Audi 100 1993 - H - TESTS W/O CODES ENGINE PERFORMANCE Trouble Shooting - No Codes

Audi 100 1993 - INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform the basic steps in the BASIC TESTING article and also perform the self-diagnostic procedures in the TESTS W/CODES article. Use this article to diagnose driveability problems that exist when a hard fault code is not present or when 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 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 component testing procedures, refer to the SYSTEM/COMPONENT TESTS article. For engine performance related specifications, see the ADJUSTMENTS article or the SPECIFICATIONS article.

Audi 100 1993 - SYMPTOMS SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure BASIC steps in the BASIC TESTING article and that the self-diagnostic test procedures in the TESTS W/CODES article were performed before diagnosing a symptom. The following symptoms are available for diagnosis in this article.

• Will Not Start (Cranks Okay)
• Difficult Start (Cranks Okay)
• Engine Surges
• Rough Or Unstable Idle
• Excessive Fast Idle
• Engine Stalls
• Engine Lacks Power
• Engine Misfires Or Hesitates
• Afterburn In Exhaust System
• Poor Fuel Mileage
• Detonation Or Knocking
• Fails Emission Test

Audi 100 1993 - WILL NOT START (CRANKS OKAY) Spark

• Check ignition fuse (if equipped).
• Check fuel system fuse and fuel pump relay.
• Verify air intake system is unrestricted.
• Ensure fuel system pressure and volume are correct.
• Check cold start valve operation (engine cold).
• Check for poor quality or contaminated fuel.
• Check for condensation (water) in fuel tank, causing fuel pump to freeze (cold climate).
• Check exhaust system for restriction.

Audi 100 1993 - No Spark

• Ensure secondary ignition system is in good condition.
• Ensure ignition coil supply voltage is correct.
• Ensure ignition coil primary resistance is correct.
• Ensure ignition coil secondary resistance is correct.
• Check hall sender operation.
• Check ignition control unit.
• Ensure computer has correct voltage supply and is properly grounded.
• Check vehicle for aftermarket electronic equipment that may have been installed incorrectly.

Audi 100 1993 - DIFFICULT START (CRANKS OKAY)

• Ensure sufficient secondary spark is available.
• Check air induction system for cracks and restriction.
• Check airflow sensor plate rest position.
• Check cold start valve for leaking (engine warm).
• Ensure vacuum hoses are not disconnected or damaged.
• Ensure fuel system pressure and volume are correct.
• Ensure fuel system residual pressure is correct.
• Ensure fuel injector operation is correct.
• Ensure EGR valve operation is correct (if equipped).
• Check for cracks and poor connections at throttle body.
• Ensure ignition and valve timing are correct.
• Check ignition coil primary connections and wiring harness.
• Ensure ignition coil resistance is within specification.
• Check air temperature sensor operation (if equipped).
• Check coolant temperature sensor operation.
• Ensure electrical harness and connectors are not broken or loose.
• Ensure ECU or ignition control unit has correct voltage supply and is properly grounded.
• Ensure engine has sufficient compression.

Audi 100 1993 - ENGINE SURGES

• Ensure no vacuum leaks exist.
• Check for distortion and cracks in fuel injector plastic connecting flanges.
• Ensure EGR valve operation is correct (if equipped).
• Check throttle valve switch.
• Check throttle shaft for excessive wear.
• Ensure fuel system pressure is correct and consistent.
• Ensure ignition timing is correct.

Audi 100 1993 - ROUGH OR UNSTABLE IDLE

• Ensure idle RPM is correct.
• Check air intake system for restrictions.
• Check auxiliary air by-pass regulator.
• Ensure fuel system pressure and volume are correct.
• Check fuel injector electrical connections.
• Use stethoscope to verify consistent operational noise coming from fuel injectors.
• Ensure fuel injector spray pattern is correct.
• Ensure sufficient secondary spark is available in all cylinders.
• Ensure vacuum hose routing is correct and no vacuum leaks exist.
• Check cold start valve for leaking (engine warm).
• Check throttle valve switch.
• Check for EGR system malfunction (if equipped).
• Check operation of coolant temperature sensor.
• Check O2 sensor operation.
• Check for distortion and cracks in fuel injector plastic connecting flanges.
• Check for poor quality fuel.

NOTE:

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

Audi 100 1993 - EXCESSIVE FAST IDLE

• Check throttle cable adjustment.
• Ensure vacuum hose routing is correct.
• Ensure no vacuum leaks exist.
• Ensure fuel system pressure and volume are correct.
• Check auxiliary air by-pass regulator.
• Check cold start valve for leaking (engine warm).
• Check coolant temperature sensor operation.

Audi 100 1993 - ENGINE STALLS

• Ensure air intake system is unrestricted.
• Ensure PCV system operation is correct.
• Check EGR system for correct operation.
• Check for distortion and cracks in fuel injector plastic connecting flanges.
• Check for cracks and poor connections at throttle body.
• Check auxiliary air by-pass regulator.
• Check cold start valve for leaking (engine warm).
• Check throttle valve switch.
• Check coolant temperature sensor operation.
• Ensure fuel system pressure is correct.
• Check for poor quality fuel, fuel with high alcohol content or contaminated fuel.

Audi 100 1993 - ENGINE LACKS POWER

• Ensure throttle valve opens completely when accelerator pedal is fully depressed.
• Check for limited airflow sensor plate travel caused by defective screen in airflow sensor plate boot.
• Ensure air intake system is unrestricted.
• Ensure fuel system pressure and volume are correct.
• Ensure base timing is correct and timing advance system is functional.
• Check coolant temperature sensor operation.
• Check transmission for correct downshift (A/T).
• Check fuel tank filler tube for tampering of restrictor. If tampering has occurred, check catalytic converter for lead contamination and exhaust system restriction.
• 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.

Audi 100 1993 - ENGINE MISFIRES OR HESITATES

• Ensure vacuum hoses are not disconnected or damaged.
• Ensure electrical harness connectors and wires are not broken or loose.
• Ensure fuel pressure is correct.
• Check cold start valve for leaking (engine warm).
• Check airflow sensor plate adjustment.
• Check airflow sensor voltage output.
• Check throttle valve switch.
• Check coolant temperature sensor operation.
• Check oxygen (O2) sensor voltage output.

Audi 100 1993 - AFTERBURN IN EXHAUST SYSTEM

• Ensure no leaks exist in exhaust system.
• Ensure base timing system functions correctly.
• Check fuel injectors for leaking.
• Check cold start valve operation.
• Check coolant temperature sensor.

Audi 100 1993 - POOR FUEL MILEAGE

• Ensure base timing and timing advance system is functional.
• Ensure fuel system pressure is correct.
• Check cold start valve for leaking (engine warm).
• Check airflow sensor voltage output.
• Check air induction system for leaks.
• Check fuel injector operation.
• Check engine coolant temperature sensor operation.
• Check oxygen (O2) sensor operation.

Audi 100 1993 - DETONATION OR KNOCKING

• Check engine oil level.
• Check engine for overheating.
• Ensure base timing is correct.
• Check for vacuum leaks.
• Check EGR system operation (if equipped).
• Check for contaminated or poor quality fuel.
• Check for carbon build-up in combustion chamber.
• Ensure spark plug application is correct.
• Check for correct torque of knock sensor (if equipped).
• Check for correct knock sensor signal (if equipped).
• Ensure ECU application is correct.

Audi 100 1993 - FAILS EMISSION TEST

• Ensure engine is at normal operating temperature.
• Check crankcase for fuel contamination.
• Ensure base timing is correct.
• Check for correct PCV valve operation.
• Check EGR system (if equipped) for correct operation.
• Ensure air intake system is not restricted.
• Check vapor recovery system operation.
• Check operation of coolant temperature sensor.
• Check operation of oxygen (O2) sensor.
• Ensure fuel system pressure is correct.
• Check cold start valve for leaking (engine warm).
• Check thermo time switch operation.
• Check idle stabilizer operation.
• Check fuel tank filler tube for tampering of restrictor. If tampering has occurred, check catalytic converter for lead contamination and exhaust system restriction.
• 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.

Audi 100 1993 - INTERMITTENTS 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 which may help in diagnosis.

If 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 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.

Audi 100 1993 - TEST PROCEDURES Intermittent Simulation

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

• Lightly vibrate component.
• Heat component.
• Wiggle or bend wiring harness.
• Spray component with water.
• 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.