fuel pressure AUDI A4 1999 B5 / 1.G AEB ATW Engines Turbocharger System Workshop Manual

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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21-9

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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21-13
Diagnostic Trouble Codes (DTC) for charge air pressure regulation Diagnostic
Trouble Code
(DTC) VAG1397A Display
VAG1551 Display
Possible causes
Charge air
pressure too
low
Measured value below 1.37
bar (19.9 psi) (vehicles with
manual transmission)
Measured value below 1.30
bar (18.9 psi) (vehicles with
automatic transmission)
Current engine load
(display field 3) less than
specified engine load
(display field 2) Duty cycle (display field 4)
close to 99%
Wastegate bypass regulator valve
-N75- malfunctioning Wiring to wastegate bypass
regulator valve -N75-
malfunctioning Wastegate in turbocharger stuck
in open position Leak between turbocharger and
intake manifold Turbocharger malfunctioning
Charge air
pressure too
high
1)
Measured value above 1.47
bar (21.3 psi) (vehicles with
manual transmission)
Measured value above 1.40
bar (20.3 psi) (vehicles with
automatic transmission)
Current engine load
(display field 3) higher
than specified engine load
(display field 2) Duty cycle (display field 4)
close to 0%
Vacuum diaphragm for wastegate
malfunctioning Hoses to vacuum diaphragm (for
wastegate) over wastegate
bypass regulator valve -N75-
leaking Vacuum diaphragm wastegate in
turbocharger stuck in closed
position
1) If charge air pressure is too high, the fuel supply is shut off to protect the engine. The engine misfires at high engine
speeds.
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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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