AUDI TT 1996 8N / 1.G AEB ATW Engines Turbocharger System Workshop Manual

21-1


Turbocharger system

Note:

Observe rules of cleanliness Page 21
-22
.

Charge air pressure control connection diagram
Page 21
-2 .

All hose connections are secured with hose
clamps:

parts catalog.

charge air pressure system must be free of
leaks.
Replace self-locking nuts.
Always replace gaskets.
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21-2


Charge air pressure control, system
overview

Vehicles with manual transmission
1 -
PCV valve
For crankcase ventilation
2 -
Evaporative Emission (EVAP) canister
purge regulator valve -N80-
3 -
To Evaporative Emission (EVAP) canister
4 -
Check valve for Evaporative Emission
(EVAP) canister Installed position (light/dark): as shown in
illustration
5 -
Turbocharger
6 -
Fuel pressure regulator
7 -
Intake manifold
8 -
To Leak Detection Pump (LDP) -V144-
9 -
Crankcase ventilation
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21-3


10 -
Check valve for Evaporative Emission
(EVAP) canister
Installed position (light/dark): as shown in
illustration
11 -
Charge air cooler
12 -
Vacuum diaphragm For wastegate
13 -
Charge pressure bypass valve Checking Page 21
-4
14 -
Wastegate bypass regulator valve -N75-
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21-4

Charge pressure bypass valve, checking


Note:

The charge pressure bypass valve is located in
front of the turbocharger. It is opened by
vacuum during deceleration and when under
partial load at idle. This reduces charge air
pressure in front of the throttle valve and keeps
the turbocharger spinning at higher RPMs.
Check the charge pressure bypass valve if
experiencing reduced performance or turbo lag.

Special tools and equipment
VAG1390 hand vacuum pump

If valve does not open/close or valve plate does not seal correctly when
valve is closed: - Connect VAG1390 hand vacuum pump to vacuum connection on
recirculation valve.
- Operate hand vacuum pump.
Recirculation valve must open (arrow).
- After approx. 30 seconds, operate vent valve on hand vacuum pump.
Recirculation valve must close (arrow).
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- Replace valve and secure recirculation shut-off valve connections
using hose clamps.
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21-5

Turbocharger and wastegate, checking

If special testing equipment is required during
test drive, heed the following WARNING:

WARNING!

When driving or riding in an airbag-equipped
vehicle, NEVER hold the scan tool or other
test equipment in your hands or lap while in
motion. Objects between you and the airbag
increase the risk of injury in an accident.
During a test drive in an airbag-equipped
vehicle, test equipment must always be
fastened to and operated from the rear seat
by a second technician.

Special tools and equipment
VAG1397A turbocharger tester
VAG1551 scan tool with VAG1551/3 adapter
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21-6

Test conditions:

Check DTC memory Repair Manual, 1.8
Liter 4-Cyl. 5V Turbo Fuel Injection &
Ignition, Repair Group 01
Perform output diagnostic test mode
(function 03)
Minimum engine oil temperature: 60 C
(140 F)

All vacuum connections are free of leaks

Test procedure

- Using T-fitting, connect VAG1397A turbocharger tester test hose to
front of intake manifold.
- Guide test hose over rear corner of hood through right window opening
into vehicle interior.
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21-7


Note:
WARNING! - Turn turbocharger tester on and select measuring range -I- (absolute
pressure).
- Connect test hose to connection flange -I-.
Hoses must be connected so there is no possibility of leaks, otherwise
incorrect readings may result. Ensure test hose is not pinched at the hood and/or window.By pressing the memory button "M" on the turbocharger tester, the last
test value is stored until either memory button "M" is pressed again or
the turbocharger tester is shut off. A blinking comma in the display field indicates a value has been
stored. An arrow appears in the top left corner of the display field if the
turbocharger tester battery voltage drops below the allowed
specification. Before testing, drive vehicle briskly for at least 3 km (approx. 2 miles)
without frequent stops. Always use a second technician to take measurements via the
VAG1397A turbocharger tester when test-driving vehicle for this
test. Follow "WARNING!" Page 21
-5 .
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21-8

Vehicles with manual transmission:

- Accelerate vehicle in 3rd gear at full throttle from
2000 RPM and watch tachometer.

Vehicles with automatic transmission: - At 3000 RPM press memory button "M" on turbocharger tester.
Specification: 1.37-1.47 bar (19.865-21.315 psi)
- Drive with selector lever in range 2.
- Accelerate to 3000 RPM and wait for transmission to shift into 2nd
gear.
- Press accelerator pedal to kickdown position (transmission will not shift
down at this vehicle/engine speed).
- At 4500 RPM, press memory button "M" on turbocharger tester.
Specification: 1.3-1.4 bar (18.85-20.30 psi)
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21-9

Note:
For vehicles with automatic transmission the
charge air pressure test may not always provide
a definitive reading of proper charge air pressure
regulation. If pressure readings are at the lower
end of the specified range, measure charge air
pressure control via load signal Page 21
-10
.

All vehicles:
If measured value is above or below specification
Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 24.

Note:
If no charge air exists and a rumbling sound is
heard from the engine compartment, the causes
are as follows:

Charge pressure bypass valve
malfunctioning.
Vacuum line to charge pressure bypass valve
leaking or disconnected.
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