System Pressure and Retaining Pressure (Vehicles As of 07.03), Checking

System Pressure And Retaining Pressure (vehicles As Of 07.03), Checking

NOTE: Fuel pressure regulator is integrated in fuel filter (under fuel tank) and cannot be replaced individually.

Recommended special tools and equipment

- Fuel Inj. Pressure Gauge Set V.A.G 1318 with adapters V.A.G 1318/6 and V.A.G 1318/7

Test requirements:
- Fuel Pump (FP) Relay OK; checking. Testing and Inspection
- Delivery quantity of Fuel Pump (FP) OK; check.
- Fuel filter OK
- Parking brake engaged.
- Vehicles with automatic transmission: Selector lever in P or N.
- Electrical consumers switched off (radiator fan must NOT run during test).
- A/C switched off.
- Ignition switched off.

Work procedure

- Remove rear engine cover (arrows).

Checking system pressure

WARNING: Fuel system is under pressure. Before opening system, place rags around the connection point. Then release pressure by carefully loosening connection.

- Open fuel filler flap briefly (pressure release).

- Remove fuel hose from connection on fuel rail line. To do so, counterhold at each hex head -1- and -3- using an open-end wrench and remove union nut -2-.

- Connect VAG1318 pressure gauge in supply line using adapters 1318/6 and 1318/7.

- Open shut-off valve of pressure gauge. The lever points in the direction of flow.
- Start engine and let run at idle.
- Measure fuel pressure.
- Specified value: 3.8 to 4.2 bar
- Switch ignition off.

Checking residual pressure
- Check for proper seal and residual pressure by observing pressure drop on pressure gauge.
- Specified value with a cold engine: approx. 2.2 bar
- Specified value with engine at operating temperature: approx. 3.0 bar

NOTE: Pressure increase for an engine at operating temperature limited by the fuel expansion is normal.

If residual pressure sinks below 2.2 / 3.0 bar positive pressure:
- Start engine and let run at idle.

- Wait until pressure has built-up, and then switch off ignition. Simultaneously close shutoff valve of VAG1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge.

If pressure drops again:
- Check pressure gauge for proper seal.
- Check line connections and fuel injectors for proper seal.

If pressure does not drop now:
- Check pressure regulator in fuel filter:
- Vehicles with Front Wheel Drive (FWD)
- Vehicles with All Wheel Drive (AWD)

- Replace fuel pump.

If pressure does not drop now:
- Replace fuel filter with integrated fuel pressure regulator.

Assembly is performed in the reverse order of removal. Note the following:

NOTE: Before disconnecting pressure gauge, release pressure by opening shut-off valve. Hold a container in front of connection for this.

- Remove cover for left connector flange (arrows).

- Disconnect fuel return line (arrow) from connector flange (left side of vehicle).

- Connect V.A.G 1318/17-1 adapter piece to return line.
- Pinch off adapter piece using 3094 hose clamps.

NOTE: 3094 hose clamps must not be placed directly on fuel line, otherwise it may be damaged.

- Start engine and let run at idle.

- Wait until pressure has built-up, and then switch off ignition. Simultaneously close shutoff valve of VAG1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge.

If pressure drops again, check-valve of fuel pump is leaky.
- Replace fuel pump.

If pressure does not drop now:
- Replace fuel filter with integrated fuel pressure regulator.

Assembly is performed in reverse order of removal. Note the following:

NOTE: Before disconnecting pressure gauge, release pressure by opening shut-off valve. Hold a container in front of connection for this.

- Secure fuel hose to connection on fuel rail line. To do so, counterhold at each hex head -1- and -3- using an open-end wrench and tighten union nut -2- to 22 Nm.

Checking fuel pressure regulator - Vehicles with Front Wheel Drive (FWD):

Limousine:
- Remove luggage compartment lining.
- Push forward the right backrest of rear seat, if necessary.

Avant:
- Remove left 1/3 backrest.
- Remove left side trim in luggage compartment and dirt tray.

All:

- Remove cover for connector flange (arrows).

- Disconnect fuel return line (arrow) (press release button).

- Wait until pressure has built-up, and then switch off ignition. Simultaneously close shutoff valve of VAG1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge.

If pressure drops again, check-valve of fuel pump is leaky.

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If DTC memory was erased, generate readiness code.

- End diagnosis and switch ignition off.