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Engine Controls - Tests W/o Codes Audi Cabriolet I

Testing & Diagnostics ~1401 words

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform preliminary inspection and steps in appropriate TESTS W/CODES article below. Use this article to diagnose driveability problems existing when a hard trouble code is not present.

  1. «TESTS W/CODES»(ref-9680) (for A6)
  2. «TESTS W/CODES»(/audi/cabriolet/i-1991-2000/remont/testing-diagnostics/#engine-controls-tests-wcodes) (for Cabriolet)
  3. «TESTS W/CODES»(ref-9684) (for 90)

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or Powertrain Control Module (PCM). Check with manufacturer for latest chip or PCM 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. See SYMPTOMS .

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. See INTERMITTENTS .

Note. For specific testing procedures, see apprpriate SYSTEM/COMPONENT TESTS article. below For specifications, see appropriate ADJUSTMENTS or SPECIFICATIONS articles below.

  1. «SPECIFICATIONS»(ref-9673) (for A6)
  2. «SPECIFICATIONS»(/audi/cabriolet/i-1991-2000/remont/specifications/#engine-controls-specifications) (for Cabriolet)
  3. «SPECIFICATIONS»(ref-9675) (for 90)
  4. «ADJUSTMENTS»(ref-9676) (for A6)
  5. «ADJUSTMENTS»(/audi/cabriolet/i-1991-2000/remont/adjustments/#engine-controls-adjustments) (for Cabriolet)
  6. «ADJUSTMENTS»(ref-9678) (for 90)
  7. «SYSTEM/COMPONENT TESTS»(ref-9693) (for A6)
  8. «SYSTEM/COMPONENT TESTS»(/audi/cabriolet/i-1991-2000/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) (for Cabriolet)
  9. «SYSTEM/COMPONENT TESTS»(ref-9695) (for 90)

SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate TESTS W/CODES article below were performed before diagnosing a symptom.

  1. «TESTS W/CODES»(ref-9680) (for A6)
  2. «TESTS W/CODES»(/audi/cabriolet/i-1991-2000/remont/testing-diagnostics/#engine-controls-tests-wcodes) (for Cabriolet)
  3. «TESTS W/CODES»(ref-9684) (for 90)

Following symptoms are available for diagnosis.

  1. Will Not Start (Cranks Okay)
  2. Difficult Start (Cranks Okay)
  3. Engine Surges
  4. Rough Or Unstable Idle
  5. Excessive Fast Idle
  6. Engine Stalls
  7. Engine Lacks Power
  8. Engine Misfires Or Hesitates
  9. Afterburn In Exhaust System
  10. Poor Fuel Mileage
  11. Detonation Or Knocking
  12. Fails Emission Test

Spark

  1. Check fuel system fuse and fuel pump relay.
  2. Verify air intake system is unrestricted.
  3. Ensure fuel system pressure and volume are correct.
  4. Check for poor quality or contaminated fuel.
  5. Check for condensation (water) in fuel tank, causing fuel pump to freeze (cold climate).
  6. Check exhaust system for restriction.

No Spark

  1. Ensure secondary ignition system is in good condition.
  2. Ensure ignition coil supply voltage is correct.
  3. Ensure ignition coil primary resistance is correct.
  4. Ensure ignition coil secondary resistance is correct.
  5. Check camshaft position sensor operation.
  6. Ensure PCM has correct voltage supply and is properly grounded.
  7. Check vehicle for aftermarket electronic equipment that may have been installed incorrectly.

DIFFICULT START (CRANKS OKAY)

  1. Ensure sufficient secondary spark is available.
  2. Check air induction system for cracks and restriction.
  3. Check airflow sensor plate rest position.
  4. Ensure vacuum hoses are not disconnected or damaged.
  5. Ensure fuel system pressure and volume are correct.
  6. Ensure fuel system residual pressure is correct.
  7. Ensure fuel injector operation is correct.
  8. Ensure EGR valve operation is correct.
  9. Check for cracks and poor connections at throttle body.
  10. Ensure ignition and valve timing are correct.
  11. Check ignition coil primary connections and wiring harness.
  12. Ensure ignition coil resistance is within specification.
  13. Check engine coolant temperature sensor operation.
  14. Ensure electrical harness and connectors are not broken or loose.
  15. Ensure PCM has correct voltage supply and is properly grounded.
  16. Ensure engine has sufficient compression.

ENGINE SURGES

  1. Ensure no vacuum leaks exist.
  2. Check for distortion and cracks in fuel injector plastic connecting flanges.
  3. Ensure EGR valve operation is correct.
  4. Check throttle position sensor operation.
  5. Check throttle shaft for excessive wear.
  6. Ensure fuel system pressure is correct and consistent.
  7. Ensure ignition timing is correct.

ROUGH OR UNSTABLE IDLE

  1. Ensure idle RPM is correct.
  2. Check air intake system for restrictions.
  3. Ensure fuel system pressure and volume are correct.
  4. Check fuel injector electrical connections.
  5. Use stethoscope to verify consistent operational noise coming from fuel injectors.
  6. Ensure fuel injector spray pattern is correct.
  7. Ensure sufficient secondary spark is available in all cylinders.
  8. Ensure vacuum hose routing is correct and no vacuum leaks exist.
  9. Check throttle position sensor operation.
  10. Check for EGR system malfunction.
  11. Check engine coolant temperature sensor operation.
  12. Check Heated Oxygen Sensor (HO2S) voltage output.
  13. Check for distortion and cracks in fuel injector plastic connecting flanges.
  14. Check for poor quality fuel.

Note. Prolonged use of poor quality fuel can cause injector clogging and carbon build-up on intake system.

EXCESSIVE FAST IDLE

  1. Check throttle cable adjustment.
  2. Ensure vacuum hose routing is correct.
  3. Ensure no vacuum leaks exist.
  4. Ensure fuel system pressure and volume are correct.
  5. Check engine coolant temperature sensor operation.

ENGINE STALLS

  1. Ensure air intake system is unrestricted.
  2. Ensure PCV system operation is correct.
  3. Check EGR system for correct operation.
  4. Check for distortion and cracks in fuel injector plastic connecting flanges.
  5. Check for cracks and poor connections at throttle body.
  6. Check throttle position sensor operation.
  7. Check engine coolant temperature sensor operation.
  8. Ensure fuel system pressure is correct.
  9. Check for poor quality fuel, fuel with high alcohol content or contaminated fuel.

ENGINE LACKS POWER

  1. Ensure throttle valve opens completely when accelerator pedal is fully depressed.
  2. Check for limited airflow sensor plate travel caused by defective screen in airflow sensor plate boot.
  3. Ensure air intake system is unrestricted.
  4. Ensure fuel system pressure and volume are correct.
  5. Ensure base timing is correct and timing advance system is functional.
  6. Check engine coolant temperature sensor operation.
  7. Check transmission for correct downshift (A/T).
  8. Check fuel tank filler tube for tampering of restrictor. If tampering has occurred, check catalytic converter for lead contamination and exhaust system restriction.
  9. Check for poor quality fuel containing insufficient cleaning additives.

Note. Prolonged use of poor quality fuel can cause injector clogging and carbon build-up on intake system.

ENGINE MISFIRES OR HESITATES

  1. Ensure vacuum hoses are not disconnected or damaged.
  2. Ensure electrical harness connectors and wires are not broken or loose.
  3. Ensure fuel pressure is correct.
  4. Check airflow sensor plate adjustment.
  5. Check airflow sensor voltage output.
  6. Check throttle position sensor operation.
  7. Check engine coolant temperature sensor operation.
  8. Check Heated Oxygen Sensor (HO2S) voltage output.

AFTERBURN IN EXHAUST SYSTEM

  1. Ensure no leaks exist in exhaust system.
  2. Ensure base timing system functions correctly.
  3. Check fuel injectors for leaking.
  4. Check engine coolant temperature sensor operation.

POOR FUEL MILEAGE

  1. Ensure base timing and timing advance system is functional.
  2. Ensure fuel system pressure is correct.
  3. Check airflow sensor voltage output.
  4. Check air induction system for leaks.
  5. Check fuel injector operation.
  6. Check engine coolant temperature sensor operation.
  7. Check Heated Oxygen Sensor (HO2S) voltage output.

DETONATION OR KNOCKING

  1. Check engine oil level.
  2. Check engine for overheating.
  3. Ensure base timing is correct.
  4. Check for vacuum leaks.
  5. Check EGR system operation.
  6. Check for contaminated or poor quality fuel.
  7. Check for carbon build-up in combustion chamber.
  8. Ensure spark plug application is correct.
  9. Check for correct torque of knock sensor.
  10. Check for correct knock sensor signal.
  11. Ensure PCM application is correct.

FAILS EMISSION TEST

  1. Ensure engine is at normal operating temperature.
  2. Check crankcase for fuel contamination.
  3. Ensure base timing is correct.
  4. Check for correct PCV valve operation.
  5. Check EGR system for correct operation.
  6. Ensure air intake system is not restricted.
  7. Check vapor recovery system operation.
  8. Check engine coolant temperature sensor operation.
  9. Check Heated Oxygen Sensor (HO2S) output voltage.
  10. Ensure fuel system pressure is correct.
  11. Check idle stabilizer operation.
  12. Check fuel tank filler tube for tampering of restrictor. If tampering has occurred, check catalytic converter for lead contamination and exhaust system restriction.
  13. Check for poor quality fuel containing insufficient cleaning additives.

Note. Prolonged use of poor quality fuel can cause injector clogging and carbon build-up on intake system.

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent trouble code testing requires duplicating circuit or component failure to identify problem. These procedures may lead to computer setting a trouble code which may help in diagnosis.

If vehicle does not produce trouble 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 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 fault. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.

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