checking AUDI A8 1996 D2 / 1.G AHA Engine Multiport Fuel Injection And Ignition System Service Manual

24-110

Checking for leaks

- Conduct output DTM, actuating cylinder 1
injector -N30- page 01
-51
(fuel pump must be
running).

Note:
This step lets the fuel pump run without the
engine running. The closed throttle position
switch must be closed during the test, or the
selected fuel injector will discharge fuel when it is
actuated 5 times.

- Visually check injector for leaks.

With fuel pump running, only 1 to 2 drops can
drip in a minute (per injector).
If fuel loss is greater:

- Replace leaking injector
Installation of the injectors is in reverse order of
removal.

- Replace O-rings on all injectors and coat O-rings
lightly with clean engine oil.

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24-111

Fuel pressure, fuel pressure regulator
and residual fuel pressure, checking

The fuel pressure regulator controls the fuel
pressure depending on intake manifold
pressure.

WARNING!

Fire hazard! Do not smoke, work near heaters
or open flame, or have anything nearby that
could ignite fuel. The fuel system is under
pressure. Before opening, cover connections
with a rag, and open carefully to release
pressure.

Required special tools and test equipment

Pressure tester VAG1318
Adapter 1318/7
Adapter 1318/10
Adapter 1318/13

Test requirements
Fuel pump delivery rate OK; checking:
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24-112

Checking

Note:
Shut-off valve of pressure tester must be open (lever parallel to direction
of flow).
Note:
For the following test, do not let the engine run unnecessarily with the
vacuum hose removed, since the higher fuel pressure causes enrichment
of the fuel air mixture. The richer mixture could exceed the O2S control
limits and therefore cause a DTC to be stored.
Note:
If, during the following pressure test, fuel leaks from the vacuum
connection of the fuel pressure regulator, replace the fuel pressure
regulator. - Connect pressure tester VAG1318 between fuel supply line and fuel
rail using adapters 1318/7, 1318/10 and 1318/13.
- Remove vacuum line from fuel pressure regulator (to intake manifold)
and block line (using VW 3093).
- Switch off all electrical consumers (rear defrost, A/C etc.).
- Start engine and let idle.
- Measure 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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24-116

Evaporative Emissions (EVAP) canister
purge regulator valve, checking


WARNING!

Whenever carrying out work on the fuel
supply and/or fuel injection systems, read
and carefully follow the Cautions, Warnings,
and rules of cleanliness page 24-9 .

Note:
Component locations page 24
-1

Required special tools and test equipment

VAG1551 or VAG1552 Scan Tool (ST) with
VAG1551/3 adapter cable

Test conditions
Engine coolant temperature at least 80 C
(176 F)

Function check

- Connect VAG1551 or VAG1552 scan tool and
press buttons -0- and -1- to insert "Engine
Electronics" address word 01 (with engine
running at idle) page 01
-8 .
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24-119

Checking for blockage and leaks
The EVAP canister purge regulator valve is
closed when power is off.

- Remove EVAP canister purge regulator valve -
N80- (component locations page 24
-1 )

- Connect removed valve to harness connector.

- Start output Diagnostic Test Mode (DTM) and
select -N80- page 01
-51
.

- Blow into long connection during output DTM,
and check whether valve opens and closes
properly. Replace valve if necessary.
If valve -N80- does not open and close as
specified:

- Replace -N80-.
If valve -N80- is OK:

- Check all hose connections between tank and
valve for blockage or leaks.
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24-121

Checking EVAP canister purge regulator
valve voltage supply

Test conditions

Fuse for EVAP canister purge regulator
valve OK

- Disconnect harness connector from EVAP
canister purge regulator valve.

If LED test light does not light:
If wiring is OK: - Connect VAG1527B LED voltage tester between connector terminal 1
(B+) and engine Ground.
- Operate starter motor.
Specified value: LED must light up
- Check wiring for open circuit between connector terminal 1 and fuse,
according to wiring diagram; repair if necessary.

Specified value: 1.0 max.- Check fuel pump relay page 24
-95
.
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24-122

Checking signal to EVAP canister purge
regulator valve

If LED test light does not blink, or stays on:
If LED test light does not blink: - Connect VAG1527B LED voltage tester between connector terminals 1
(B+) and 2.
- Start output Diagnostic Test Mode (DTM) for EVAP canister purge
regulator valve -N80- page 01
-51
.
LED must blink
- Connect VAG1598/22 test box to ECM harness connector page 01
-
67
.

If LED test light stays on: - Check wiring between connector terminal 2 and Motronic ECM terminal
15 for open circuit or short circuit to B+.
- Check wiring between connector terminal 2 and Motronic ECM terminal
15 for short circuit to Ground.
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24-124

Leak Detection Pump (LDP), checking


Note:
Component locations page 24
-1

Electrical testing

If resistance is NOT OK: - Disconnect harness connector for LDP -V144-.
- Connect multimeter US1119 (Fluke 83 or equivalent) and check
resistance at leak detection pump. Specified values:

Connector terminal 1 to terminal 3: 640-720

Connector terminal 2 to terminal 3: 11.0-21.0
- Replace leak detection pump -V144-.
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