Engine Controls - Basic Testing Audi A4 B5

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition. The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.

Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.

VISUAL INSPECTION

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not pinched or cut. See VACUUM DIAGRAMS article to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions.

COMPRESSION SPECIFICATIONS

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. Remove oxygen sensor. Connect a 0-5 psi pressure gauge and operate engine at 2500 RPM. If exhaust system backpressure is greater than 2 psi, exhaust system or catalytic converter is plugged.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.

FUEL SYSTEM

FUEL PRESSURE RELEASE

Remove fuel pump relay. Start engine. Allow engine to run until it stalls. Turn ignition off. Disconnect negative battery cable. Slight pressure may remain in system. Before disconnecting any fuel system line, cover connector with a clean shop towel. Reinstall fuel pump relay.

FUEL PRESSURE TEST

Note. Volkswagen Audi Group (VAG 1551) scan tool is necessary to activate fuel system for fuel pressure test.

Fuel System Pressure

1. Ensure fuel pump relay is okay. Ensure correct fuel filter is installed. Ensure battery voltage is at least 12 volts. Release fuel pressure. Ensure ignition is off.
2. Connect Pressure Gauge (VAG 1318) between fuel supply and fuel return lines in engine compartment. Disconnect and plug vacuum line from fuel pressure regulator. Following VAG 1551 scan tool manufacturer's instructions, energize fuel system.
3. Fuel pressure should be 55-61 psi (3.8-4.2 bar). If fuel pressure is within specification, perform FUEL SYSTEM RESIDUAL PRESSURE test BELOW. If fuel pressure is not within specification, replace fuel pressure regulator and perform test again.
4. If fuel pressure is not within specification after replacing fuel pressure regulator, check for damaged fuel pump or damaged fuel lines. Repair as necessary. If fuel pressure is more than specification after replacing fuel pressure regulator, check fuel return line for damage. Repair as necessary.

Fuel System Residual Pressure

1. Tee fuel pressure gauge into fuel supply line. Start engine and let it idle. With cold engine, minimum residual fuel pressure specification is 32 psi (2.2 bar). With hot engine, minimum residual fuel pressure specification is 44 psi (3.0 bar).
2. If residual fuel pressure is minimum or more, residual fuel pressure is okay. If residual fuel pressure is less than minimum, check fuel lines for leaks and repair as necessary. Check fuel injectors for leaks. See «FUEL INJECTOR TEST»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-basic-testing) . Check fuel pump check valve for malfunction. See «FUEL PUMP CHECK VALVE TEST»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-basic-testing__fuel-pump-check-valve-test) .

Fuel Injector Leak Test

1. Ensure fuel system pressure is within specification before performing this test. Remove fuel rail complete with fuel injectors from engine. DO NOT disconnect fuel supply or return lines. Using VAG 1551 scan tool, energize fuel pump.
2. With fuel pump running, visually inspect fuel injector for leaks. Maximum allowable leakage is 1-2 drops of fuel per injector per minute. If fuel injector leaks more than 2 drops of fuel per minute, replace leaking fuel injector. ALWAYS replace fuel injector "O" rings.

Fuel Injector Resistance Test

Turn ignition off. Disconnect fuel injector electrical connector. Using a DVOM, measure resistance across fuel injector terminals. See INJECTOR RESISTANCE table. If resistance is not within specification, replace fuel injector.

INJECTOR RESISTANCE

Fuel Injector Quantity Test

1. Remove fuel rail, complete with fuel injectors, from engine. DO NOT disconnect fuel supply or return lines. Place fuel injector being tested into a graduated container. Connect one terminal of fuel injector to battery positive terminal.
2. Connect other terminal of fuel injector to ground for exactly 30 seconds. Fuel quantity should be 2.9-3.7 oz. (85-110 ml). If fuel quantity is more than or less than specification, replace faulty fuel injector.

FUEL PUMP CHECK VALVE TEST

1. Connect Pressure Gauge (VAG 1318) between fuel supply and fuel return lines in engine compartment. Ensure pressure gauge test valve is in OPEN position.
2. Operate remote control switch for approximately 30 seconds. Move pressure gauge test valve to CLOSED position. Briefly operate remote control switch until maximum of 80 psi (5.5 bar) is indicated. Observe pressure drop on fuel pressure gauge.
3. After 10 minutes, maximum allowable pressure drop is 7 psi (.5 bar). If pressure drop is more than allowable maximum, ensure no fuel leaks are present in fuel lines. If no fuel leaks are present in fuel lines, fuel pump check valve is defective. Replace fuel pump.

IGNITION SYSTEM

Note. Perform spark test before performing other ignition checks.

SPARK TEST

Note. When ignition coil is triggered, spark is supplied to 2 spark plugs at one time. One spark plug fires during compression stroke and the other plug fires during exhaust stroke (waste spark).

Check for a strong Blue spark at coil wire and at each spark plug wire by holding wire terminal no more than 1/4" from chassis ground while cranking engine. Disconnect and inspect all related ignition system connectors and harness. Clean or repair as necessary.

Checking Voltage Supply

1. Turn ignition off. Disconnect Camshaft Position (CMP) sensor 3-pin connector. CMP sensor is located at rear of left cylinder head. Turn ignition on. Connect a DVOM between CMP sensor connector terminals No. 1 and 3. (Scheme 17)
2. Voltage should be 9 volts. If voltage is not to specification, repair open or short in wiring harness between CMP sensor connector and Powertrain Control Module (PCM). See «WIRING DIAGRAMS»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-basic-testing) section.

Scheme 17

Checking Resistance

1. Disconnect Crankshaft Position (CKP) sensor connector (located on left side of cylinder block). Using a DVOM, measure resistance between CKP sensor connector (sensor side) terminals No. 1 and 2. (Scheme 18)
2. Resistance should be approximately 1000 ohms. If resistance is not to specification, replace CKP sensor. If resistance is to specification, go to next step.
3. Connect DVOM between CKP sensor connector (sensor side) terminals No. 1 and 3, then terminals No. 2 and 3. Resistance should be infinite (open). If resistance readings are not infinite, replace CKP sensor.

Scheme 18

Ignition Coil Primary Resistance

Disconnect ignition coil 3-pin connector (located in front of intake manifold). Disconnect ignition coil power output stage 3-pin connector (located on right side of engine compartment). (Scheme 19) Measure resistance between any terminal of ignition coil 3-pin connector and power output stage 3-pin connector terminal No. 3. (Scheme 17)and (Scheme 18). Maximum allowable resistance is 5 ohms. If resistance is not within specification for any coil, replace ignition coil assembly.

Scheme 19

Ignition Coil Secondary Resistance

Disconnect spark plug wires from ignition coil being tested. Measure resistance between coil towers of ignition coil being tested. If resistance is 9000-14,000 ohms, coil secondary circuit is okay. If resistance is not 9000-14,000 ohms, replace coil.

Ignition Coil Voltage Supply

Ensure fuse for ignition coils is okay. Turn ignition off. Disconnect White ignition coil voltage supply connector. (Scheme 20) Turn ignition on. Using a DVOM, measure voltage between ground and all 3 terminals of White ignition coil voltage supply connector. Voltage should be approximately battery voltage. If voltage is not to specification, repair wiring harness as necessary.

Scheme 20

Note. Before performing this test, ensure fuses for ignition coils are okay and ignition coil resistance is okay.

Ignition Coil Output Stage Voltage Check

Disconnect power output stage 3-pin connector (located on right side of engine compartment). (Scheme 19) Turn ignition on. Using a DVOM, measure voltage between each connector terminal and ground. Voltage should be approximately battery voltage. If voltage is not to specification, repair wiring harness as necessary.

Ignition Coil Output Stage Ground Check

Disconnect power output stage 4-pin connector (located on right side of engine compartment). (Scheme 19) Turn ignition on. Using a DVOM, measure voltage between power output stage 4-pin connector terminal No. 2 and battery voltage. (Scheme 21) Voltage should be approximately battery voltage. If voltage is not to specification, repair wiring harness as necessary.

Scheme 21

IDLE SPEED & IGNITION TIMING

Idle speed, ignition timing and ignition timing advance are controlled by the PCM and are not adjustable.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to appropriate TESTS W/CODES article. If no hard codes are found in self-diagnostics, SEE TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

Wiring Diagram (A4 2.8L - 1 Of 2). Scheme 22

Wiring Diagram (A4 2.8L - 2 Of 2). Scheme 23

See also:
• TESTS W/CODES
• TESTS W/O CODES
• FUEL INJECTOR TEST
• FUEL PUMP CHECK VALVE TEST