1998 AUDI S4 Turbo

28
SSP 198/05

Engine
Divert air control in overrun
To avoid pumping the exhaust gas
turbochargers when a sudden transition from
high load to overrun is made, two divert air
valves are used.
The Motronic also activates the
two pneumatic divert air valves by
means of
an
electrical changeover
valve, the divert air valve for
turbocharger N249.
Advantage:
•
Controlled opening of the
divert air valves reduces the
noise level in the induction
tract and reduces fuel
consumption.
The divert air valve N249, in combination with
the vacuum reservoir, enables the divert air
valves to operate independently of the intake
manifold pressure.
The system is designed in such a way that the
pneumatic divert air valves continue to be
opened by the intake manifold pressure if the
electrically actuated divert air valve N249 fails.
Divert air valve for turbocharger N249
Vacuum reservoir (inside
wheelhousing on the left)
Divert air valve (pneumatic)
with flow
without flow
Non-return valve

29
SSP 198/06

Vacuum in intake manifold:
Non-return valve 1 open. Fuel vapours return
to intake manifold.
charge pressure in intake manifold:
Non-return valve 2 open. Fuel vapours return
upstream of exhaust gas turbocharger.
ACF system
Integrated in the lines of the ACF systems are
the solenoid valve for activated charcoal
canister N80 and two non-return valves.
The engine control unit, assisted by solenoid
valve N80, regulates the return rate of the fuel
vapours from the ACF canister.
The Motronic operates the solenoid valve
cyclically using a pulse duty cycle.
The non-return valves control the return of fuel
vapours, depending on operating state.
ACF canister
Solenoid valve for activa-
ted charcoal canister N80
Non-return valve 2Non-return valve 1
Vacuum in intake manifold
Charge pressure in intake manifold

For the exact line routing, please refer
to the Workshop Manual.

32
Actuators
Heater for lambda probe
(bank 1) Z19 and (bank 2) Z28
Divert air valve for turbochargers
Camshaft adjustment valve
(bank 1) N205 and (bank 2) N208
Throttle valve control part J338
with throttle valve drive G186
Solenoid valve for
charge pressure control N75
Solenoid valve for activated charcoal
canister N80
Output stage (bank 1) N122 and
ignition coils N (cyl. 1), N128 (cyl. 2)
and N158 (cyl. 3)Injectors (bank 1) N30, N31, N32
Fuel pump relay J17 and
fuel pump G6
Output stage 2 (bank 2) N192 and
ignition coils N163 (cyl. 4), N164 (cyl. 5)
and N189 (cyl. 6)
Fault lamp for electric
throttle control K132
Auxiliary signals

Sensors
Engine speed sender G28
Hall senders (bank 2) G40 and (bank 1)
G163
Lambda probes (bank 1) G39 and (bank 2) G108
Throttle valve control part J338
with angle sender (1) G187 and (2) G188 for
throttle valve drive G186
Intake air temperature sender G42
Coolant temperature senders G2 and G62
Charge pressure sender G31
Knock sensors (bank 1) G61 and (bank 2) G66Accelerator position sender G79 and 2 G185Exhaust gas temperature senders (bank 1)
G235 and (bank 2) G236Brake light switch F and brake pedal
switch F 47
Clutch pedal switch F36
Auxiliary signals

SSP 198/14
EPC

Injectors (bank 2) N33, N83, N84
Hot-film air mass meter G70
Control unit for Motronic J220

Altitude sender F96 is
integrated in the engine
control unit.
Diagnosis
Motronic ME 7.1

46
SSP 198/26

Subsystems of the Motronic
Exhaust gas temperature control
A new feature of Audi automobiles
is a function which monitors
exhaust gas temperature over the
entire engine speed range.
For turbocharged engines, the maximum
permissible exhaust gas temperature is a key
design criterion.
To protect the exhaust gas turbocharger and
the exhaust manifold, the exhaust gas
temperature should not exceed 1000 °C for a
lengthy period of time.
Since many of the components which
influence the exhaust gas temperature have
tolerances, thermodynamic adaptation
previously took place at 950 °C for safety’s
sake.
This was achieved by enriching the air/fuel
mixture.
The exhaust gas temperature is recorded in a
cylinder-bank-specific manner by the two
exhaust gas temperature senders G235 and
G236.
The Motronic controls the exhaust gas
temperature to 980 °C by enriching the air/fuel
mixture .
It is therefore possible to largely dispense with
the prophylactic enrichment process that has
been standard practice until now.
The mixture is only enriched...
... when necessary and
... to the extent necessary.
This means that engine operation with lambda
= 1 is possible up to high load and engine
speed ranges.
Advantage:

• Improved efficiency and reduction of fuel
consumption as well as exhaust emissions.
Exhaust gas temperature sender
Engine control unit
Injectors
G235
G236

47
SSP/198/13

Exhaust gas temperature sender
G235 and G236
To facilitate exhaust gas temperature control,
the exhaust gas temperature must be recorded
to a high degree of accuracy.
An accuracy of ± 5 °C is achieved in the
measurement range from 950 °C to 1025 °C.
The exhaust gas temperature sender is located
inside the exhaust manifold upstream of the
exhaust gas turbocharger.
It comprises a measuring sensor and
evaluation electronics.
The measuring sensor and the control unit are
permanently connected by means of a
shielded, heat-resistant wire.
The evaluation electronics convert the signal
which the measuring sensor generates into a
pulse-width-modulated signal (PWM signal).
This is a square-wave signal with a fixed
frequency and a variable pulse duty factor.
The pulse duty factor is expressed as a
percentage . The measurement range extends
from
³
10% to
£
90%.
A specific pulse duty factor is assigned to each
temperature (refer to diagram).
Substitute function and self-diagnosis:
A pulse duty factor of <1% or >99% is
recognised as a fault.
A fault is detected as of a certain enrichment
quantity.
If a sender fails, the charge pressure is reduced
to a safe level and an emergency enrichment
characteristic (engine speed-dependent) is
used.
Exhaust gas temperature sender
evaluation electronics
SSP 198/56
90%
70%
50%
30%
10%
945°C
950°C
960°C
970°C
980°C
990°C
1000°C
1010°C
1025°C
1030°C
Exhaust gas temperature
Pulse duty factor
Meas.

49
Sensors
Charge pressure sender G31
The charge pressure sender is located
upstream of the throttle valve control part.
The Motronic supplies the sender with a
voltage of 5 volts and earth.
The signal which the sender generates is a
pressure- proportional voltage ranging from 0
to 5 volts.
At atmospheric pressure (at sea-level), the
voltage is approx. 2.5 volts.
The signal is used for charge pressure control.
The Motronic also needs information on
charge pressure so that it can take counter-
measures if the maximum permissible
pressure is exceeded.
Substitute function and self-diagnosis:
If sender G31 fails, the charge pressure is
controlled via the characteristic curve (engine
speed-dependent). This will result in a
deficiency of engine power.
SSP 198/29
Charge pressure sender G31
The altitude sender F96 ....
... is integrated in the engine control unit, as is
normally the case with turbocharged engines.
... is required to control the charge pressure. In
conditions of decreasing air pressure (lower
density), the charge pressure is reduced to
prevent the turbocharger overspeeding.
... influences the air/fuel mixture composition
at engine start-up. The starting mixture is
leaned down with rising altitude.Substitute function and self-diagnosis
If a signal fails, the charge pressure is reduced
to a safe level, which results in a deficiency of
engine power.
Adaption of the injection quantity at start-up
no longer takes place.
The fault message “Control unit defective“ is
displayed in the self-diagnosis.
The following chapter presents the new features of the sensors, provided that they have not
already been described in the chapter on Subsystems of Motronic.

52
Sensors
Lambda probes G39 and G108
The planar lambda probe is a further
development of the finger-type lambda probe
and has a transient response at lambda = 1.
There is a single lambda probe in the exhaust
pipe running to each of the primary catalytic
converters.
To ensure that the exhaust gases are treated
efficiently, it is important that the lambda
probe should react quickly. The lambda probe
should therefore reach its operating
temperature within as short a space of time as
possible. Its planar (= flat, elongated) design
makes this possible.
The probe heater is integrated in the sensor
element. It quickly reaches its operating
temperature despite its lower heating capacity.
Note:
At an exhaust gas temperature as low as 150
°C, the probe heater generates the necessary
minimum temperature of 350 °C.
The lambda control is ready to operate approx.
10 seconds after engine start-up.
A porous, ceramic protective layer is sintered
onto the sensor element.
This layer prevents the sensor element being
damaged by residues in the exhaust gas.
It ensures that the sensor element will have a
long service life and meet the tough functional
demands.
Substitute function:
Controlled operation based on a characteristic
curve (cylinder bank-specific).A new generation of probes used in
the biturbo for stereo lambda
control.
Advantages:
• The warm-up period is short, which means
lower emissions during the warm-up phase
• Low heating power consumption
• More stable control characteristic
SSP 198/37
Section
Probe heater
Sensor element

62
Functional diagram
Components:
F Brake light switch
F36 Clutch pedal switch
F47 Brake pedal switch
F96 Altitude sender (integrated in engine
control unit)
G2 Coolant temperature sender
G6 Fuel pump
G28 Engine speed sender
G31 Charge pressure sender
G39 Lambda probe (cylinder bank 1)
G40 Hall sender (cylinder bank 2)
G42 Intake air temperature sender
G 61 Knock sensor (cylinder bank 1)
G62 Coolant temperature sender
G66 Knock sensor (cylinder bank 2)
G70 Air mass meter
G79 Accelerator position sender 1
G108 Lambda probe (cylinder bank 2)
G163 Hall sender (cylinder bank 1)
G185 Accelerator position sender 2
G186 Throttle valve drive (electric throttle
control)
G187 Angle sender 1 for throttle valve drive
G188 Angle sender 2 for throttle valve drive
G235 Sender 1 for exhaust gas temperature
G236 Sender 2 for exhaust gas temperature
J17 Fuel pump relay
J220 Motronic control unit
J338 throttle valve control part
K132 Warning lamp for electric throttle
control
N Ignition coil, cylinder 1
N30 Injector, cylinder 1
N31 Injector, cylinder 2
N32 Injector, cylinder 3
N33 Injector , cylinder 4
N75 Solenoid valve for charge pressure
control
N80 Solenoid valve for activated charcoal
canister
N83 Injector, cylinder 5
N84 Injector, cylinder 6
N122 Output stage (cylinder bank 1)
N128 Ignition coil, cylinder 2
N158 Ignition coil, cylinder 3
N163 Ignition coil, cylinder 4
N164 Ignition coil, cylinder 5N189 Ignition coil, cylinder 6
N192 Output stage (cylinder bank 2)
N205 Camshaft adjustment valve 1 (cylinder
bank 1)
N208 Camshaft adjustment valve 2
(cylinder bank 2)
N249 Divert air valve for turbocharger
Z19 Heater for lambda probe
Z28 Heater for lambda probe 2
I To dash panel insert
II To dash panel insert (warning lamp)
Additional signals
1 CAN-high (automatic gearbox)
2 CAN-low (automatic gearbox)
3 „Set/decelerate“ signal for cruise
control system
4 “Off“ signal without cancellation for
cruise control system
5 “On/Off“ signal with cancellation for
cruise control system
6 Resume/accelerate“ signal for cruise
control system
7 Road speed signal
8 Immobiliser/diagnosis signal
9 Air conditioner compressor “On/Off“
signal
10 Coolant temperature signal
11 Engine speed signal
12 Fuel consumption signal
Colour codes:
Input signal
Output signal
Positive
Earth
Bidirectional