Engine Controls - Tests W/o Codes Plymouth Laser I

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in appropriate BASIC TESTING and G - TESTS W/ CODES articles. Use this article to diagnose driveability problems existing when a hard fault code is not present or vehicle is not equipped with self-diagnostic system.

Note. Some driveability problems may have been corrected by the manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component, system test or an adjustment.

Use intermittent test procedures to locate driveability problems that DO NOT occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present, but no problem was found during self-diagnostic testing.

Note. For specific testing procedures, see appropriate I - SYS/COMP TESTS article. For specifications, see appropriate SPECIFICATIONS article.

SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC TESTING and G - TESTS W/ CODES articles were performed before diagnosing a symptom. Symptoms available for diagnosis include

1. No Start or Hard Start
2. Rough Idle
3. Rough Idle or Stumble
4. Hesitation or Poor Acceleration
5. Poor Fuel Mileage

NO START OR HARD START

1. Check fuel injection system
2. Check fuel pump drive control system
3. Check power transistor
4. Check power to electronic control unit
5. Check control relay
6. Check fuel injectors
7. Ensure fuel pressure is correct
8. Check for vacuum leaks
9. Malfunctioning engine control unit
10. Check for open or short in wiring harness and/or poor connections

ROUGH IDLE

1. Check vehicle speed sensor
2. Ensure fuel pressure is correct
3. Check for vacuum leak
4. Malfunctioning electronic control unit
5. Check for open or short in wiring harness and/or poor connections

ROUGH IDLE OR STUMBLE

1. Check fuel injection system
2. Check intake air temperature sensor
3. Check coolant temperature sensor
4. Check barometric pressure sensor
5. Check ignition switch
6. Check idle position switch
7. Check throttle position sensor
8. Check TDC sensor and crank angle sensor
9. Check power steering oil pressure switch
10. Check A/C switch
11. Check inhibitor switch (A/T models)
12. Check motor position sensor (1.8L)
13. Check airflow sensor
14. Check oxygen sensor
15. Check stepper motor (2.0L)
16. Check fuel injectors
17. Check power transistor

HESITATION OR POOR ACCELERATION

1. Check fuel injection system
2. Check intake air temperature sensor
3. Check coolant temperature sensor
4. Check barometric pressure sensor
5. Check ignition switch
6. Check idle position switch
7. Check throttle position sensor
8. Check TDC sensor and crank angle sensor
9. Check power steering oil pressure switch
10. Check A/C switch
11. Check inhibitor switch (A/T models)
12. Check motor position sensor (1.8L)
13. Check airflow sensor
14. Check oxygen sensor
15. Check stepper motor (2.0L)
16. Check fuel injectors
17. Check power transistor
18. Check A/C power relay
19. Check fuel pump pressure
20. Check for vacuum leak
21. Malfunctioning electronic control unit
22. Check for open or short in wiring harness and/or poor connections

POOR FUEL MILEAGE

1. Check fuel injection system
2. Check intake air temperature sensor
3. Check coolant temperature sensor
4. Check barometric pressure sensor
5. Check ignition switch
6. Check idle position switch
7. Check throttle position sensor
8. Check TDC sensor and crank angle sensor
9. Check power steering oil pressure switch
10. Check A/C switch
11. Check inhibitor switch (A/T models)
12. Check motor position sensor (1.8L)
13. Check airflow sensor
14. Check oxygen sensor
15. Check stepper motor (2.0L)
16. Check fuel injectors
17. Check power transistor
18. Check fuel pressure

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to the computer setting a fault code (on some systems) which may help in diagnosis.

If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.

Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position, or negative battery cable is disconnected when monitoring circuit resistance. Status change in DVOM while performing test procedures will indicate area of fault.

TEST PROCEDURES

Intermittent Simulation

To reproduce the conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.