fuel pressure AUDI A6 1998 C5 / 2.G ATQ Engine Motronic Injection System Servicing Workshop Manual

24-2

It is possible that the control module will
recognize a malfunction and store a DTC during
some tests. After completing all tests and
repairs, DTC memory should therefore be
checked and erased if necessary. Readiness
code must be generated after DTC memory is
erased Page 01
-82
.

Always switch ignition off before cleaning
engine.
The battery should only be disconnected and
reconnected when the ignition is turned off,
since otherwise the Engine Control Module
(ECM) can be damaged.

WARNING!

Fuel system is under pressure! Place a cloth
around the connection point before opening
system. Then release pressure by carefully
loosening connection point.
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24-4
Technical data

Engine identification

ATQ (2.8 L / 5V/ 147 kW-engine)
Idle speed
Engine speed cannot be adjusted, it is regulated by idle
stabilization

720 to 820 RPM (front wheel drive)
630 to 730 RPM (all wheel drive)
Engine speed (RPM) limitation
via fuel injector shut-off
about 6800 RPM
Fuel pressure at idle speed Vacuum hose
connected
3.2 to 3.8 bar

Vacuum hose
disconnected
3.8 to 4.2 bar
Residual pressure after 10 min. cold engine about 2.2 bar positive pressure

warm engine about 3.0 bar positive pressure
Fuel injectors Injection stream Dual-hole nozzle / same for all
injectors

Injection quantity (30
s) 90 to 125 ml.

Resistance
(room temperature)
1)
13.5 to 15.5
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24-9


17 -
Engine Coolant Temperature (ECT) sensor
-G62-
for Engine Control Module (ECM)At coolant line behind cylinder head engine
bank 1 with Engine Coolant Temperature (ECT)
Sensor -G2- Checking Page 28
-23
If necessary, release pressure in cooling
system before removing
18 -
Throttle valve control module -J338- With throttle drive (power accelerator
actuation) -G186-, angle sensor -1- for
throttle drive (power accelerator actuation)
-G187-, and angle sensor -2- for throttle
drive (power accelerator actuation) -G188-
19 -
Intake Manifold Change-Over Valve -N156-
20 -
Fuel pressure regulator
21 -
Engine Speed (RPM) sensor -G28- in transmission housing via ring gearChecking Page 28
-19
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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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24-32

- 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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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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24-34

- Start engine and let run at idle.

The following malfunction are possible if the pressure does not drop:
Repair Manual, Fuel Supply System, Repair Group 20; Fuel supply
-
Front Wheel Drive or fuel supply
- All Wheel Drive

Note:
Pressure gauge displays the pressure behind the stopcock "intake
manifold side" after the stopcock is closed (in direction of fuel injector, fuel
pressure regulator). If the pressure drops in front of the stopcock (in
direction of fuel tank), the device cannot detect it. For this reason, the
center of this page states "If the pressure does not drop...". - Wait until pressure has dropped, and then switch off ignition.
Simultaneously close shut-off valve of VAG1318 pressure gauge (lever
perpendicular to direction of flow -arrow-).
There is a leak in the threaded connection between the pressure
gauge and the fuel supply line There is a leak at the supply line at fuel tank.There is a leak in the check valve in the Fuel Pump (FP).
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24-35
The following malfunctions are possible if the
pressure drops again:

Fuel pressure regulator faulty
Fuel injectors not properly sealed
Threaded connections of pressure gauge
behind stopcock is not properly sealed.

Note:
Close stopcock for removing the pressure gauge,
loosen threaded connection at VAG1318/15
adapter and let excess fuel escape into catch
reservoir by opening stopcock.
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