AUDI A6 1996 C5 / 2.G ATQ Engine Motronic Injection System Servicing Owner's Guide

24-28

Notes:

Engine speed in display field 1 (actual engine
speed) is the current engine speed.
Engine speed in display field 2 (specified
engine speed) is a theoretical engine speed
calculated by the ECM.
At idle, the ECM always attempts to adapt the
engine speed (actual) to the specified engine
speed (specified).
This means that the engine speed (actual) must
always approximately match the engine speed
(specified) at idle.
Display fields 3 and 4 provide information, but
are not relevant for checking idle speed.
If specified value is obtained:

-
Press button.
Rapid data transfer
HELP
Select function XX

Indicated on display (function selection):
If specified value is not obtained:
- Check DTC memory again Page 01
-15
.
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- If DTC memory was erased, readiness code must be re-generated
Page 01
-82
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24-29

If idle speed is too high or low and there are
no DTCs in DTC memory, the following tests
(marked with dots) must be performed:

False air in intake air system, checking
Page 24
-64
.

Throttle valve control module, checking
Page 24
-141
.

Evaporative Emission (EVAP) canister purge
regulator valve always open, checking
Page 24
-128
.

Perform adaptation of throttle valve control
module Page 24
-142
.
Significance of 5 digit indication of display group 056 x
x
x
x
x
Display field 4
0 A/C compressor
0 = A/C compressor off
1 = A/C compressor on
0 Driving mode selected
0 = selector lever in P or N
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1 = selector lever in 2/3/4/D/R
0 A/C readiness maximum heating/cooling power
0 Indication always 0
0 Indication always 0
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24-30

Fuel pressure regulator and residual
pressure, checking


Note:
Fuel pressure regulator regulates fuel pressure
according to intake manifold pressure. This
ensures that the pressure drop at the fuel
injectors remains the same for each speed and
load range of the engine.

Special Tools and Equipment

Test requirements:
Repair Manual, Fuel Supply System, Repair Group 20; Fuel supply Front Wheel Drive or fuel supply
- All Wheel Drive

VAG 1318 with VAG 1318/7 adapter, VAG 1318/8 pressure hose with
connectors and VAG 1318/15 adapter Fuel Pump (FP) OK, checking Page 24
-49
.
Fuel Pump (FP) OK, checking: Fuel filter OK Battery voltage at least 12.7 V Vehicles with automatic transmission Selector lever in P or N.
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24-31

WARNING!

Fuel system is under pressure! Place a cloth
around the connection point before opening
system. Then release pressure by carefully
loosening connection point.

Checking system pressure - Remove engine cover (arrows).

Note:
If fuel should escape at the vacuum connection of the pressure regulator
during the following pressure test, replace pressure regulator. - Connect VAG1318 pressure gauge using adapters
VAG1318/7, /1318/8 pressure hose with connectors and 1318/15
adapter in supply line.
- Disconnect vacuum hose from pressure regulator to intake manifold at
pressure regulator and seal line.
- Start engine and let run at idle.
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- Measure fuel pressure.


Specification: 3.8 to 4.2 bar

- If the specified value is not reached, replace
pressure regulator on a trial basis and repeat
pressure test.

- If the specified value is not reached again, check
Fuel Pump (FP) or supply line for damage (e.g.
pinched areas) and replace if necessary.

- If the specified value is exceeded, check return
line for damage (e.g. pinched areas) and replace
if necessary.

Note:
During the following test, the engine must not run
for an unnecessarily long period of time with the
vacuum hose removed. Otherwise, the higher
fuel pressure can cause enrichment of the fuel to
air ratio, which under some circumstances can
cause the oxygen sensor control limits to be
exceeded, causing a DTC to be stored.

- Start engine and let run at idle.

-
Switch of electrical consumers (A/C system
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etc.).

- Connect vacuum hose at pressure regulator
while observing pressure drop at pressure
gauge.
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24-33

- Fuel pressure must drop by approx. 0.5 bar
when connecting the vacuum hose.

If the pressure change does not occur, the
following tests must be performed:


Check vacuum hose for tears and
damage.

Check vacuum hose at intake manifold for
throughput by disconnecting from pressure
regulator and blowing into it.

- If no leaks can be detected and if the vacuum
hose has throughput, replace the pressure
regulator.

Checking residual pressure

- Residual pressure 10 minutes after switching
engine off (minimum pressure).

Specified value with a cold engine: approx.
2.2 bar

Specified value with the engine at operating
temperature: approx. 3.0 bar
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Note:
Pressure increase for an engine at operating
temperature limited by the fuel expansion is
normal.
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