Engine Controls - Basic Testing: Other Volkswagen Passat B4

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 O2 sensor or air injection check valve (if equipped). 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 SYSTEM APPLICATION

FUEL PRESSURE

Basic diagnosis of fuel system should begin with determining fuel system pressure.

Motronic MFI

1. Ensure ignition is off. Wrap cloth around fuel distributor port near cold start valve. Slowly loosen distributor port near cold start valve to release fuel pressure. Connect fuel pressure gauge between fuel distributor port and end of fuel line to cold start valve. Disconnect differential pressure regulator harness connector.
2. Start engine and let it run. System fuel pressure should 89-96 psi (6.3-6.7 kg/cm 2 ). If fuel pressure is greater than specification, go to next step. If system fuel pressure is less than specification, perform fuel volume check. If fuel volume is okay, replace fuel pressure regulator.
3. Remove return hose from pressure regulator and place in a container. Repeat test. If pressure is incorrect, replace fuel pressure regulator. If system pressure is okay, check for restricted fuel return line. Repair as necessary. Go to next step.
4. Turn ignition off. After 10 minutes, residual pressure should be 48 psi (3.4 kg/cm 2 ). After 20 minutes, residual pressure should be 46 psi (3.2 kg/cm 2 ). If system fuel pressure is low, check fuel pump check valve, sensor plate free play, fuel distributor "O" rings and seats. Replace if necessary. If these components are okay, replace fuel pressure regulator.

Transfer Pump Fuel Volume Check

1. Turn ignition off. To check transfer pump (in tank), remove rear seat. Remove fuel sending unit access cover. Disconnect ignition coil secondary wire and connect to ground.
2. With transmission in Neutral, crank engine for 3-4 seconds. While starter is turning and for a few seconds afterward, an audible sound should be heard at the pump. If sound is not heard, go to next step. If sound is heard, go to step 5).
3. Remove fuel pump relay from relay panel. Activate fuel pumps using Remote Control (VAG 1348/3A). If pump does not operate, remove transfer pump wire harness connector. (Scheme 8)
4. Using test light, check voltage between Brown wire and Red/Yellow wire. If voltage is present, replace transfer pump. If voltage is not present, repair open or short circuit in wiring.
5. Remove fuel pump relay jumper wire. Disconnect and plug transfer pump output hose. Attach a hose to pump outlet connector, and place other end of hose in a graduated container. Activate fuel pump for 10 seconds.
6. Minimum fuel flow should be 10 ounces (.3 liter). If fuel flow is low, check fuel tank filter for restriction. If fuel tank filter is okay, replace transfer pump.

Scheme 8

MAIN FUEL PUMP VOLUME CHECK

Note. Before testing main fuel pump, check transfer pump. See TRANSFER PUMP CHECK .

1. Remove fuel pump relay from relay panel. Activate fuel pumps using Remote Control (VAG 1348/3A). Measure voltage being applied to fuel pump when activating with remote control. Record voltage.
2. Fuel volume is relative to voltage applied to fuel pumps. Activate fuel pumps for 30 seconds. Compare volume with values in FUEL PUMP PERFORMANCE table.

FUEL PUMP PERFORMANCE (1)

IGNITION COIL

IGNITION COIL RESISTANCE - Ohms @ 68°F (20°C)

Hall Effect Sensor

1. Remove coil secondary wire and attach to ground. Disconnect Hall Effect sensor harness connector at distributor. Using an LED Test Light (US 1115), check for voltage between outer terminals of connector. (Scheme 9)and (Scheme 10). With ignition on, light should be on. If light is on, go to next step. If light is not on, check wiring for short or open circuit. If wiring is okay, replace ignition control unit.
2. Reconnect Hall Effect sensor harness connector. Pull back Hall Effect sensor boot to expose contact terminals. Connect LED Test Light (US 1115) probe to center contact and battery positive terminal. (Scheme 9) Observe test light while cranking engine. If test light blinks, Hall Effect sensor is okay. If light does not blink, replace Hall Effect sensor.

Voltage Supply & Ground To Hall Effect Sensor

1. With ignition off, disconnect Hall Effect sensor harness connector. Using a voltmeter, check for voltage between outer terminals No. 1 and 3. (Scheme 10) Turn ignition on. There should be a minimum of 4.5 volts (4-cylinder) or 10.0 volts (V6).
2. If there is no voltage, check for open wire between terminal No. 3 of Hall Effect sensor connector and ECM. Also check for voltage between terminal No. 1 of Hall Effect sensor and ground. Repair open and recheck.

Scheme 9

Voltage Supply & Ground To Power Stage

1. Turn ignition off. Disconnect coil power stage harness connector. Connect a voltmeter to terminals No. 1 and 3. see scheme 4
2. Turn ignition on. Ensure battery voltage is present. Turn ignition off. If voltage is not present, check for open wire from fuse box to terminal No. 1, or from terminal No. 3 to ground. Repair open wire and recheck.

Scheme 10

IDLE SPEED, CO LEVEL & IGNITION TIMING

Ensure idle speed, CO level and base ignition timing are set to specification. If necessary, see the ADJUSTMENTS article.

IDLE SPEED & MIXTURE

IDLE SPEED & CO LEVEL

IGNITION TIMING (Degrees BTDC @ RPM)

IGNITION TIMING ADVANCE (Degrees BTDC @ RPM)

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, go to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.