fuel AUDI A8 1998 D2 / 1.G ATQ Engine Motronic Injection System Servicing User Guide
[x] Cancel search | Manufacturer: AUDI, Model Year: 1998, Model line: A8, Model: AUDI A8 1998 D2 / 1.GPages: 78, PDF Size: 1 MB
Page 35 of 78
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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
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.
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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Page 36 of 78
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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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Page 37 of 78
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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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Page 39 of 78
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- 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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Page 40 of 78
Note:
Pressure increase for an engine at operating
temperature limited by the fuel expansion is
normal.
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Page 41 of 78
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- 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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Page 42 of 78
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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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Page 43 of 78
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Fuel injectors, checking
Special Tools and Equipment
VAG1526A
VAG1527B
VAG1594A
VAG1598/31
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Page 44 of 78
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Checking internal resistance
- Remove engine cover (arrows).
- Disconnect harness connector at the fuel injector to be tested.
With an engine at operating temperature, the resistance increases by
approx. 4 to 6 .
If specified value is not obtained: - Connect multimeter at valve for resistance measurement.
Specification: 13.5 to 15.5
- Replace fuel injector Page 24
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.
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Page 45 of 78
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Checking voltage supply
Test requirements:
Fuel Pump (FP) OK, checking Page 24
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49
.
Fuse for fuel injectors OK
Electrical Wiring Diagrams, Troubleshooting &
Component Locations binder
- Disconnect harness connector at the fuel
injector to be tested.
If LED does not light up: - Connect VAG1527B voltage tester as follows:Harness connector
Terminal
Measure to
1 Engine Ground (GND)
- Switch ignition on.
LED must light up.
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