1995 AUDI A4 check

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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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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21-10

Charge air pressure control (via load
signal), checking


WARNING!

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 .

Note:
If VAG1551 scan tool is not available, use
VAG1552 mobile scan tool instead.

- Unclip Data Link Connector (DLC) cover.

- Using VAG1551/3 adapter, connect VAG1551 Scan Tool (ST) or
VAG1552 mobile scan tool.
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21-14

Charge pressure leak test with VAG
1687


Intake system, checking for leaks using VAG
1687 Diagnostic Tool
Diagnostic trouble codes (DTCs) related to fuel
trim, charge pressure or mass air flow (MAF)
may be caused by:

Leaking (worn/torn) intake hoses during charge
conditions
Incorrectly torqued or improperly placed clamps
on intake hoses etc. causing leaks during
charge conditions

Check the charge air pressure system using the VAG 1687 Charge air
system tester.
Special tool VAG 1687 Charge air system tester preliminary set-up

- Back off pressure regulator knob -2- of VAG 1687 fully to protect gauge
when shop air supply is applied to assembly.
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21-25


CAUTION!
Part numbers are listed here for reference only.
Always check with your Parts department for
the latest information. 7 -
Bolt
20 Nm (15 ft lb)
8 -
Oil supply line Tightening torque for union nut: 25 Nm (18
ft lb) From oil filter bracket item - 1 -, page
Page 17
-6
9 -
Heat shield
10 -
Exhaust manifold
11 -
Bolt
Always replace35 Nm (26 ft lb)Coat thread and bolt head seating surface
with "G 052 112 A3" hot bolt paste.
12 -
Bolt 10 Nm (7 ft lb)
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