1994 JEEP CHEROKEE service

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

found, refer to the DRB scan tool and the appropri-
ate Powertrain Diagnostics Procedures service
manual.
RELAYSÐOPERATION/TESTING
OPERATION
The following operations/tests apply to these
relays only:automatic shut down (ASD), fuel pump
and torque converter clutch. For operations/tests on
all other relays, refer to the appropriate section of
this service manual.
The relay terminal numbers from (Fig. 44) can be
found on the bottom of the relay:
²Terminal number 30 is connected to battery volt-
age and can be switched or B+ (hot) at all times.
²Terminal number 87A is connected (a circuit is
formed) to terminal 30 in the de-energized (normally
OFF) position.
²Terminal number 87 is connected (a circuit is
formed) to terminal 30 in the energized (ON) posi-
tion. Terminal number 87 then supplies battery volt-
age to the component being operated.
²Terminal number 86 is connected to a switched (+)
power source.
²Terminal number 85 is grounded by the power-
train control module (PCM).
TESTING
(1) Remove relay before testing.
(2) Using an ohmmeter, perform a resistance test
between terminals 85 and 86. Resistance value
(ohms) should be 7565 ohms for resistor equipped
relays.
(3) Connect the ohmmeter between terminals num-
ber 87A and 30. Continuity should be present at this
time.
(4) Connect the ohmmeter between terminals num-
ber 87 and 30. Continuity should not be present at
this time.
(5) Use a set of jumper wires (16 gauge or small-
er). Connect one jumper wire between terminal num-
ber 85 (on the relay) to the ground side (-) of a 12
Volt power source.
(6) Attach the other jumper wire to the positive
side (+) of a 12V power source. Do not connect the
jumper wire to relay at this time.
CAUTION: DO NOT ALLOW THE OHMMETER TO
CONTACT TERMINALS 85 OR 86 DURING THESE
TESTS. DAMAGE TO OHMMETER MAY RESULT.
(7) Attach the other jumper wire (12V +) to termi-
nal number 86. This will activate the relay. Continu-
ity should now be present between terminals number
Fig. 44 Relay Terminals
JFUEL SYSTEM 14 - 47

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

DRB SCAN TOOL
For operation of the DRB scan tool, refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual.
DIAGNOSTIC TROUBLE CODE (DTC)
On the following pages, a list of diagnostic trouble
codes is provided for the 2.5L 4 cylinder and 4.0L 6
cylinder engines. A DTC indicates that the power-
train control module (PCM) has recognized an abnor-
mal signal in a circuit or the system. A DTC may
indicate the result of a failure, but never identify the
failed component directly.
DIAGNOSTIC TROUBLE CODE DESCRIPTIONS
Diagnostic
Trouble
CodeDRB Scan Tool
DisplayDescription of Diagnostic Trouble Code
11* .......... NoCrank Reference
Signal at PCMNo crank reference signal detected during engine cranking.
12* ..........Battery Disconnect Direct battery input to PCM was disconnected within the last 50 Key-on
cycles.
13**.......... NoChange in MAP From
Start to RunNo difference recognized between the engine MAP reading and the
barometric (atmospheric) pressure reading at start-up.
14**.......... MAPSensor Voltage Too
LowMAP sensor input below minimum acceptable voltage.
or
MAP Sensor Voltage Too
HighMAP sensor input above maximum acceptable voltage.
15**.......... NoVehicle Speed Sensor
SignalNo vehicle distance (speed) sensor signal detected during road load
conditions.
17* ..........Engine is Cold Too Long Engine coolant temperature remains below normal operating temperatures
during vehicle travel (thermostat).
21**.......... O2SStays at Center Neither rich or lean condition detected from the oxygen sensor input.
or
O2S Shorted to Voltage Oxygen sensor input voltage maintained above the normal operating range.
22**.......... ECTSensor Voltage Too
HighEngine coolant temperature sensor input above maximum acceptable
voltage.
or
ECT Sensor Voltage Too
LowEngine coolant temperature sensor input below minimum acceptable voltage.
* Check Engine Lamp will not illuminate at all times if this Diagnostic Trouble Code was recorded. Cycle Ignition key as
described in manual and observe code flashed by Check Engine lamp.
** Check Engine Lamp will illuminate during engine operation if this Diagnostic Trouble Code was recorded.
Fig. 47 Data Link Connector Schematic
JFUEL SYSTEM 14 - 51

(3) Lower the vehicle.
PARK NEUTRAL SWITCH
Refer to Group 21, Transmissions for park neutral
switch service.
POWER STEERING PRESSURE SWITCHÐ2.5L
ENGINE ONLY
The power steering pressure switch is installed in
the power steering high pressure hose (Figs. 11 or
12).
REMOVAL
(1) Disconnect the electrical connector from the
power steering pressure switch.
(2) Place a small container or shop towel beneath
the switch to collect any excess fluid.
(3) Remove the switch.
INSTALLATION
(1) Install the power steering switch.
(2) Connect the electrical connector to the switch.(3) Check power steering fluid and add as neces-
sary.
(4) Start the engine and again check power steer-
ing fluid. Add fluid if necessary.
POWERTRAIN CONTROL MODULE (PCM)
On XJ models, the PCM is located in the engine
compartment next to the air cleaner (Fig. 13). On YJ
models, the PCM is located in the engine compart-
ment behind the windshield washer fluid reservoir
(Fig. 14).
REMOVAL
(1) Disconnect the negative battery cable at the
battery.
(2) YJ Models Only: Remove the windshield
washer fluid tank.
(3) Loosen the 60-Way connector mounting bolt
(Figs. 13 or 14).
(4) Remove the electrical connector by pulling
straight back.
(5) Remove the three PCM mounting bolts.
(6) Remove PCM.
Fig. 11 Power Steering Pressure SwitchÐYJ Models
Fig. 12 Power Steering Pressure SwitchÐXJ Models
Fig. 13 PCM LocationÐXJ Models
Fig. 14 PCM LocationÐYJ Models
14 - 58 FUEL SYSTEMJ

PROPELLER SHAFTS
CONTENTS
page page
GENERAL INFORMATION.................. 1
PROPELLER SHAFT REPLACEMENT......... 7
SERVICE DIAGNOSIS/PROCEDURES......... 3TORQUE SPECIFICATIONS................ 14
UNIVERSAL JOINT REPLACEMENT.......... 9
GENERAL INFORMATION
PROPELLER SHAFTS
The function of a propeller shaft is to transmit
power from one point to another. The shaft is de-
signed to send torque from the transmission (transfer
case on 4WD vehicles) to the axle (Fig. 1,2).The propeller shaft must operate through con-
stantly changing relative angles between the trans-
mission and axle. It must also be capable of changing
length while transmitting torque. The axle rides sus-
pended by springs in a floating motion. The prop-
Fig. 1 Propeller Shafts (XJ Vehicles)
Fig. 2 Propeller Shafts (YJ Vehicles)
JPROPELLER SHAFTS 16 - 1

shaft must be able to change operating angles when
going over various road surfaces. This is done
through universal joints, which permit the propeller
shaft to operate at different angles. The slip joints (or
yokes) permit contraction or expansion (Fig. 1,2).
Tubular propeller shafts are balanced by the man-
ufacturer with weights spot welded to the tube.
The propeller shaft is designed and built with the
yoke lugs in line with each other which is called
phasing. This design produces the smoothest running
condition, an out of phase shaft can cause a vibra-
tion.
Before undercoating a vehicle, the propeller
shaft and the U-joints should be covered. This
will prevent the undercoating from causing an
unbalanced condition and vibration.
CAUTION: Use exact replacement hardware for at-
taching the propeller shafts. The specified torque
must always be applied when tightening the fasten-
ers.
UNIVERSAL JOINTS
Two different types of U-joints are used with the
propeller shafts:
²Single cardan U-joint (Fig. 3)
²Double cardan U-joint (Fig. 4)
LUBRICATION
The slip yoke and certain universal joints are
equipped with zerk type lubrication fittings. They
should be lubricated with a multi-purpose NLGI
Grade 2 EP lubricant. All U-joints should be in-
spected for leakage and damage each time the vehi-
cle is serviced. If seal leakage or damage exists, the
U-joint should be replaced.
Fig. 3 Single Cardan Universal Joint
Fig. 4 Double Cardan (CV) Universal Joint
16 - 2 PROPELLER SHAFTSJ