Audi S4 1994 - 1992-94 ENGINE PERFORMANCE Trouble Shooting - No Codes - S4

Audi S4 1994 - INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform preliminary inspection and steps in SELF-DIAGNOSTICS article. Use this article to diagnose driveability problems existing when a hard trouble code is not present.

NOTE:

Some driveability problems may have been corrected by manufacturer with a revised Engine Control Module (ECM). Check with manufacturer for latest ECM 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 SYSTEM & COMPONENT TESTING article. For specifications, see ADJUSTMENTS article.

Many computer-controlled and/or monitored components set a Diagnostic Trouble Code (DTC) if they malfunction. In this event testing is incorporated in self-diagnostics testing. For testing procedures, see SELF-DIAGNOSTICS article. For systems and components not covered in this article, use self-diagnostics testing procedures.

Audi S4 1994 - SYMPTOMS SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless problem occurs while vehicle is being tested.

• 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 S4 1994 - 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 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 S4 1994 - No Spark

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

Audi S4 1994 - DIFFICULT START (CRANKS OKAY)

• Ensure sufficient secondary spark is available.
• Check air induction system for cracks and restriction.
• Check airflow sensor plate rest position.
• 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.
• Check air temperature sensor operation (if equipped).
• Check engine coolant temperature sensor operation.
• Ensure electrical harness and connectors are not broken or loose.
• Ensure ECM or ignition control unit has correct voltage supply and is properly grounded.
• Ensure engine has sufficient compression.

Audi S4 1994 - 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 S4 1994 - 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 throttle valve switch.
• Check for EGR system malfunction (if equipped).
• Check operation of engine coolant temperature sensor.
• Check HO2S 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 S4 1994 - 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 engine coolant temperature sensor operation.

Audi S4 1994 - ENGINE STALLS

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

Audi S4 1994 - 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 engine 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 S4 1994 - 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 airflow sensor plate adjustment.
• Check airflow sensor voltage output.
• Check throttle valve switch.
• Check engine coolant temperature sensor operation.
• Check oxygen sensor (O2S) voltage output.

Audi S4 1994 - AFTERBURN IN EXHAUST SYSTEM

• Ensure no leaks exist in exhaust system.
• Check fuel injectors for leaking.
• Check coolant temperature sensor.

Audi S4 1994 - POOR FUEL MILEAGE

• Ensure base timing and timing advance system is functional.
• Ensure fuel system pressure is correct.
• Check airflow sensor voltage output.
• Check air induction system for leaks.
• Check fuel injector operation.
• Check engine coolant temperature sensor operation.
• Check oxygen sensor (O2S) operation.

Audi S4 1994 - 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 ECM application is correct.

Audi S4 1994 - FAILS EMISSION TEST

• Ensure engine is at normal operating temperature.
• Check crankcase for fuel contamination.
• Ensure base timing is correct.
• Check for correct crankcase ventilation system 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 sensor (O2S).
• Ensure fuel system pressure is correct.
• 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 S4 1994 - INTERMITTENTS 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.

Audi S4 1994 - 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 fault. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.