Audi Workshop Service and Repair Manuals

Note:

Fuel pressure regulator regulates fuel pressure as a function of intake pressure. As a result, the pressure drop at the injectors remains constant for each engine speed and load range.

Special tools and workshop equipment required

• ◆ V.A.G 1318 with V.A.G 1318/7, V.A.G 1318/8 and V.A.G 1318/15

Test requirements:

• ● Fuel pump relay OK; checking =>Page 24-53.
• ● Fuel pump OK; checking:

=> Fuel Supply - Petrol Engines; Repair group 20

• ● Fuel filter OK
• ● Battery voltage at least 12.7 V
• ● Vehicles with automatic gearbox: Selector lever in position P or N

• ‒ → Remove engine cover -arrows-.

Check system pressure

• ‒ → Connect pressure gauge V.A.G 1318 to fuel supply line using adapters 1318/7, 1318/8 (pressure hose) and 1318/15.
• ‒ Withdraw vacuum line from pressure regulator to induction manifold at pressure regulator and close off line.

Note:

Replace pressure regulator if fuel emerges at the vacuum connection of the pressure regulator in the course of the following pressure test.

• ‒ Start the engine and run at idling speed.

• ‒ Measure the fuel pressure.
• ‒ Specified value: 3.8...4.2 bar
• ‒ If specified value is not attained, try replacing the pressure regulator and repeating the pressure test.
• ‒ If specified value is still not attained, check the fuel pump/feed pipe for damage (e.g. crushing) and replace, if necessary.
• ‒ If specified value is exceeded, check the retardation pipe for damage (e.g. crushing) and replace, if necessary.

Note:

When performing the following test, do not leave the engine running for an unnecessarily long time with the vacuum hose detached, because the higher fuel pressure causes the fuel/air mixture to be enriched. This could lead to the lambda control limits to be exceeded, which would then result in a fault being recorded.

• ‒ Start the engine and run at idling speed.
• ‒ Switch off electrical consumption units (air conditioner system, etc).
• ‒ Attach vacuum hose to pressure regulator and observe drop in pressure on pressure gauge.

• ‒ Fuel pressure must decrease by approx. 0.5 bar when vacuum hose is attached.

• Perform the following checks if there is no change in pressure as described above:
• ‒ Check vacuum hose for cracks and damage.
• ‒ Check vacuum hose at intake manifold for blockage; to do so, pull off hose at pressure regulator and blow into it.

• ‒ If there is no leak and no blockage in the vacuum hose, replace the pressure regulator.

Checking holding pressure:

• ‒ Holding pressure 10 minutes after switching off engine (minimum pressure).
• ‒ Specified value for cold engine: approx. 2.2 bar
• ‒ Specified value with engine at operating temperature: approx. 3.0 bar

Note:

The increase in temperature with the engine at operating temperature is caused by the expansion of the fuel and is normal.

• ‒ Start the engine and run at idling speed.

• ‒ → Allow the pressure to build up, then switch off the ignition. At the same time close the cut off valve on the pressure gauge V.A.G 1318 (valve lever at right angles to direction of flow -arrow-).

If the pressure does not drop, the following faults are possible:

• ◆ Union between pressure gauge and fuel supply pipe leaking
• ◆ Supply pipe leaking at fuel tank
• ◆ Non-retardation valve in fuel pump leaking

=> Fuel Supply - Petrol Engines; Repair group 20

Note:

After the isolating valve has been closed, the pressure gauge shows the pressure after the isolating valve "induction manifold end" (direction of injectors, fuel pressure regulator). If the pressure before the isolating valve (tank direction) should now fall, the equipment cannot recognise this fact. For this reason, "If the pressure does not drop..." appears in the middle of this page.

If the pressure drops again, the following faults are possible:

• ◆ Fuel pressure regulator defective
• ◆ Injectors leaking
• ◆ Unions on pressure gauge after cut-off valve leaking

Note:

To remove the pressure gauge, close the shut-off valve, unscrew the union on adapter V.A.G 1318/15, then open the shut-off valve to drain off excess fuel into a suitable container.