH THE SYSTEM HOT AND PRES-
SURIZED BECAUSE SERIOUS BURNS FROM COOL-
ANT CAN OCCUR.
(1) Disconnect negative cable from battery.
(2) Drain the radiator. DO NOT waste reusable
coolant. Drain the coolant into a clean container.
Fig. 9 Timing Case Cover ComponentsFig. 8 Camshaft
J4.0L ENGINE 9 - 75

CAUTION: When disconnecting the cruise control
connector at the throttle body, DO NOT pry the con-
nector off with pliers or screwdriver. Use finger
pressure only. Prying the connector off could break
it.
(9) Disconnect the electrical connectors. Pull the
harnesses away from the manifold.
²The throttle position sensor.
²The idle speed control motor.
²The coolant temperature sensor at the thermostat.
²The manifold air temperature sensor at the intake
manifold.
²The fuel injectors.
²The oxygen sensor.
(10) Disconnect the crankcase ventilation (CCV)
vacuum hose and manifold absolute pressure (MAP)
sensor vacuum hose connector at the intake mani-
fold.
(11) Disconnect vacuum hose from vacuum port on
the intake manifold.
(12) Disconnect CCV hose at the cylinder head
cover (Fig. 12).
(13) Remove the molded vacuum harness.
(14) Disconnect the vacuum brake booster hose at
the intake manifold.
(15) Remove bolts 2 through 5 securing the intake
manifold to the cylinder head (Fig. 11). Slightly
loosen bolt No.1 and nuts 6 and 7.
(16) Remove the intake manifold and gaskets.
Drain the coolant from the manifold.
CLEANING
Clean the intake manifold and cylinder head mat-
ing surfaces.DO NOT allow foreign material to
enter either the intake manifold or the ports in
the cylinder head.
INSTALLATION
(1) Install the new intake manifold gasket over the
locating dowels.
(2) Position the manifold in place and finger
tighten the mounting bolts.
(3) Tighten the fasteners in sequence and to the
specified torque (Fig. 11).
²Fastener No.1ÐTighten to 41 Nzm (30 ft. lbs.)
torque.
²Fasteners Nos.2 through 7ÐTighten to 31 Nzm (23
ft. lbs.) torque.
(4) Connect the fuel return and supply tube to the
connector next to the fuel rail. Push them into the
fitting until a click is heard. Verify that the connec-
tions are complete.
²First, ensure only the retainer tabs protrude from
the connectors.
²Second, pull out on the fuel tubes to ensure they
are locked in place.
(5) Connect the molded vacuum hoses to the vac-
uum port on the intake manifold and the cylinder
head cover.
(6) Connect the electrical connectors.
²The throttle position sensor.
²The automatic idle speed control motor.
²The coolant temperature sensor at the thermostat
housing.
²The fuel injectors.
²The air manifold temperature sensor.
²The oxygen sensor.
(7) Connect the CCV vacuum hose and MAP sen-
sor vacuum hose connectors to the throttle body.
(8) Install the power steering pump and bracket
assembly to the water pump and intake manifold.
(9) Connect the accelerator cable and cruise control
cable to the holddown bracket and the throttle arm.
CAUTION: Ensure that the accessory drive belt is
routed correctly. Failure to do so can cause the wa-
ter pump to turn in the opposite direction resulting
in engine overheating. Refer to Group 7, Cooling
System for the proper procedure.
(10) Tension the accessory drive belt. Refer to
Group 7, Cooling System for the proper procedure.
(11) Connect the air inlet hose to the throttle body
and the air cleaner.
(12) Connect the battery negative cable.
(13) Start the engine and check for leaks.
INTAKE MANIFOLDÐ4.0L ENGINE
The intake and engine exhaust manifolds on the
4.0L engine must be removed and installed together.
The two manifolds use a common gasket at the cyl-
inder head.
REMOVAL
(1) Disconnect the battery negative cable.
Fig. 12 Crankcase Ventilation (CCV) Hose (2.5L
Engine)
11 - 8 EXHAUST SYSTEM AND INTAKE MANIFOLDJ

MULTI-PORT FUEL INJECTION (MFI)ÐCOMPONENT DESCRIPTION/SYSTEM
OPERATION
INDEX
page page
Air Cleaner.............................. 29
Air Conditioning (A/C) Clutch RelayÐPCM Output . 26
Air Conditioning (A/C) ControlsÐPCM Input...... 21
Auto Shutdown (ASD) RelayÐPCM Output...... 26
Automatic Shutdown (ASD) SenseÐPCM Input . . . 21
Battery VoltageÐPCM Input................. 21
Brake SwitchÐPCM Input................... 22
Camshaft Position SensorÐPCM Input......... 22
Crankshaft Position SensorÐPCM Input........ 22
Data Link ConnectorÐPCM Input............. 22
Data Link ConnectorÐPCM Output............ 27
EMR LampÐPCM Output................... 27
Engine Coolant Temperature SensorÐPCM Input . 23
Extended Idle SwitchÐPCM Input............. 23
Fuel InjectorsÐPCM Output................. 27
Fuel Pressure Regulator.................... 33
Fuel Pump RelayÐPCM Output.............. 27
Fuel Rail................................ 33
General Information....................... 19
Generator FieldÐPCM Output................ 27
Generator LampÐPCM Output............... 27
Idle Air Control (IAC) MotorÐPCM Output....... 27
Ignition Circuit SenseÐPCM Input............. 23
Ignition CoilÐPCM Output................... 28Intake Manifold Air Temperature SensorÐ
PCM Input............................. 22
Malfunction Indicator LampÐPCM Output....... 28
Manifold Absolute Pressure (MAP) SensorÐPCM
Input................................. 23
Open Loop/Closed Loop Modes of Operation..... 30
Oxygen (O2S) SensorÐPCM Input............ 24
Park/Neutral SwitchÐPCM Input.............. 24
Power Ground........................... 24
Power Steering Pressure SwitchÐPCM Input.... 24
Powertrain Control Module (PCM)............. 20
Radiator Fan RelayÐPCM Output............. 28
SCI ReceiveÐPCM Input................... 24
SCI TransmitÐPCM Output.................. 29
Sensor ReturnÐPCM Input.................. 25
Shift IndicatorÐPCM Output................. 29
Speed ControlÐPCM Input.................. 25
Speed ControlÐPCM Output................. 29
TachometerÐPCM Output................... 29
Throttle Body............................ 33
Throttle Position Sensor (TPS)ÐPCM Input...... 25
Torque Converter Clutch RelayÐPCM Output.... 29
Vehicle Speed SensorÐPCM Input............ 25
GENERAL INFORMATION
All 2.5L 4-cylinder and 4.0L 6-cylinder engines are
equipped with sequential Multi-Port Fuel Injection
(MFI). The MFI system provides precise air/fuel ra-
tios 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 con-
trol devices, charging system, speed control, air con-
ditioning compressor clutch engagement and idle
speed. The PCM can adapt its programming to meet
changing operating conditions.
Powertrain Control Module (PCM) Inputsrep-
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 inprecise 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
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:
²Exhaust gas oxygen content
²Engine coolant temperature
²Manifold absolute pressure (MAP)
²Engine speed
²Throttle position
²Battery voltage
²Air conditioning selection
²Transmission gear selection (automatic transmis-
sions only)
²Speed 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 position. The PCM
JFUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION 14 - 19

provides a ground for the ignition coil. The coil dis-
charges when the PCM supplies a ground. By switch-
ing the ground path on and off, the PCM regulates
ignition timing.
The sensors and switches that provide inputs to
the powertrain control module (PCM) comprise the
Engine Control System. It is also comprised of the
PCM Outputs (engine control devices that the are op-
erated 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 MFI SystemÐGeneral
Diagnosis section of this group for DTC information.
POWERTRAIN CONTROL MODULE (PCM)
The PCM operates the fuel system. The PCM was
formerly referred to as the SBEC or engine control-
ler. The PCM is a pre-programmed, dual microproces-
sor digital computer. It regulates ignition timing, air-
fuel ratio, emission control devices, charging system,
speed control, air conditioning compressor clutch en-
gagement and idle speed. The PCM can adapt its
programming to meet changing operating conditions.
On XJ models, the PCM is located in the engine
compartment next to the air cleaner (Fig. 1). On YJ
models, the PCM is located in the engine compart-
ment behind the windshield washer fluid reservoir
(Fig. 2).
The PCM receives input signals from various
switches and sensors. Based on these inputs, the
PCM regulates various engine and vehicle operations
through different system components. These compo-
nents are referred to as PCM Outputs. The sensors
and switches that provide inputs to the PCM are con-
sidered PCM Inputs.The PCM adjusts ignition timing based upon in-
puts it receives from sensors that react to: engine
rpm, manifold absolute pressure, coolant tempera-
ture, throttle position, transmission gear selection
(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, 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:
²Generator output
²A/C request (if equipped with factory A/C)
²A/C select (if equipped with factory A/C)
²Auto shutdown (ASD) sense
²Intake manifold air temperature sensor
²Battery voltage
²Brake switch
²Engine coolant temperature sensor
²Crankshaft position sensor
²Ignition circuit sense (ignition switch in run posi-
tion)
²Manifold absolute pressure sensor
²Overdrive/override switch
²Oxygen sensor
²Park/neutral switch (auto. trans. only)
²SCI receive (DRB scan tool connection)
²Speed control resume switch
²Speed control set switch
²Speed control on/off switch
²Camshaft position sensor signal
²Throttle position sensor
²Vehicle speed sensor
²Sensor return
²Power ground
Fig. 1 PCM LocationÐXJ Models
Fig. 2 PCM LocationÐYJ Models
14 - 20 FUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATIONJ

The engine will not operate if the PCM does not re-
ceive a crankshaft position sensor input.
ENGINE COOLANT TEMPERATURE SENSORÐPCM
INPUT
The engine coolant temperature sensor is installed
in the thermostat housing (Fig. 10) 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's
resistance changes. The 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.
Refer to Open Loop/Closed Loop Modes of Opera-
tion in this section of the group for more information.
EXTENDED IDLE SWITCHÐPCM INPUT
OPTIONAL POLICE PACKAGE ONLY
The extended idle switch is used to raise the en-
gine idle speed to approximately 1000 rpm. This is
when the shifter is in either the Park or Neutral po-
sition. A rocker-type 2-wire switch (extended idle
switch) is mounted to the instrument panel. This
switch will supply a ground circuit to the powertrain
control module (PCM).The switch is available
only with 4.0L engine when supplied with the
optional police package.
For testing and diagnosis of this switch and its cir-
cuit, refer to the MFI SystemÐGeneral Diagnosis
section of this group.
IGNITION CIRCUIT SENSEÐPCM INPUT
The ignition circuit sense input tells the powertrain
control module (PCM) the ignition switch has ener-
gized the ignition circuit. Refer to the wiring dia-
grams for circuit information.
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSORÐPCM 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.
Fig. 8 Sensor LocationÐ4.0L Engine
Fig. 9 Sensor LocationÐ2.5L Engine
Fig. 10 Engine Coolant Temperature SensorÐ
Typical
JFUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION 14 - 23