ROUGH IDLE
Check spark plugs, spark advance, ignition system wires and connections, starter solenoid for internal shorting (except 2.5L), and trigger wheel pin. See BASIC TESTING article. See SYSTEM/COMP TESTS article regarding the following procedures.
- Check MAP sensor circuit and vacuum hose.
- Check injector harness connectors.
- Check coolant temperature sensor for shorted sensor or circuit.
- Check for proper idle control system operation.
- Check for shorted, open or misadjusted TPS.
- Check EGR valve operation.
- Check for shorts or opens in oxygen sensor circuit.
- Check PCV valve operation.
POOR FUEL MILEAGE
Verify ignition timing and spark advance are correct. See BASIC TESTING article. Check ECU for proper operation. See SYSTEM/COMP TESTS article.
ERRATIC TIMING ADVANCE
Check vacuum advance mechanism and centrifugal advance weights. See SYSTEM/COMP TESTS article.
TIMING NOT AFFECTED BY VACUUM
Check vacuum advance mechanism and adjusting screws. See SYSTEM/COMP TESTS article. Check pickup coil pivot for corrosion. See BASIC TESTING article.
NO SPARK AT PLUGS
Check for open, loose, or corroded ground wires in distributor, and check primary wiring circuits. See BASIC TESTING article. Check for defective ignition module, cracked distributor cap, defective rotor. See BASIC TESTING article.
CRANKS NORMALLY WITH SPARK AT PLUGS
Check vacuum and wiring connections. See SYSTEM/COMP TESTS article. Check fuel for water or alcohol and check fuel tank residual pressure valve. See SYSTEM/COMP TESTS article. Verify proper operation of fuel pump, relay and wiring. See BASIC TESTING article. Check for an open in coolant temperature sensor circuit. See SYSTEM/COMP TESTS article. If engine is warm, check for flooding. See BASIC TESTING article. On 4.0L with automatic transmission, check if crank position sensor and grommet have been updated. New sensor and grommet are available from manufacturer. If replacement of sensor and grommet fail to correct condition, check ECU. See SYSTEM/COMP TESTS article.
ENGINE BACKFIRES, FAILS TO START
Verify ignition timing is correct, check for moisture in distributor or faulty distributor cap and verify that ignition wires are connected in proper firing order. See BASIC TESTING article.
ENGINE CONTINUES TO RUN WITH KEY OFF
Check for defective starter motor solenoid. See SYSTEM/COMP TESTS article. Check for shorted diode in alternator warning light circuit. See SYSTEM/COMP TESTS article.
ENGINE STARTS, THEN DIES
Check choke vacuum kick setting and low carburetor fuel level on carbureted engines. See BASIC TESTING article. Check fast idle RPM speed, cam index and fuel pressure. See BASIC TESTING article. Inspect vacuum system for leaks. See SYSTEM/COMP TESTS article. On 4.0L with automatic transmission, check if crank position sensor and grommet have been updated. New sensor and grommet are available from manufacturer. If replacement of sensor and grommet fail to correct condition, check ECU. See SYSTEM/COMP TESTS article.
HARD STARTING
Check idle control, EGR valve and control circuits for proper operation. See SYSTEM/COMP TESTS article. Check for A/C ON signal at ECU and for overcharged A/C system. See SYSTEM/COMP TESTS article. Verify injector circuits and fuses for proper operation and check for restricted fuel lines. See BASIC TESTING article.
PING OR KNOCK ON ACCELERATION
Check for shorts or opens in knock sensor and barometric sensor circuits. See SYSTEM/COMP TESTS article. Check ignition timing. See BASIC TESTING article. Check coolant system, belts and fan for proper operation. See SYSTEM/COMP TESTS article.
INTERMITTENT SIMULATION
To reproduce the conditions which create an intermittent fault so that it may be identified during testing, some of the following methods may be used
- Applying light vibration to components.
- Heating a component.
- Wiggling or bending a wiring harness.
- Applying humidity to a component.
- Remove or apply a vacuum supply source.
Monitor circuit/component voltage or resistance while attempting to simulate intermittent. If vehicle is running, monitor for self-diagnostic codes. Use the results of these tests to identify a faulty component or an area which should be checked closely for the problem.