Allroad Quattro V8-4.2L (BAS) (2004)
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Pull vacuum hose (arrow) off fuel pressure regulator.
NOTE: If fuel flows out at the vacuum connection on the fuel pressure regulator during the following pressure test, install a new fuel pressure regulator.
Fuel pressure should increase to approx. 4.0 bar.
If specification is not obtained:
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Install a new pressure regulator as a trial measure and repeat pressure test.
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If fuel pressure still does not match specification, check fuel pump and supply line for damage (e.g. pinching) and replace if necessary.
If specification is obtained:
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Reconnect vacuum hose.
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Switch off ignition.
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Observe pressure drop on pressure gauge to check leakage and holding pressure.
After 10 minutes the pressure should still be at least 3 bar.
If the holding pressure drops below 3.0 bar:
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Start engine and run at idling speed.
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Switch ignition off after pressure has built up. Simultaneously close cutoff valve on pressure gauge V.A.G 1318 (valve handle at 90 5 to direction
of flow).
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Observe pressure drop on gauge.
If the pressure drops again, the following faults are possible:
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Unions on pressure gauge downstream of cut-off valve leaking
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Fuel pressure regulator faulty
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Injectors leaking
If the pressure does not drop, the following faults are possible:
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Union between pressure gauge and fuel supply line leaking
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Supply line leaking at fuel tank
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Non-return valve in fuel pump leaking.