Intake AUDI A4 1999 B5 / 1.G EVAP Workshop Manual

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EVAP system leak detection


Function of leak detection system
The leak detection system can recognize leaks in
the entire fuel system, including the main fuel
tank, the EVAP canister and EVAP canister
purge regulator valve -N80.
On the mechanical side, the leak detection
system consists of a vacuum-operated
diaphragm pump (LDP) with a reed contact on
the pump diaphragm rod. The pump receives
vacuum from the intake manifold.

If the leak detection system is triggered; the
diaphragm pump pressurizes the fuel system
between 20 and 30 mbar.
If specified pressure is reached, the pump
diaphragm remains extended and the reed
contact remains in the "open" position.
If the pressure drops (i.e. there is a leak), the
diaphragm moves back and the reed contact
closes.
During diagnosis, first there is a measurement
of whether the reed contact has closed within
10 seconds. If this does NOT occur, the tank
system is then sealed.
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Checking LDP via Read Measuring Value
Block (vehicles with mechanical throttle
control)

Note:

Always replace O-rings, sealing rings and
gaskets.
Radiator fan must not come on during the
test!

Troubleshooting requirements
DTC memory checked and no DTCs stored
All electrical consumers switched OFF
A/C switched OFF
Intake Air Temperature lower than 90 C
Display group 004, channel 4.

Engine Coolant Temperature less than 95
C Display group 004, channel 3.

Throttle angle less than 10 % Display
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Note:
Fuel system pressurization depends on volume of fuel system and
amount of fuel in tank.
If fuel system pressurization does not stabilize:
CAUTION!
Clamp only soft rubber lines when isolating a leak. To avoid risk of
damage, never clamp hard plastic lines!
Note:
Any flow shown on flow meter indicates a leak. Flow before flow meter
flag set at vehicle leak standard may indicate a sporadic DTC.
If flow meter on tester registers flow near or above preset pressure: - Attach fuel cap adapter to filler neck (arrow) and test hose to adapter.
- Turn control valve from "Hold" to "Test".
- Allow fuel system to pressurize.
- Verify all fuel system outlets have been sealed before continuing.

- Clamp off hose (arrow) leading from EVAP purge regulator valve -N80-
to intake manifold (pictured: AHA engine in A6).
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EVAP system leak detection circuit,
schematic diagram (vehicles with 2.7 ltr.
turbo engine)

Repair Manual, 2.7 Liter V6 5V BiTurbo Fuel
Injection & Ignition, Engine Code(s): APB, Repair Group 24
1 -
To air intake before both turbo chargers
2 -
Check valve Installation position: Arrow at housing
indicates flow-through direction.
3 -
Evaporative Emission (EVAP) canister
purge regulator valve -N80- Location: On right side of engine
compartment Checking:
4 -
Vent line
From EVAP canister to EVAP canister
purge valve regulator valve -N80 Installation position: On right side on
vehicle under-side. Attached to fuel tank.
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11 -
Vacuum reservoir
For Leak Detection Pump (LDP) -V144-Location: in left front wheel well
12 -
Check valve Installation position: Arrow at housing
indicates flow-through direction.
13 -
To intake manifold at top rear
14 -
To intake manifold at top
15 -
Check valve Installation position: Arrow at housing
indicates flow-through direction.
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pair&id=AUDI.B5.GE04.20.5