Jeep Cherokee (XJ): Diagnosis and testing

Visual inspection

A visual inspection for loose, disconnected or incorrectly routed wires and hoses should be made. This should be done before attempting to diagnose or service the fuel injection system. A visual check will help spot these faults and save unnecessary test and diagnostic time. A thorough visual inspection will include the following checks: (1) Verify the three 32-way electrical connectors are fully inserted into the connector of the Powertrain Control Module (PCM) (Fig. 3).

Fig. 3 Powertrain Control Module (PCM)

1 - (3) 32-WAY CONNECTORS
2 - PCM

(2) Inspect battery cable connections. Be sure they are clean and tight.

(3) Inspect fuel pump relay and air conditioning compressor clutch relay (if equipped). Inspect ASD relay connections. Inspect starter motor relay connections.

Inspect relays for signs of physical damage and corrosion. The relays are located in Power Distribution Center (PDC) (Fig. 4). Refer to label on PDC cover for relay location.

(4) 2.5L Engine: Inspect ignition coil primary connection.

Verify coil secondary cable is firmly connected to coil (Fig. 5).

(5) 4.0L Engine: Inspect ignition coil connection (Fig. 6).

Fig. 4 Power Distribution Center (PDC)

1 - POWER DISTRIBUTION CENTER (PDC)

Fig. 5 Ignition Coil-2.5L Engine

1 - IGNITION COIL
2 - ELECTRICAL CONNECTOR
3 - MOUNTING BOLTS
4 - SECONDARY CABLE

(6) 2.5L Engine: Verify that distributor cap is correctly attached to distributor. Be sure that spark plug cables are firmly connected to the distributor cap and spark plugs are in their correct firing order.

Be sure that coil cable is firmly connected to distributor cap and coil.

Fig. 6 Ignition Coil-4.0L Engine

1 - REAR OF VALVE COVER
2 - COIL RAIL
3 - SLIDE TAB
4 - RELEASE LOCK
5 - COIL CONNECTOR

(7) Connect vehicle to an oscilloscope and inspect spark events for fouled or damaged spark plugs or cables.

(8) Verify generator output wire, generator connector and ground wire are firmly connected to generator.

(9) Inspect system body grounds for loose or dirty connections. Refer to Group 8, Wiring for ground locations.

(10) Verify crankcase ventilation (CCV) operation.

Refer to Group 25, Emission Control System for additional information.

(11) Inspect fuel tube quick-connect fitting-to-fuel rail connections.

(12) Verify hose connections to all ports of vacuum fittings on intake manifold are tight and not leaking.

(13) Inspect accelerator cable, transmission throttle cable (if equipped) and cruise control cable connections (if equipped). Check their connections to throttle arm of throttle body for any binding or restrictions.

(14) If equipped with vacuum brake booster, verify vacuum booster hose is firmly connected to fitting on intake manifold. Also check connection to brake vacuum booster.

(15) Inspect air cleaner inlet and air cleaner element for dirt or restrictions.

(16) Inspect radiator grille area, radiator fins and air conditioning condenser for restrictions.

(17) Verify intake manifold air temperature sensor wire connector is firmly connected to harness connector (Fig. 7) or (Fig. 8).

Fig. 7 Intake Manifold Air Temp. Sensor Location- 2.5L Engine

1 - ELECTRICAL CONNECTOR
2 - INTAKE MANIFOLD TEMPERATURE SENSOR
3 - FUEL INJECTOR

(18) Verify MAP sensor electrical connector is firmly connected to MAP sensor (Fig. 8). Also verify rubber L-shaped fitting from MAP sensor to throttle body is firmly connected (Fig. 9).

(19) Verify fuel injector wire harness connectors are firmly connected to injectors in correct order.

Each harness connector is numerically tagged with injector number (INJ 1, INJ 2 etc.) of its corresponding fuel injector and cylinder number.

(20) Verify harness connectors are firmly connected to idle air control (IAC) motor and throttle position sensor (TPS) (Fig. 8).

(21) Verify wire harness connector is firmly connected to engine coolant temperature sensor (Fig.

10).

(22) Raise and support vehicle.

Fig. 8 Sensor Locations-4.0L Engine

1 - MOUNTING BOLTS (4)
2 - THROTTLE BODY
3 - IAC MOTOR
4 - ELEC. CONN.
5 - TPS
6 - MAP SENSOR
7 - ELEC. CONN.
8 - IAT SENSOR
9 - ELEC. CONN.

Fig. 9 Rubber L-Shaped Fitting-MAP Sensor-to-Throttle Body

1 - THROTTLE BODY
2 - MAP SENSOR
3 - RUBBER FITTING
4 - MOUNTING SCREWS (2)

Fig. 10 Engine Coolant Temperature Sensor-Typical

1 - THERMOSTAT HOUSING
2 - ENGINE COOLANT TEMPERATURE SENSOR
3 - ELECTRICAL CONNECTOR

(23) Verify that all oxygen sensor wire connectors are firmly connected to sensors. Inspect sensors and connectors for damage (Fig. 11), (Fig. 12), (Fig. 13) or (Fig. 14).

Fig. 11 Front Oxygen Sensor-4.0L-Federal Emissions

1 - 1/1 O2S

Fig. 12 Oxygen Sensors-4.0L-California Emissions

1 - 1/1 O2S
2 - 2/1 O2S
3 - 2/2 O2S
4 - 1/2 O2S

Fig. 13 Front Oxygen Sensor-2.5L-Federal Emissions

1 - 1/1 O2S

Fig. 14 Rear Oxygen Sensor-2.5L/4.0L-Federal Emissions

1 - 1/2 O2S

(24) Inspect for pinched or leaking fuel tubes.

Inspect for pinched, cracked or leaking fuel hoses.

(25) Inspect for exhaust system restrictions such as pinched exhaust pipes, collapsed muffler or plugged catalytic convertor.

(26) If equipped with automatic transmission, verify electrical harness is firmly connected to park/neutral switch. Refer to Automatic Transmission section of Group 21.

(27) Verify that electrical harness connector is firmly connected to the vehicle speed sensor (Fig. 15).

(28) 2.5L 4-Cylinder Engine Only: Verify good electrical connection at power steering pressure switch (Fig. 16). This switch is not used with 4.0L engines.

(29) Verify good electrical connections at fuel pump module connector at front of fuel tank (Fig. 17).

(30) Verify good EVAP canister vent line connection at front of fuel tank (Fig. 17).

(31) Verify good fuel supply line connection at front of fuel tank (Fig. 17).

(32) Inspect all fuel lines/hoses for cracks or leaks.

(33) Inspect transmission torque convertor housing (automatic transmission) or clutch housing (manual transmission) for damage to timing ring on drive plate/flywheel.

(34) Verify battery cable and solenoid feed wire connections to starter solenoid are tight and clean.

Inspect for chaffed wires or wires rubbing up against other components.

Fig. 15 Vehicle Speed Sensor-Typical-4WD Shown

1 - SENSOR ELECTRICAL CONNECTOR
2 - SLIDE TAB
3 - 4WD TRANSFER CASE EXTENSION
4 - VEHICLE SPEED SENSOR
5 - RELEASE LOCK

Fig. 16 Power Steering Pressure Switch-2.5L Engine

1 - POWER STEERING PRESSURE SWITCH
2 - ELECTRICAL CONNECTOR
3 - POWER STEERING PUMP

Fig. 17 Fuel Tank Connections at Front of Fuel Tank

1 - FUEL PUMP MODULE CONNECTOR
2 - LEFT-REAR SHOCK ABSORBER
3 - EVAP CANISTER VENT LINE CONNECTION
4 - FRONT OF FUEL TANK
5 - FUEL SUPPLY LINE CONNECTION

ASD and fuel pump relays

The following description of operation and tests apply only to the Automatic Shutdown (ASD) and fuel pump relays. The terminals on the bottom of each relay are numbered. Two different types of relays may be used, (Fig. 18) or (Fig. 19).

Fig. 18 ASD and Fuel Pump Relay Terminals-Type 1

Fig. 19 ASD and Fuel Pump Relay Terminals-Type 2

OPERATION

•  Terminal number 30 is connected to battery voltage. For both the ASD and fuel pump relays, terminal 30 is connected to battery voltage at all times.
•  The PCM grounds the coil side of the relay through terminal number 85.
•  Terminal number 86 supplies voltage to the coil side of the relay.
•  When the PCM de-energizes the ASD and fuel pump relays, terminal number 87A connects to terminal 30. This is the Off position. In the off position, voltage is not supplied to the rest of the circuit. Terminal 87A is the center terminal on the relay.
•  When the PCM energizes the ASD and fuel pump relays, terminal 87 connects to terminal 30. This is the On position. Terminal 87 supplies voltage to the rest of the circuit.

TESTING

The following procedure applies to the ASD and fuel pump relays.

(1) Remove relay from connector before testing.

(2) With the relay removed from the vehicle, use an ohmmeter to check the resistance between terminals 85 and 86. The resistance should be between 75 65 ohms.

(3) Connect the ohmmeter between terminals 30 and 87A. The ohmmeter should show continuity between terminals 30 and 87A.

(4) Connect the ohmmeter between terminals 87 and 30. The ohmmeter should not show continuity at this time.

(5) Connect one end of a jumper wire (16 gauge or smaller) to relay terminal 85. Connect the other end of the jumper wire to the ground side of a 12 volt power source.

(6) Connect one end of another jumper wire (16 gauge or smaller) to the power side of the 12 volt power source. Do not attach the other end of the jumper wire to the relay at this time.

WARNING: DO NOT ALLOW OHMMETER TO CONTACT TERMINALS 85 OR 86 DURING THIS TEST.

(7) Attach the other end of the jumper wire to relay terminal 86. This activates the relay. The ohmmeter should now show continuity between relay terminals 87 and 30. The ohmmeter should not show continuity between relay terminals 87A and 30.

(8) Disconnect jumper wires.

(9) Replace the relay if it did not pass the continuity and resistance tests. If the relay passed the tests, it operates properly. Check the remainder of the ASD and fuel pump relay circuits. Refer to the Wiring Diagrams.

Throttle body minimum air flow check procedure

The following test procedure has been developed to check throttle body calibrations for correct idle conditions.

The procedure should be used to diagnose the throttle body for conditions that may cause idle problems.

This procedure should be used only after normal diagnostic procedures have failed to produce results that indicate a throttle body related problem. Be sure to check for proper operation of the idle air control motor before performing this test.

A special fixed orifice tool (number 6714) (Fig. 20) must be used for the following test. This tool has a fixed internal diameter of 0.185".

Fig. 20 6714 Fixed Orifice Tool

(1) Start the engine and bring to operating temperature.

Be sure all accessories are off before performing this test.

(2) Shut off engine and remove air duct at throttle body.

(3) 2.5L 4-Cylinder Engine: Near front/top of valve cover, disconnect CCV tube at fixed orifice fitting (Fig. 21). Insert Special Tool 6714 into end of disconnected CCV tube (insert either end of tool into tube). Let tool and tube hang disconnected at side of engine.

(4) 4.0L 6-Cylinder Engine: Disconnect CCV tube (Fig. 22) at intake manifold fitting. Attach a short piece of rubber hose to special tool 6714 (insert rubber hose to either end of tool). Install rubber hose/ tool to intake manifold fitting. Let CCV tube hang disconnected at side of engine.

Fig. 21 Install Orifice Tool 2.5L 4-Cylinder Engine

1 - AIR INLET FITTING
2 - AIR FILTER COVER
3 - FIXED ORIFICE FITTING

(5) Connect DRB scan tool to 16-way data link connector. This connector is located at lower edge of instrument panel near steering column. Refer to appropriate Powertrain Diagnostic Procedures service manual for DRB operation.

(6) Start engine and allow to warm up.

(7) Using the DRB scan tool, scroll through menus as follows: select-Stand Alone DRB III, select the year 2000 Diagnostics, select-Engine, select-System Test, select-Minimum Air Flow.

(8) The DRB scan tool will count down to stabilize idle rpm and display minimum air flow idle rpm. The idle rpm should be between 500 and 900 rpm. If idle speed is outside these specifications, replace throttle body. Refer to Throttle Body Removal/Installation.

(9) Disconnect DRB scan tool from vehicle.

(10) Remove orifice tool and connect CCV tube to engine.

(11) Install air duct to throttle body.

Fig. 22 Install Orifice Tool 4.0L 6-Cylinder Engine

1 - AIR INLET FITTING
2 - FIXED ORIFICE FITTING
3 - AIR FILTER COVER