1994 JEEP WRANGLER manual transmission

Fig. 4 Manual Transmission Fill- & Drain-Hole
PlugsÐTypical
JLUBRICATION AND MAINTENANCE 0 - 23

²Signal ground
Powertrain Control Module (PCM) Outputs
²A/C clutch relay
²Idle air control (IAC) motor
²Auto shut down (ASD) relay
²Generator field
²Malfunction indicator lamp
²Fuel injectors
²Fuel pump relay
²Ignition coil
²SCI transmit (DRB scan tool connection)
²Shift indicator lamp (manual transmission only)
²Speed control vacuum solenoid
²Speed control vent solenoid
²Tachometer (on instrument panel, if equipped)
²Torque converter clutch relay (3-speed auto. trans.
only)
The PCM contains a voltage convertor. This con-
verts battery voltage to a regulated 8.0 volts. It is
used to power the crankshaft position sensor and
camshaft position sensor. The PCM also provides a
five (5) volt supply for the Manifold Absolute Pres-
sure (MAP) sensor and Throttle Position Sensor
(TPS).
AIR CONDITIONING (A/C) CONTROLSÐPCM INPUT
The A/C control system information applies to fac-
tory installed air conditioning units only.
A/C SELECT SIGNAL:When the A/C switch is
in the ON position and the A/C low pressure switch
is closed, an input signal is sent to the powertrain
control module (PCM). The signal informs the PCM
that the A/C has been selected. The PCM adjusts idle
speed to a pre-programmed rpm through the idle air
control (IAC) motor to compensate for increased en-
gine load.
A/C REQUEST SIGNAL:Once A/C has been se-
lected, the PCM receives the A/C request signal from
the evaporator switch. The input indicates that the
evaporator temperature is in the proper range for
A/C application. The PCM uses this input to cycle
the A/C compressor clutch (through the A/C relay). It
will also determine the correct engine idle speed
through the IAC motor position.
If the A/C low pressure switch opens (indicating a
low refrigerant level), the PCM will not receive an
A/C select signal. The PCM will then remove the
ground from the A/C relay. This will deactivate the
A/C compressor clutch.
If the evaporator switch opens, (indicating that
evaporator is not in proper temperature range), the
PCM will not receive the A/C request signal. The
PCM will then remove the ground from the A/C re-
lay, deactivating the A/C compressor clutch.
AUTOMATIC SHUT DOWN (ASD) SENSEÐPCM
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 power distribution center (PDC) in the
engine compartment (Figs. 3 or 4). It is used to con-
nect oxygen sensor heater element, ignition coil, gen-
erator field winding and fuel injectors to 12 volt +
power supply. Also refer to Automatic Shut Down
RelayÐPCM Output.
This input is used only to sense that the ASD relay
is energized. If the PCM does not see 12 volts at this
input when the ASD should be activated, it will set a
Diagnostic Trouble Code (DTC).
BATTERY VOLTAGEÐPCM INPUT
The battery voltage input provides power to the
powertrain control module (PCM). It also informs the
PCM what voltage level is supplied to the ignition
coil and fuel injectors.
If battery voltage is low, the PCM will increase in-
jector pulse width (period of time that the injector is
Fig. 3 Power Distribution CenterÐYJ Models
Fig. 4 Power Distribution CenterÐXJ Models
JFUEL SYSTEM 14 - 19

energized). This is done to compensate for the re-
duced flow through injector caused by the lowered
voltage.
BRAKE SWITCHÐPCM INPUT
When the brake light switch is activated, the pow-
ertrain control module (PCM) receives an input indi-
cating that the brakes are being applied. After
receiving this input, the PCM maintains idle speed
to a scheduled rpm through control of the idle air
control (IAC) motor. The brake switch input is also
used to operate the speed control system.
CAMSHAFT POSITION SENSORÐPCM INPUT
A sync signal is provided by the camshaft position
sensor located in the ignition distributor (Fig. 5). The
sync signal from this sensor works in conjunction
with the crankshaft position sensor to provide the
powertrain control module (PCM) with inputs. This
is done to establish and maintain correct injector fir-
ing order.
Refer to Camshaft Position Sensor in Group 8D, Ig-
nition System for more information.
DATA LINK CONNECTORÐPCM INPUT
The data link connector (diagnostic scan tool con-
nector) links the DRB scan tool with the powertrain
control module (PCM). The data link connector is lo-
cated in the engine compartment (Figs. 6 or 7). For
operation of the DRB scan tool, refer to the appropri-
ate Powertrain Diagnostic Procedures service man-
ual.
The data link connector uses two different pins on
the PCM. One is for Data Link Transmit and the
other is for Data Link Receive.
INTAKE AIR TEMPERATURE SENSORÐPCM INPUT
The intake manifold air temperature sensor is in-
stalled in the intake manifold with the sensor ele-
ment extending into the air stream (Figs. 8 or 9).
The sensor provides an input voltage to the power-
train control module (PCM) indicating intake mani-
fold air temperature. The input is used along with
inputs from other sensors to determine injector pulse
width. As the temperature of the air-fuel stream in
the manifold varies, the sensor resistance changes.
This results in a different input voltage to the PCM.
CRANKSHAFT POSITION SENSORÐPCM INPUT
This sensor is a Hall Effect device that detects
notches in the flywheel (manual transmission), or
flexplate (automatic transmission).
This sensor is used to indicate to the powertrain
control module (PCM) that a spark and or fuel injec-
tion event is to be required. The output from this
sensor, in conjunction with the camshaft position
sensor signal, is used to differentiate between fuel in-
jection and spark events. It is also used to synchro-
nize the fuel injectors with their respective cylinders.
Fig. 5 Camshaft Position Sensor
Fig. 6 Data Link ConnectorÐYJ ModelsÐTypical
Fig. 7 Data Link ConnectorÐXJ ModelsÐTypical
14 - 20 FUEL SYSTEMJ

ing the IAC motor pintle in and out of the air control
passage. The IAC motor is positioned when the igni-
tion key is turned to the On position.
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.
IGNITION COILÐPCM OUTPUT
System voltage is supplied to the ignition coil pos-
itive terminal. The powertrain control module (PCM)
operates the ignition coil.Base (initial) ignition
timing is not adjustable.The PCM adjusts ignition
timing to meet changing engine operating conditions.
The ignition coil is located near the ignition distrib-
utor (Fig. 22).
Refer to Group 8D, Ignition System for additional
information.
MALFUNCTION INDICATOR LAMPÐPCM OUTPUT
The Malfunction Indicator Lamp (formerly referred
to as the Check Engine Lamp) illuminates on the in-
strument 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.
RADIATOR FAN RELAYÐPCM OUTPUT
XJ MODELS ONLY
The electric radiator cooling fan used in XJ models
(equipped with 4.0L engine, heavy duty cooling
and/or air conditioning) is controlled by the power-
train control module (PCM) through radiator fan re-
lay. The relay is energized when coolant temperature
is above 103ÉC (217ÉF). It will then de-energize when
coolant temperature drops to 98ÉC (208ÉF). Refer to
Group 7, Cooling Systems for more information.
The relay is located in the power distribution cen-
ter (PDC) (Fig. 23).
The electric radiator cooling fan is not used on YJ
models.
SCI TRANSMITÐPCM OUTPUT
SCI Transmit is the serial data communication
transmit circuit for the DRB scan tool. The power-
train control module (PCM) transmits data to the
DRB through the SCI Transmit circuit.
SHIFT INDICATORÐPCM 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.
Fig. 23 PDCÐXJ Models
Fig. 22 Ignition CoilÐTypical
14 - 26 FUEL SYSTEMJ

²Intake manifold air temperature sensor input is
monitored
²Throttle position sensor (TPS) is monitored
²The auto shut down (ASD) relay is energized by
the PCM for approximately three seconds.
²The 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
²The O2S sensor heater element is energized
through the fuel pump relay. The O2S sensor input
is not used by the PCM to calibrate air-fuel ratio
during this mode of operation.
²The 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:
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Starter motor relay
²Camshaft 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:
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distributor)
²Park/Neutral Switch (Gear indicator signalÐauto.
trans. only)
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)Based on these inputs the following occurs:
²Voltage 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.
²The PCM adjusts engine idle speed through the
idle air control (IAC) motor and adjusts ignition tim-
ing.
²The 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.
²If the vehicle has a manual transmission, the up-
shift light is operated by the PCM.
²When engine has reached operating temperature,
the PCM will begin monitoring O2S sensor 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:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distributor)
²Battery voltage
²Park/Neutral Switch (gear indicator signalÐauto.
trans. only)
²Oxygen sensor
Based on these inputs, the following occurs:
²Voltage 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.
²The PCM monitors the O2S sensor 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.
²The PCM adjusts ignition timing by increasing
and decreasing spark advance.
²The 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.
The optional Extended Idle Switch is used to raise
the engine idle speed to approximately 1000 rpm.
This is when the shifter is in either the Park or Neu-
tral position. A rocker-type 2-wire switch (extended
idle switch) is mounted to the instrument panel. This
14 - 28 FUEL SYSTEMJ

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.
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:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distributor)
²Park/Neutral switch (gear indicator signalÐauto.
trans. only)
²Oxygen (O2S) sensor
Based on these inputs, the following occurs:
²Voltage 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.
²The PCM monitors the O2S sensor input and ad-
justs air-fuel ratio. It also adjusts engine idle speed
through the idle air control (IAC) motor.
²The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
²The 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.
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distributor)²Park/Neutral switch (gear indicator signalÐauto.
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.
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distributor)
During wide open throttle conditions, the following
occurs:
²Voltage 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.
²The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
²The 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. 25). Fuel
does not enter the intake manifold through the throt-
JFUEL SYSTEM 14 - 29

(29) Verify that fuel pump module wire connector
is firmly connected to harness connector.
(30) Inspect fuel hoses at fuel pump module for
cracks or leaks (Fig. 28).
(31) Inspect transmission torque convertor housing
(automatic transmission) or clutch housing (manual
transmission) for damage to timing ring on drive
plate/flywheel.
(32) Verify that battery cable and solenoid feed
wire connections to the starter solenoid are tight and
clean. Inspect for chaffed wires or wires rubbing up
against other components (Fig. 29).
POWERTRAIN CONTROL MODULE (PCM) 60-WAY
CONNECTOR
For PCM 60-way connector wiring schematics, re-
fer to Group 8W, Wiring Diagrams.
SYSTEM SCHEMATICS
Fuel system schematics for the 2.5L 4 cylinder and
4.0L 6 cylinder engines are shown in figures 30, 31,
32 and 33.
Fig. 28 Fuel Pump Module Connector and Fuel HosesÐTypical
Fig. 29 Starter Solenoid ConnectionsÐTypical
14 - 38 FUEL SYSTEMJ

the sensor will not rotate, install the sensor with the
throttle shaft on the other side of the socket tangs).
The TPS will be under slight tension when rotated.
(1) Install the TPS and retaining bolts.
(2) Connect TPS electrical connector to TPS.
(3) Manually operate the throttle (by hand) to
check for any TPS binding before starting the en-
gine.
TORQUE CONVERTER CLUTCH RELAY
On YJ models, the TCC relay is located in the en-
gine compartment. It is attached to the cowl panel
with one bolt (Fig. 20). On XJ models, the TCC relay
is located in the power distribution center (PDC)
(Fig. 21). For location of this relay within the PDC,
refer to label on PDC cover.
VEHICLE SPEED SENSOR
The vehicle speed sensor (Fig. 22) is located on the
extension housing of the transmission on 2WD mod-
els. It is located on the transfer case on 4WD models.
REMOVAL
(1) Raise and support vehicle.
(2) Disconnect the electrical connector from the
sensor.
(3) Remove the sensor mounting bolt (Fig. 23).
Fig. 18 TPS LocationÐ4.0L Engine
Fig. 19 Throttle Position SensorÐInstallation
Fig. 20 TCC Relay LocationÐYJ Models
Fig. 21 Power Distribution CenterÐXJ Models
Fig. 22 Vehicle Speed Sensor LocationÐTypical
14 - 60 FUEL SYSTEMJ