fuel pressure AUDI A4 1999 B5 / 1.G APB Engine Motronic Multiport Fuel Injection System Servising User Guide

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
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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.
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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.
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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.
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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.
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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
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24-51

- Repeat test for fuel injectors from second bank
of cylinders.

- If measured values for all fuel injectors are
outside tolerance range (specification), check
fuel pressure Page 24
-33
.

Note:
When checking the injection quantity, also check
the spray pattern. The spray pattern should be
the same for all the injectors.
Installation of the fuel rail together with injectors
is performed in the reverse sequence. The
following points should be noted when installing:

Replace O-rings at all opened connections.
(When replacing the front O-ring, make sure
not to remove the plastic cap from the
injector head. The O-ring must be pulled off
over the plastic cap.)
Moisten O-rings with clean engine oil.
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24-53


Fuel rail with fuel injectors, dismantling
and assembling

1 -
Fuel rail
2 -
To intake manifold
3 -
Retaining clip
4 -
O ring
Replace
5 -
Fuel pressure regulator
6 -
O ring Replace
7 -
Injector (N30...N32, N33...N84)
8 -
Retaining clip Must be seated correctly at fuel injector
and fuel rail
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pair&id=AUDI.B5.FU04.24.1