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Engine Controls - Tests W/o Codes Mercury Capri III

Testing & Diagnostics ~839 words

INTRODUCTION

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

Note. Some driveability problems may have been corrected by 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 adjustment.

Use intermittent test procedures to locate driveability problems which 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 SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE Section. For specifications, see ADJUSTMENTS or SPECIFICATIONS article in the ENGINE PERFORMANCE Section.

SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC TESTING and TESTS W/CODES articles in the ENGINE PERFORMANCE Section were performed before diagnosing a symptom. These symptoms are available for diagnosis.

  1. Backfire through induction or exhaust.
  2. Dieseling (run-on).
  3. Lack of power.
  4. Spark knock (pinging).
  5. Stalls/quits.
  6. Stumble/hesitation during acceleration.
  7. Misses/surges.
  8. Idle is fast/slow return to idle.
  9. Idle is rough.
  10. Engine speeds up.
  11. Cranks normally/no start.
  12. Cranks normally/slow to start.
  13. Poor fuel economy.
  14. Exhaust smoke/odor.
  15. Fuel odor/leaks.
  16. Fails emission test.

BACKFIRE THROUGH INDUCTION OR EXHAUST

  1. Check vane airflow meter.
  2. Check idle speed control solenoid.

DIESELING (RUN-ON)

  1. Check idle speed control solenoid.

LACK OF POWER

  1. Check vane airflow meter.
  2. Check throttle position switch.
  3. Check heated exhaust gas oxygen sensor.
  4. Check A/C switch.
  5. Check wide open throttle A/C (WAC) relay.

SPARK KNOCK (PINGING)

  1. Verify ignition timing is correct.
  2. Check vane airflow meter.

STALLS/QUITS

  1. Check vane airflow meter.
  2. Check idle speed control solenoid.
  3. Check pressure regulator control solenoid.
  4. Check heated exhaust gas oxygen sensor.
  5. Check engine coolant temperature sensor.
  6. Check A/C load control solenoid.

STUMBLE/HESITATION DURING ACCELERATION

  1. Check throttle position switch.
  2. Check vane airflow meter.
  3. Check canister purge solenoid.
  4. Check heated exhaust gas oxygen sensor.
  5. Check wide open throttle A/C (WAC) relay.
  6. Check A/C thermostatic switch.

MISSES/SURGES

  1. Check exhaust gas oxygen sensor.
  2. Check throttle position switch.
  3. Check vane airflow meter.
  4. Check wide open throttle vacuum switch.
  5. Check A/C load control solenoid.
  6. Check engine coolant temperature sensor.

IDLE IS FAST/SLOW RETURN TO IDLE

  1. Check idle speed control solenoid.
  2. Check by-pass air control valve.
  3. Check engine coolant temperature sensor.
  4. Check A/C load control solenoid.

IDLE IS ROUGH

  1. Check idle speed control solenoid.
  2. Check A/C load control solenoid.
  3. Check by-pass air control valve.
  4. Check throttle position switch.
  5. Check vane airflow meter.
  6. Check vane air temperature sensor.
  7. Check canister purge solenoid.
  8. Check engine cooling fan.
  9. Check headlight switch.
  10. Check blower control switch.
  11. Check A/C thermostatic switch.
  12. Check neutral safety switch.
  13. Check neutral gear switch or clutch engage switch.
  14. Check heated exhaust gas oxygen sensor.

ENGINE SPEEDS UP

  1. Check idle speed control solenoid.
  2. Check heated exhaust gas oxygen sensor.
  3. Check by-pass air control valve.

CRANKS NORMALLY/NO START

  1. Verify secondary ignition spark is present.
  2. Verify fuel pressure is within specification.
  3. Check vane airflow meter.
  4. Check engine coolant temperature sensor.

CRANKS NORMALLY/SLOW TO START

  1. Check ignition module.
  2. Check engine coolant temperature sensor.
  3. Check vane airflow meter.
  4. Check evaporative emission control components.

POOR FUEL ECONOMY

  1. Verify intake air is not restricted.
  2. Verify fuel pressure is within specification.
  3. Check ignition module.
  4. Check canister purge solenoid.
  5. Check vane air temperature sensor.
  6. Check vane airflow meter.
  7. Check heated exhaust gas oxygen sensor.

EXHAUST SMOKE/ODOR

  1. Check vane air temperature sensor.
  2. Check vane airflow meter.
  3. Check exhaust gas oxygen sensor.

FUEL ODOR/LEAKS

  1. Check evaporative emission control components.
  2. Check rollover vent valve.
  3. Check by-pass air control valve.

FAILS EMISSION TEST

  1. Check canister purge solenoid.
  2. Check pressure regulator control solenoid.
  3. Check heated exhaust gas oxygen sensor.
  4. Check by-pass air control valve.

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may lead to 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 changes on DVOM during test procedures indicate area of fault.

INTERMITTENT SIMULATION

To reproduce conditions creating an intermittent fault, use 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.

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