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Engine Controls - Tests W/o Codes Porsche 911 Carrera 964

Testing & Diagnostics ~934 words

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in the BASIC TESTING article and also in the appropriate TESTS W/CODES article. 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 or system test, or 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 the article SYSTEM/COMPONENT TESTS . For specifications, see SPECIFICATIONS For adjustment procedures, see ADJUSTMENTS

SYMPTOMS LIST

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

  1. Engine Will Not Start
  2. Engine Hard To Start
  3. Erratic Idle
  4. Poor Pick-Up (Acceleration)
  5. Misfire
  6. High Fuel Consumption
  7. Engine Hesitation
  8. Poor Power Output
  9. Poor Hot Starting
  10. Diagnosis Not Possible

ENGINE WILL NOT START

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check DME relay.
  5. Check voltage to DME control unit.
  6. Check ground circuits and connectors.
  7. Check engine (coolant) temperature sensor and circuit.
  8. Check engine speed/reference mark sensor and circuit.
  9. Check idle speed control activation circuit.
  10. Check fuel injector(s) and circuit(s).
  11. Check DME control unit.

ENGINE HARD TO START

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check DME relay.
  5. Check ground circuits and connectors.
  6. Check idle switch and circuit.
  7. Check idle speed control activation circuit.
  8. Check engine (coolant) temperature sensor and circuit.
  9. Check engine speed/reference mark sensor and circuit.
  10. Check fuel tank venting solenoid.
  11. Check fuel injector(s) and circuit(s).
  12. Check DME control unit.

ERRATIC IDLE

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check DME relay.
  5. Check ground circuits and connectors.
  6. Check oxygen sensor and circuit.
  7. Check oxygen regulation stop circuit.
  8. Check airflow sensor and circuit.
  9. Check idle switch and circuit.
  10. Check idle speed control activation circuit.
  11. Check intake air temperature sensor and circuit.
  12. Check engine (coolant) temperature sensor and circuit.
  13. Check fuel tank venting solenoid.
  14. Check fuel injector(s) and circuit(s).
  15. Check DME control unit.

POOR PICK-UP (ACCELERATION)

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check DME relay.
  5. Check ground circuits and connectors.
  6. Check oxygen sensor and circuit.
  7. Check oxygen regulation stop circuit.
  8. Check airflow sensor and circuit.
  9. Check intake air temperature sensor and circuit.
  10. Check engine (coolant) temperature sensor and circuit.
  11. Check engine speed/reference mark sensor and circuit.
  12. Check Hall Effect sensor and circuit.
  13. Check fuel tank venting solenoid.
  14. Check fuel injector(s) and circuit(s).
  15. Check DME control unit.

MISFIRE

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check ground circuits and connectors.
  5. Check charging system voltage.
  6. Check voltage to DME control unit.
  7. Check oxygen sensor and circuit.
  8. Check oxygen regulation stop circuit.
  9. Check airflow sensor and circuit.
  10. Check engine speed/reference mark sensor and circuit.
  11. Check fuel tank venting solenoid.
  12. Check fuel injector(s) and circuit(s).
  13. Check DME control unit.

HIGH FUEL CONSUMPTION

  1. Check fuel pressure.
  2. Check intake system for leaks.
  3. Check oxygen sensor and circuit.
  4. Check oxygen regulation stop circuit.
  5. Check idle switch and circuit.
  6. Check full throttle switch and circuit.
  7. Check intake air temperature sensor and circuit.
  8. Check engine (coolant) temperature sensor and circuit.
  9. Check airflow sensor and circuit.
  10. Check resonance plate.
  11. Check Hall Effect sensor and circuit.
  12. Check knock sensors and circuits.
  13. Check fuel injector(s) and circuit(s).
  14. Check DME control unit (knock control).

ENGINE HESITATION

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check DME relay.
  5. Check oxygen sensor and circuit.
  6. Check oxygen regulation stop circuit.
  7. Check full throttle switch and circuit.
  8. Check intake air temperature sensor and circuit.
  9. Check engine (coolant) temperature sensor and circuit.
  10. Check engine speed/reference mark sensor and circuit.
  11. Check airflow sensor and circuit.
  12. Check Hall Effect sensor and circuit.
  13. Check knock sensors and circuits.
  14. Check fuel injector(s) and circuit(s).
  15. Check DME control unit (knock control).

POOR POWER OUTPUT

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check DME relay.
  5. Check ground circuits and connectors.
  6. Check charging system voltage.
  7. Check voltage to DME control unit.
  8. Check oxygen sensor and circuit.
  9. Check oxygen regulation stop circuit.
  10. Check idle switch and circuit.
  11. Check intake air temperature sensor and circuit.
  12. Check engine (coolant) temperature sensor and circuit.
  13. Check engine speed/reference mark sensor and circuit.
  14. Check airflow sensor and circuit.
  15. Check fuel tank venting solenoid.
  16. Check fuel injector(s) and circuit(s).
  17. Check DME control unit.

POOR HOT STARTING

  1. Check fuel pressure.
  2. Check ignition system.
  3. Check intake system for leaks.
  4. Check DME relay.
  5. Check oxygen sensor and circuit.
  6. Check oxygen regulation stop circuit.
  7. Check idle speed control activation circuit.
  8. Check intake air temperature sensor and circuit.
  9. Check engine (coolant) temperature sensor and circuit.
  10. Check engine speed/reference mark sensor and circuit.
  11. Check fuel tank venting solenoid.
  12. Check fuel injector(s) and circuit(s).
  13. Check DME control unit.

DIAGNOSIS NOT POSSIBLE

  1. Check voltage to DME control unit.
  2. Check ground circuits and connectors.
  3. Check diagnostic connector inputs to DME control unit.
  4. Check DME control unit.

Poses Online

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