1994 JEEP WRANGLER engine oil

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

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

(4) Inspect ignition coil connections. Verify that
coil secondary cable is firmly connected to coil (Figs.
5or6).(5) Verify that distributor cap is correctly attached
to distributor. Be sure that spark plug cables are
firmly connected to the distributor cap and the spark
plugs in their correct firing order. Be sure that coil
cable is firmly connected to distributor cap and coil.
Be sure that camshaft position sensor wire connector
is firmly connected to harness connector (Figs. 7 or
8). Inspect spark plug condition. Refer to Group 8D,
Ignition System. Connect vehicle to an oscilloscope
and inspect spark events for fouled or damaged spark
plugs or cables.
(6) Verify that generator output wire, generator
connector and ground wire are firmly connected to
the generator (Fig. 9).
(7) Inspect the system ground connections at the
cylinder block behind the engine oil dipstick tube
(Fig. 10).
Fig. 4 PDCÐXJ Models
Fig. 5 Ignition CoilÐ2.5L Engine
Fig. 6 Ignition CoilÐ4.0L Engine
Fig. 7 Distributor and WiringÐ2.5L Engine
Fig. 8 Distributor and WiringÐ4.0L Engine
JFUEL SYSTEM 14 - 33

87 and 30. Continuity should not be present between
terminals number 87A and 30.
(8) Disconnect jumper wires from relay and 12
Volt power source.
If continuity or resistance tests did not pass, re-
place relay. If tests passed, refer to Group 8W, Wir-
ing Diagrams for additional circuit information. Also
refer to the appropriate Powertrain Diagnostic Proce-
dures manual for operation of the DRB scan tool.
STARTER MOTOR RELAY TEST
Refer to Group 8A, Battery/Starting/Charging/Sys-
tem Diagnostics, for starter motor relay testing.
INJECTOR TEST
Disconnect the injector wire connector from the in-
jector. Place an ohmmeter on the injector terminals.
Resistance reading should be approximately 14.5
ohms61.2 ohms at 20ÉC (68ÉF). Proceed to following
Injector Diagnosis chart.
FUEL SYSTEM PRESSURE TEST
Refer to the Fuel Delivery System section of this
group. See Fuel System Pressure Test.
ON-BOARD DIAGNOSTICS (OBD)
The Powertrain Control Module (PCM) has been
programmed to monitor many different circuits of the
fuel injection system. If a problem is sensed in a
monitored circuit often enough to indicate an actual
problem, a Diagnostic Trouble Code (DTC) is stored.
The DTC will be stored in the PCM memory for
eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a diagnostic trou-
ble code (DTC) to be entered into PCM memory. The
criteria may be a specific range of engine rpm, en-
gine temperature and/or input voltage to the PCM.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. This may happen because one
of the DTC criteria for the circuit has not been met.
Example: assume that one of the criteria for the
MAP sensor circuit is that the engine must be oper-
ating between 750 and 2000 rpm to be monitored for
a DTC. If the MAP sensor output circuit shorts to
ground when the engine rpm is above 2400 rpm, a 0
volt input will be seen by the PCM. A DTC will not
be entered into memory because the condition does
not occur within the specified rpm range.
A DTC indicates that the powertrain control mod-
ule (PCM) has recognized an abnormal signal in a
circuit or the system. A DTC may indicate the result
of a failure, but never identify the failed component
directly.There are several operating conditions that the
PCM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non-Monitored
Circuits in this section.
MONITORED CIRCUITS
The powertrain control module (PCM) can detect
certain problems in the fuel injection system.
Open or Shorted Circuit- The PCM can deter-
mine if sensor output (which is the input to PCM) is
within proper range. It also determines if the circuit
is open or shorted.
Output Device Current Flow- The PCM senses
whether the output devices are hooked up.
If there is a problem with the circuit, the PCM
senses whether the circuit is open, shorted to ground
(-), or shorted to (+) voltage.
Oxygen Sensor- The PCM can determine if the
oxygen sensor is switching between rich and lean.
This is, once the system has entered Closed Loop. Re-
fer to Open Loop/Closed Loop Modes Of Operation in
the Component Description/System Operation section
for an explanation of Closed (or Open) Loop opera-
tion.
NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A Diagnostic
Trouble Code (DTC) may not be displayed for these
conditions.
Fuel Pressure: Fuel pressure is controlled by the
vacuum assisted fuel pressure regulator. The PCM
cannot detect a clogged fuel pump inlet filter, clogged
in-line fuel filter, or a pinched fuel supply or return
line. However, these could result in a rich or lean
condition causing an oxygen sensor DTC to be stored
in the PCM.
Secondary Ignition Circuit: The PCM cannot
detect an inoperative ignition coil, fouled or worn
spark plugs, ignition cross firing, or open circuited
spark plug cables.
Engine Timing: The PCM cannot detect an incor-
rectly indexed timing chain, camshaft sprocket or
crankshaft sprocket. The PCM also cannot detect an
incorrectly indexed distributor. However, these could
result in a rich or lean condition causing an oxygen
sensor DTC to be stored in the PCM.
Cylinder Compression: The PCM cannot detect
uneven, low, or high engine cylinder compression.
Exhaust System: The PCM cannot detect a
plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions: The PCM cannot de-
termine if the fuel injector is clogged, or the wrong
injector is installed. However, these could result in a
rich or lean condition causing an oxygen sensor DTC
to be stored in the PCM.
14 - 48 FUEL SYSTEMJ

Excessive Oil Consumption: Although the PCM
monitors exhaust stream oxygen content through ox-
ygen sensor (closed loop), it cannot determine exces-
sive oil consumption.
Throttle Body Air Flow: The PCM cannot detect
a clogged or restricted air cleaner inlet or air filter
element.
Evaporative System: The PCM will not detect a
restricted, plugged or loaded EVAP canister.
Vacuum Assist: Leaks or restrictions in the vac-
uum circuits of vacuum assisted engine control sys-
tem devices are not monitored by the PCM. However,
a vacuum leak at the MAP sensor will be monitored
and a diagnostic trouble code (DTC) will be gener-
ated by the PCM.
Powertrain Control Module (PCM) System
Ground: The PCM cannot determine a poor system
ground. However, a DTC may be generated as a re-
sult of this condition.
Powertrain Control Module (PCM) Connector
Engagement: The PCM cannot determine spread or
damaged connector pins. However, a DTC may be
generated as a result of this condition.
HIGH AND LOW LIMITS
The powertrain control module (PCM) compares in-
put signal voltages from each input device. It will es-
tablish high and low limits that are programmed into
it for that device. If the input voltage is not within
specifications and other Diagnostic Trouble Code
(DTC) criteria are met, a DTC will be stored in mem-
ory. Other DTC criteria might include engine rpm
limits or input voltages from other sensors or
switches. The other inputs might have to be sensed
by the PCM when it senses a high or low input volt-
age from the control system device in question.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be dis-
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the Malfunction
Indicator Lamp. This lamp was formerly referred to
as the Check Engine Lamp. The lamp is located on
the instrument panel.
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
scan tool connects to the data link connector in the
engine compartment (Figs. 45 or 46). For operation of
the DRB, refer to the appropriate Powertrain Diag-
nostic Procedures service manual.
EXAMPLES:
²If the lamp flashes 4 times, pauses and flashes 1
more time, a flashing Diagnostic Trouble Code (DTC)
number 41 is indicated.
²If the lamp flashes 4 times, pauses and flashes 6
more times, a flashing Diagnostic Trouble Code
(DTC) number 46 is indicated.After any stored DTC information has been ob-
served, the display will end with a flashing DTC
number 55. This will indicate the end of all stored
information.
Refer to the Diagnostic Trouble Code (DTC) charts
for DTC identification.
If the problem is repaired or ceases to exist, the
Powertrain Control Module (PCM) cancels the DTC
after 51 engine starts.
Diagnostic Trouble Codes indicate the results of a
failure, but never identify the failed component di-
rectly.
The circuits of the data link connector are shown
in (Fig. 47).
ERASING TROUBLE CODES
After the problem has been repaired, use the DRB
scan tool to erase a Diagnostic Trouble Code (DTC).
Refer to the appropriate Powertrain Diagnostic Pro-
cedures service manual for operation of the DRB
scan tool.
Fig. 45 Data Link ConnectorÐYJ ModelsÐTypical
Fig. 46 Data Link ConnectorÐXJ ModelsÐTypical
14 - 50 FUEL SYSTEMJ

MULTI-PORT FUEL INJECTION (MFI)ÐCOMPONENT REMOVAL/INSTALLATION
INDEX
page page
Accelerator Pedal and Throttle Cable......... 54
Air Cleaner Housing...................... 54
Air Conditioning (A/C) Clutch Relay........... 54
Air Filter............................... 54
Automatic Shut Down (ASD) Relay........... 54
Brake Switch............................ 54
Camshaft Position Sensor.................. 54
Crankshaft Position Sensor................. 55
Engine Coolant Temperature Sensor.......... 55
Fuel Filter.............................. 55
Fuel Injector............................ 55
Fuel Pump Module....................... 56
Fuel Pump Relay........................ 56
Fuel Rail Assembly....................... 56
Fuel System Pressure Release Procedure...... 56
Fuel Tank Pressure Relief/Rollover Valve...... 56
Fuel Tanks............................. 56Fuel Tubes/Lines/Hoses and Clamps.......... 56
Idle Air Control (IAC) Motor................. 56
Ignition Coil............................. 57
Intake Air Temperature Sensor.............. 54
Intake Manifold.......................... 57
Manifold Absolute Pressure (MAP) Sensor..... 57
Oxygen (O2S) Sensor..................... 57
Park Neutral Switch....................... 58
Power Steering Pressure SwitchÐ2.5L
Engine Only........................... 58
Powertrain Control Module (PCM)............ 58
Quick-Connect Fittings..................... 59
Throttle Body............................ 59
Throttle Position Sensor (TPS).............. 59
Torque Converter Clutch Relay.............. 60
Vehicle Speed Sensor..................... 60
ACCELERATOR PEDAL AND THROTTLE CABLE
Refer to the Accelerator Pedal and Throttle Cable
section of this group for removal/installation proce-
dures.
AIR CONDITIONING (A/C) CLUTCH RELAY
The A/C clutch relay is located in the Power Dis-
tribution Center (PDC) (Figs. 1 or 2). For location of
this relay within the PDC, refer to label on PDC
cover.
AIR CLEANER HOUSING
Refer to Group 25, Emission Control System.
AIR FILTER
Refer to Group 25, Emission Control System.
AUTOMATIC SHUT DOWN (ASD) RELAY
The ASD relay is located in the Power Distribution
Center (Figs. 1 or 2) (PDC). For location of this relay
within the PDC, refer to label on PDC cover.
BRAKE SWITCH
Refer to Group 5, Brakes for removal/installation
procedures.
CAMSHAFT POSITION SENSOR
For removal/installation procedures, refer to Group
8D, Ignition System. See Camshaft Position Sensor.
INTAKE AIR TEMPERATURE SENSOR
The intake manifold air temperature sensor is in-
stalled into the intake manifold plenum (Figs. 3 or
4).
Fig. 1 PDCÐYJ Models
Fig. 2 PDCÐXJ Models
14 - 54 FUEL SYSTEMJ

REMOVAL
(1) Disconnect the electrical connector from the
IAC motor.
(2) Remove IAC motor torx head mounting bolts.
(3) Remove IAC motor.
INSTALLATION
(1) Install IAC motor into throttle body and
tighten retaining bolts.
(2) Connect electrical connector to IAC motor.
IGNITION COIL
Refer to Group 8D, Ignition Systems for removal/
installation procedures.
INTAKE MANIFOLD
Refer to Group 11, Exhaust System and Intake
Manifold for removal/installation procedures.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor is located on the dash panel near
the rear of the engine cylinder head (valve) cover
(Fig. 9).
REMOVAL
(1) Disconnect the MAP sensor electrical connector
(Fig. 9).
(2) Disconnect the MAP sensor vacuum supply
hose (Fig. 9).
(3) Remove the MAP sensor mounting bolts and
remove MAP sensor.
INSTALLATION
(1) Install MAP sensor to dash panel and secure
with mounting bolts.
(2) Install the MAP sensor vacuum supply hose.
(3) Connect the MAP sensor electrical connector.
OXYGEN (O2S) SENSOR
The O2S sensor is installed in the exhaust down
pipe just below the exhaust manifold flange (Fig. 10).
REMOVAL
WARNING: THE EXHAUST MANIFOLD BECOMES
VERY HOT DURING ENGINE OPERATION. ALLOW
ENGINE TO COOL BEFORE REMOVING OXYGEN
SENSOR.
(1) Raise and support the vehicle.
(2) Separate the electrical connectors.
(3) Remove the O2S sensor from the exhaust man-
ifold. Snap-On oxygen sensor wrench (number YA
8875) may be used for removal and installation.
INSTALLATION
Threads of new factory oxygen sensors are coated
with anti-seize compound to aid in removal.
(1) Install the O2S sensor into the exhaust mani-
fold and tighten to 30 Nzm (22 ft. lbs.) torque.
(2) Connect the O2S sensor wire connector to the
main harness.
Fig. 8 Idle Air Control
MotorÐRemoval/InstallationÐTypical
Fig. 9 MAP SensorÐTypical
Fig. 10 Oxygen SensorÐTypical
JFUEL SYSTEM 14 - 57

Fig. 17 Align Oil Pump Gear ShaftÐ4.0L Engine
Fig. 18 Distributor InstallationÐTypical
Fig. 19 Rotor Alignment
8D - 26 IGNITION SYSTEMSJ