Operating Modes - Audi 4.2-litre V8 FSI Service Training

Communications between control units
in the RS4
The engine control unit (master) J623 computes
and controls the signals from the actuators for
cylinder bank 1.
Most sensors are connected to the engine control
unit (refer to System overview, pages 38/39).
Both control units are connected to the CAN data
bus; the slave control unit is used as a receiver only.
The load signals required to compute and control
the signals for the actuators of cylinder bank 2 are
transmitted via private bus.
The slave control unit acts as the misfire detector
for each of the eight cylinders. It also processes the
signal from the engine speed sender G28.
Control unit 1 - master

Operating modes

Start - high-pressure stratified charge start
Injection of the metered fuel mass begins during
the compression stroke phase and ends shortly
before the firing point.
After start - HOSP = homogeneous split
Application:
– Heating the primary catalytic converters to
300 °C in approx. 12 sec.; lambda value 1.05
– Intake manifold flap position: closed
– Throttle valve position: wide open
Injection:
– First injection approx. 300° before ignition TDC
– Second injection of small amount of fuel approx.
60° before ignition TDC, retarded ignition timing
Master and slave control units are identical in
design and have the same part number.
A voltage code in the control unit determines
whether the control unit in the master or the slave.
If battery positive is applied to the encoding pin, the
control unit is the master.
Private bus
In comparison to the low-pressure start system,
homogenisation is greatly improved by utilising the
heat of compression for carburetion, and HC emis-
sions are reduced.
– Mixture combusts very late
– Exhaust valve already open
As a result, the cat reaches its operating tempera-
ture very quickly.
Normal operation homogeneous carburetion
(lambda 1) with open or closed intake manifold flap
(map based)
Control unit 2 - slave
CAN data bus
377_064
41