Fuel Delivery and Air Induction: Testing and 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:

Fig.1 Powertrain Control Module (PCM):

1. Verify that the three 32-way electrical connectors are fully inserted into connector of Powertrain Control Module (PCM) (Fig. 1).
2. Inspect battery cable connections. Be sure that they are clean and tight.

Fig.2 Power Distribution Center (PDC):

3. Inspect fuel pump relay and 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. 2). Refer to label on PDC cover for relay location.

Fig.3 Ignition Coil - 2.5L Engine:

4. 2.5L Engine: Inspect ignition coil primary connection. Verify coil secondary cable is firmly connected to coil (Fig. 3).

Fig.4 Ignition Coil - 4.0L Engine:

5. 4.0L Engine: Inspect ignition coil connection (Fig. 4).
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.
7. Connect vehicle to an oscilloscope and inspect spark events for fouled or damaged spark plugs or cables.
8. Verify that generator output wire, generator connector and ground wire are firmly connected to the generator.
9. Inspect system body grounds for loose or dirty connections.
10. Verify Crankcase Ventilation (CCV) operation. Refer to Emission Control System for additional information.
11. Inspect fuel tube quick-connect fitting-to-fuel rail connections.
12. Verify that hose connections to all ports of vacuum fittings on intake manifold are tight and not leaking.
13. Inspect accelerator cable and transmission throttle cable (if equipped). Check their connections to throttle arm of throttle body for any binding or restrictions.
14. If equipped with vacuum brake booster, verify that 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.

Fig.5 Intake Manifold Air Temp. Sensor Location - 2.5L Engine:

Fig.6 Sensor Location - 4.0L Engine:

17. Verify intake manifold air temperature sensor wire connector is firmly connected to harness connector (Fig. 5) or (Fig. 6).

Fig.7 Rubber L-Shaped Fitting - MAP Sensor-To-Throttle Body:

18. Verify MAP sensor electrical connector is firmly connected to MAP sensor (Fig. 6). Also verify rubber L-shaped fitting from MAP sensor to throttle body is firmly connected (Fig. 7).
19. Verify that fuel injector wire harness connectors are firmly connected to injectors in the 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. 6).

Fig.8 Engine:

21. Verify wire harness connector is firmly connected to engine coolant temperature sensor (Fig. 8).
22. Raise and support vehicle.

Fig.9 Oxygen Sensor - 4.0L - Federal Emissions:

Fig.10 Oxygen Sensors - 4.0L - California Emissions:

Fig.11 Front Oxygen Sensor - 2.5L - Federal Emissions:

Fig.12 Rear Oxygen Sensor - 2.5L - Federal Emissions:

23. Verify that all oxygen sensor wire connectors are firmly connected to sensors. Inspect sensors and connectors for damage (Fig. 9), (Fig. 10), (Fig. 11) or (Fig. 12).
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 that electrical harness is firmly connected to park/neutral switch. Refer to Automatic Transmission.

Fig.13 Vehicle Speed Sensor - Typical - 4WD Shown:

27. Verify that electrical harness connector is firmly connected to the vehicle speed sensor (Fig. 13).
28. Verify that fuel pump/gauge sender unit wire connector is firmly connected to harness connector.
29. Inspect fuel hoses at fuel pump/gauge sender unit for cracks or leaks.
30. Inspect transmission torque convertor housing (automatic transmission) or clutch housing (manual transmission) for damage to timing ring on drive plate/flywheel.
31. Verify that 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.