1999 AUDI A4 fuel pressure

24-35

- If pressure is higher than specification, check
return pipe for damage (e.g. pinching) and
renew if necessary.

Note:
During the following test, do not allow the engine
to run for too long with the vacuum hose
disconnected, otherwise the increased fuel
pressure will enrich the air/fuel mixture and may
cause the lambda control limits to be exceeded.
This would be stored as a fault in the fault
memory.

- Start the engine and run at idling speed.

- Switch off electrical consumers (air conditioner
etc.).

- Re-connect vacuum hose to fuel pressure
regulator and observe drop in pressure on
pressure gauge.
Pa
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(MFI
) system, servicin
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24-36

- When the vacuum hose is re-connected the fuel
pressure should drop by around 0.5 bar.

If the pressure does not change as specified,
carry out the following tests:


Check vacuum hose for cracks and other
damage.

Test vacuum hose for blockages at intake
manifold. To do this, disconnect hose at fuel
pressure regulator and blow into it.

- If there are no leaks and no blockages in the
vacuum hose, install new fuel pressure
regulator.

- Replace hose clamp that secures vacuum hose
to the fuel pressure regulator and make sure
that new clamp is properly installed.

Checking residual fuel pressure

- Residual pressure 10 minutes after switching off
engine (minimum pressure)

With engine cold: at least 2.2 bar
Pa
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(MFI
) system, servicin
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24-37

Note:
A rise in pressure (due to fuel expansion) when
the engine is at operating temperature is normal.

- Start the engine and run at idling speed.

- Switch ignition off after the pressure has built-
up. At the same time close pressure gauge cut-
off tap (lever at 90 to through flow direction). 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
Return valve in fuel pump leaking

Repair Manual, Fuel Supply System, Repair
Group 20


Note:
When the cut-off tap is closed the pressure
gauge will indicate the pressure downstream of
Pa
ge 43 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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the cut-off tap, i.e. on the same side as the intake
manifold, injectors and fuel pressure regulator. If
there is then a drop in pressure upstream of the
cut-off tap (same side as fuel tank), the change
will not be registered by the pressure gauge. This
is why the paragraph beginning "If the pressure
does not drop..." has been included above.
Pa
ge 44 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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24-38
If the pressure drops again, the following
malfunctions are possible:

Fuel pressure regulator faulty
Fuel Injectors leaking
Unions on pressure gauge downstream of cut-
off valve leaking

Note:
When disconnecting the pressure gauge, close
the cut-off valve, unscrew the union on adapter
VAG 1318/15, then open the cut-off valve to
drain off excess fuel into a suitable container.
Pa
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port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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24-43

Fuel injection volume, fuel injector
leakage and spray pattern of injectors,
checking


WARNING!

Fire hazard! The fuel system is pressurized.
Before loosening hose connections or
opening the test connection (to measure fuel
pressure), place a cloth around the
connection. Then release pressure by
carefully pulling off the hose or cap.

Test conditions

Fuel pressure OK; testing Page 24
-33
.
To reach the fuel rail, the following steps must be
performed on vehicles with manual transmission
(without secondary air injection). On vehicles
with automatic transmission (with secondary air
injection) are minor differences in the work
procedure.

Several hoses must now be disconnected: - Unscrew bolts on air duct at points indicated (arrows) and remove air
duct.
- Absolute cleanliness must be maintained.
Pa
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(MFI
) system, servicin
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24-44


1 -
Detach Wastegate Bypass Regulator
Valve -N75 from fuel rail. The hoses must
remain connected.
2 -
Disconnect harness connector from EVAP
Canister Purge Regulator Valve -N80.
3 -
Disconnect harness connector from
Recirculating valve for turbocharger -
N249.
4 -
Open hose clamps shown in the
illustration and detach hoses from air
recirculating valve.
5 -
Open hose clamp on fuel pressure
regulator and detach hose.
6 -
Disconnect harness connectors from
injectors on cylinder banks 1 and 2.
Pa
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24-46


WARNING!
Fire hazard! The fuel system is pressurized.
Before loosening hose connections or opening
the test connection, place a cloth around the
connection. Then release pressure by carefully
pulling off the hose or cap. 10 -
Briefly open screw connection on fuel rail
(supply hose) to release pressure. Use
clean cloth to catch any fuel that leaks
out. Then tighten screw connection again.
11 -
Unbolt fuel rail from intake manifold at the
points indicated (see arrows).
Tightening torque bolts: 10 Nm
Pa
ge 55 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1