check engine AUDI A4 1998 B5 / 1.G AFC Engine Fuel Syst

24-20


Fuel system pressure and
residual pressure, checking

CAUTION!

Fire hazard! Do not smoke, work near heaters
or open flame, or have anything in the area
that could ignite fuel.

Checking requirements:

Fuel pump relay OK; checking page 24
-24

Fuel pump OK:

Repair Manual, 2.8 Liter V6 2V Engine
Mechanical, Engine Code(s): AFC, Repair Group 20


Correct fuel filter installed
Battery positive voltage (B+): 12 volts
minimum

Checking system pressure

-
Connect VAG 1318 pressure tester between fuel supply and fuel return
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24-21

- Use scan tool "Output Diagnostic Test Mode"
function 03 to trigger Fuel Pump (FP) relay -J17-
Repair Group 01. If fuel pump does not run:

- Check fuel pump:

Repair Manual, 2.8 Liter V6 2V Engine
Mechanical, Engine Code(s): AFC, Repair Group 20


Specified value: 3.8 to 4.2 bar (55 - 61 psi)
If the specified value is not obtained:

- Replace fuel pressure regulator and perform
pressure test again.
If the value is again not obtained:

- Check whether fuel pump or supply line is
damaged (e.g. pinched), and replace if
necessary.
If the specified value is exceeded:

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- Check return line for damage (e.g. pinched
locations), and replace if necessary.

Note:
During subsequent testing the engine should not
run for an unnecessarily long time with the
vacuum hose disconnected, because the
increased fuel pressure will cause mixture
enrichment which in turn may cause the oxygen
sensor control limits to be exceeded and a
malfunction to be registered and stored.
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24-22

- Let engine idle.

This will automatically halt the output DTM
sequence.

- Switch off all electrical consumers (A/C etc.).

- Connect vacuum hose to pressure regulator and
observe pressure drop on gauge.

Connecting the vacuum hose must reduce
fuel pressure by approx. 0.5 bar (7 psi)
If change in pressure does not occur:

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

- Check vacuum hose on intake manifold for flow
by disconnecting hose and blowing through it.
If there is no leakage and the vacuum connection
is open:

- Replace fuel pressure regulator.
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24-23

Residual pressure, checking
Residual pressure 10 minutes after stopping
engine:

With cold engine: 2.2 bar (32 psi) minimum
With a hot engine: 3.0 bar (44 psi) minimum

Note:
The pressure increase for a hot engine is caused
by fuel expansion and is normal.
If residual pressure is too low:

- Check pressure tester connections for leaks.

- Check fuel lines for leaks.

- Check fuel pump check valve:

Repair Manual, 2.8 Liter V6 2V Engine
Mechanical, Engine Code(s): AFC, Repair Group 20


- Check fuel injectors for leaks page 24
-33
.
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pressure and residual
pressure, checkin
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pair&id=AUDI.B5.FU01.24.4