AUDI S4 1998 B5 / 1.G Engine Manual

Service.
For internal use only

198
All rights reserved. Subject
to change.
AUDI AG
Dept.I/GS-5
D-85045 Ingolstadt
Fax +49.841/89-6367
740.2810.17.20
Technical status: 01/98
Printed in Germany

The 2.7-litre V6 Biturbo
Design and Function
Self-study Programme 198

2
The 2.7-litre V6 biturbo .......
Turbocharged engines are already something
of a tradition at AUDI. The task now facing
AUDI’s engineers was to develop a worthy
successor to the 5-cylinder turbocharged
engine.
One of the key development goals for the
turbocharged engine was to achieve a good
level of dynamic response, particularly at the
bottom end of the rev band.
........ a further milestone in engine development by Audi!
The goal of AUDI’s engineers was to realise a
high “basic torque level“ and a torque
characteristic that rises in direct proportion to
engine speed to its peak.
The term “basic torque level“
describes the torque which is
immediately available when the
throttle is opened (e.g. at part
throttle or in overrun).
SSP 198/77

3
This Self-study Programme provides you with information
regarding design and function.
The Self-study Programme is not a Workshop Manual!
Please refer to the Service Literature for all the relevant
maintenance and repair instructions.
Page
Engine .........................................................
Technical data, crankshaft, cylinder head,
camshaft timing, cooling circuit, engine
lubrication, overview of components, air ducting,
charging, exhaust system, pneumatically
controlled systems, charge pressure control, air
divert control in overrun, ACF system, crankcase
breather
4
Motronic ME 7.1 ..........................................
Subfunctions, system overview
31
Subsystems of the Motronic .....................
Torque-oriented engine management, torque-
oriented functional structure, Electronic throttle,
exhaust gas temperature control
33
Sensors .......................................................
Additional sensors of the Motronic
49
Auxiliary signals/interfaces ...................... 57
Functional diagram ..................................... 62
Self-diagnosis .............................................
Vehicle diagnosis, test and information system
VAS 5051, test box V.A.G 1598/31
64
Transmission ..............................................
Self-adjusting clutch, gearbox
66
Contents
Important!/Note!
New!

4
Engine
The 2.7-litre V6 biturbo
This engine will also be used in the Audi S4
and Audi A6.
The engine used in the A6 has a comfort-
oriented setup, which means that it has
different torque and power output.
This effect was principally achieved by
modifying the software configuration of the
engine control unit.A tuning protective device prevents
the S4 engine control unit being
installed in the A6!
This prevents misuse, which can
result in damage to the drivetrain!
An auxiliary heater is not available
as an option for the S4 and the A6,
due to the constraints on space.
BITURBO
SSP 198/01

5
The technical data
•
Configuration:
V6 engine with 90° V-angle and twin
turbochargers
•
Engine code:
S4: AGB
A6: AJK
•
Output:
S4: 195 kW at 5800 rpm
A6: 169 kW at 5800 rpm
•
Torque:
S4: 400 Nm at 1850 to 3600 rpm
A6: 310 Nm at 1700 to 4600 rpm
•
Maximum speed:
6800 rpm
•
Compression ratio:
9.3 : 1
•
Displacement:
2671 cm
3

•
Bore:
81 mm
•
Stroke:
86.4 mm
•
Weight:
approx. 200 kg
•
Engine management:
Motronic ME 7.1
•
Firing order:
1-4-3-6-2-5
•
Fuel type:
S4: 98/95/91 RON
A6: 95/91 RON
•
Compliant with emission standard:
EU III-DFigures obtained using 98 RON
unleaded premium fuel to
89/491/EEC.
Figures obtained using 95 RON
unleaded premium fuel to
89/491/EEC.
500
450
400
350
300
250
200
150
100
50
0200,0
180,0
160,0
140,0
120,0
100,0
80,0
60,0
40,0
20,0
0,0
0 1000 2000 3000 4000 5000 6000 7000
SSP 198/02

Speed [rpm]
Torque [Nm]Output [kW]

S4
500
450
400
350
300
250
200
150
100
50
0180,0
160,0
140,0
120,0
100,0
80,0
60,0
40,0
20,0
0,0
0 1000 2000 3000 4000 5000 6000 7000
SSP 198/46

Speed [rpm]
Torque [Nm]Output [kW]

A6

6
Engine
The crankshaft
The crankshaft is identical to that used in the
2.8-litre V6 engine.
The crankshaft bearing caps are attached to
the central crankcase by 4 bolts.
•
The 4-bolt connection reduces the load on
the bearing caps considerably.
The middle two crankshaft bearing caps are
also bolted to the side of the crankcase.
•
The lateral bolted connection helps to
improve acoustics.The pistons are forged to enable them to
withstand the high loads to which they are
subjected.
Due to the high combustion pressures, a 2-
material bearing shell is installed on the
connecting rod side. The bearing cap has a 3-
material bearing shell.
Advantage:
The bearing shell has a high load-bearing
capacity
SSP 198/11

Lateral bolted connection
4-bolt connection
2-material
bearing shell
3-material
bearing shell

7
Cylinder head
The cylinder heads are largely identical to
those used in the V6 naturally aspirated
engine. Common parts are used for both banks
of cylinders.
The mounting position of the right-hand
cylinder head is rotated through an angle of
180° in relation to the left-hand cylinder head.
The timing of the inlet camshafts is engine-
dependent.
To improve heat dissipation, the exhaust
valves are sodium-filled.The shape of the inlet duct causes the drawn-
in air to tumble.
Advantages:
•
A good degree of swirl and high ignitability
fuel-air mixture are achieved
•
The tumble effect allows more efficient
combustion
For a turbocharged engine, the compression
ratio of 9.3 : 1 is high.
Advantage:
•
High ”basic torque level“ and fuel
economy
Tumble duct
In combination with five-valve-
per-cylinder technology, the inlet
duct is shaped as a so-called
“tumble duct“.
Tumble duct
Tumble effect

SSP 198/78

8
Engine
The variable valve timing
The camshaft timing has been modified
compared to the 2.8-litre V6 engine to meet the
demands of turbocharging technology.
Variable valve timing with an adjustment angle
of 22° is used here for the first time in
turbocharged engines
.
Advantage:
•
A torque increase of approx. 10% is
achieved at the bottom and top ends of the
engine speed range.
•
Better emission levels and fuel
consumption figures.
The variable valve timing is activated by the
Motronic by means of camshaft adjustment
valves N205 and N208.The design and function of the
variable valve timing are already
described in Self-study Programmes
182 and 192.
Activation of the variable valve timing is
dependent on engine load and speed.
In the self-diagnosis, you can find out whether
the variable valve timing is active or not by
reading out the relevant measured value block
(refer to Workshop Manual).
0
0 1000 2000 3000 4000 5000 6000 7000
SSP 198/45

Diagram of variable valve timing
(shown using the 265 bhp engine as an
example)
Engine speed
Engine load in %
Variable valve timing active
= advance position
Full throttle

9
SSP 198/03

Cooling circuit
Both exhaust gas turbochargers are water-
cooled and integrated in the cooling circuit.
When the coolant thermostat is closed, the
coolant flows back to the coolant pump along
the short-circuit line as well as the heat
exchanger.
When the coolant thermostat is open, the
coolant flows back to the coolant thermostat
through the radiator (primary flow) or through
the oil cooler and expansion tank (secondary
flow).Located in the cooling circuit is a electrical
coolant pump.
This pump is required as a means of
protection against overheating of the coolant
under high thermal load, e.g. when the hot
engine is turned off.
Short-circuit
line
Continued coolant function pump
Heat exchanger
Coolant
Expansion
tank
Radiator fan thermoswitch F18/F54
Oil cooler
Radiator
Thermoswitch for F95
Coolant temperature
senders G2 and G62
Coolant pump

10
SSP 198/10

Engine
Electrical coolant circulation pump V51
Electrical coolant circulation pump V51 is
located in the engine’s V angle.
If the coolant temperature is too high,
thermoswitch for coolant circulation run-on
F95 activates the additional coolant function.
The high temperatures which occur at the
exhaust gas turbocharger produce vapour
bubbles which prevent coolant being drawn in
by pump V51.
When pump V51 starts up, the coolant flows
through the exhaust gas turbocharger and the
cylinder heads. The direction of flow in the
turbocharger cooling circuit is reversed by
this.Due to this reversal of the direction of coolant
flow, coolant is drawn in via the cylinder heads
(large cross-sections), which means that any
vapour bubbles which develop are expelled
from the exhaust gas turbocharger lines.
The electrical coolant circulation pump again
draws in coolant along the rear coolant pipe,
thereby recirculating the coolant.
Rear coolant pipe
Electrical
coolant
circulation pump
V51
Thermoswitch for additional coolant
function F95
Radiator fan thermoswitch
F18/F54