fuel pressure AUDI A4 1998 B5 / 1.G AHA Engine Multiport Fuel Injection And Ignition System User Guide

24-113
If the specified value is not attained:

- Replace fuel pressure regulator and repeat
pressure test.
If the specified value is still not obtained:

- Check fuel pump or supply line for damage (e.g.
pinched locations); replace if necessary.
If the specified value is exceeded:

- Check return line for damage (e.g. pinch
locations); replace if necessary.

- Install vacuum hose on fuel pressure regulator
and check for pressure drop on gauge.

Specification: when vacuum hose is installed,
fuel pressure must drop by about 0.5 bar (7 psi).
If pressure does not change, the following tests
should be conducted:

- Check vacuum line for leaks (cracks,
damage).

-
Check vacuum line at intake hose for
obstruction; remove hose at fuel pressure
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24-114
If there is no leak and vacuum connection has no
obstruction:

- Replace fuel pressure regulator.

Checking residual pressure

- Check residual pressure 10 minutes after
shutting off engine.


Cold engine (min.): approx. 2.2 bar (31.9
psi)

Warm engine (min.): approx. 3.0 bar (43.5
psi)

Note:
The higher pressure with a warm engine, caused
by fuel expansion, is normal.
If the specified value is not attained:

- Start engine and, after fuel pressure has
increased, switch ignition off.

- Close shut off valve on VAG1318 pressure
tester.
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24-115
If the residual pressure drops (is lower than
spec.) again, the following malfunctions are
possible.

Connections for the pressure gauge and fuel
lines leaking
Pre-feed line on fuel reservoir leaking
Check valve in the electric fuel pump
malfunctioning

Repair Manual, Fuel Supply System, Repair
Group 20, Checking fuel pump check valve

If retaining pressure does not drop, the following
malfunctions are possible:

Malfunctioning fuel pressure regulator
Injectors leaking
Connections for the pressure gauge leaking
behind shut-off valve

Note:
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port Fuel In
jection
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To remove the pressure gauge, close the shut-off
valve, loosen the connection on the VAG1318/12
adapter and drain excess fuel by opening the
shut-off valve into collector container.
Pa
ge 150 of 166 Motronic Multi
port Fuel In
jection
(MFI
) and i
gnition s
ystem
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU03.24.1