1999 AUDI A4 engine

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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With engine at operating temperature: approx:
3.0 bar
Pa
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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
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port Fuel In
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24-39

Fuel injectors, checking


A - Electrical testing of fuel injectors

- Disconnect harness connector from injector to
be tested.

Note:
When the engine is at operating temperature the electrical resistance of
the injectors will be about 4 - 6 . higher.
If the specification is not obtained: - Connect hand-held multimeter to fuel injector (resistance measurement
range).

Specified value: 13.5 - 15.5 - Replace fuel injector Page 24
-53
. Also observe notes on Page
24
-51
.
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24-41

- Switch ignition on. The diode test lamp should
light up.

- If diode test lamp does not light up, test for open
circuits in wiring between contact 1 and fuse for
injectors. If necessary, rectify open circuit.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- If diode test lamp lights up, test activation of
injectors.

C - Testing activation of injectors

- Remove plug connector from the injector which
is to be tested.

Specified value: the diode test lamp should start flashing.
Note:
Diode test lamps with a low current draw continue to glow faintly between - Connect diode test lamp VAG 1527 between the battery positive
terminal (+) and contact 2 on the connector.
- Operate starter for a few seconds (the engine can be allowed to start).
Pa
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impulses from the engine control unit (rather than going out completely)
and become much brighter when receiving an impulse.
Pa
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24-42
If the diode test lamp does not flash:

- Connect test box VAG 1598/31 to wiring
harness for engine control unit. Do not connect
to the engine control unit itself. Page 24
-20
.

- Test for open circuit or short to B+ in wiring between engine control
module and contact 2 on harness connector for fuel injector being
tested.
Contact 2 on
connector for injector,
Cylinder No. Test box VAG 1598/31, socket
1 96
2 112
3 88
4 97
5 113
6 89
- Rectify short circuit or open circuit if necessary.
- If wiring is OK, install a new engine control module Page 24
-24
.
Pa
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24-47

- Lift fuel rail off intake manifold together with fuel
injectors and support the fuel rail.

Note:

After lifting off the fuel rail, check to make sure
that the injectors are properly secured to the
fuel rail.
It is possible that some of the fuel injectors will
become detached from the fuel rail and remain
in the intake manifold when the fuel rail is
removed. If this happens, install the fuel
injectors back onto the fuel rail Page 24
-53
.

WARNING!
Make sure test box is inside of passenger compartment. - Connect test box VAG 1598/31 to wiring harness for engine control
unit. Do not connect to the engine control module itself Page 24
-20
.
Pa
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port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1