fuel AUDI A4 1998 B5 / 1.G APB Engine Ignition System Checking

28-2

Safety precautions

To prevent injuries to persons and/or damage to
the fuel injection and ignition system, the
following must be noted:

WARNING!

Be alert when working on or near the engine.
High ignition secondary voltage can cause
serious personal injury and damage vehicle
components.

DO NOT touch or disconnect ignition wiring
when the engine is running or being turned
at starter speed.
DO NOT operate the starter if fuel injectors
are removed.
Always switch off the ignition before
connecting or disconnecting the battery,
otherwise the engine control module may be
damaged.
The ignition must be switched off before
connecting or disconnecting injection or
ignition system wiring or tester cables.
In order to run the engine at starting speed
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without actually starting it (e.g. to test
compression), disconnect the connectors
from the output stages of the ignition coils
and from all the fuel injectors. After
completing the work, check and erase the
DTC memory.
The ignition must always be switched off
when cleaning the engine.
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28-4
Technical data, ignition system

Engine code
APB
Engine idle RPM
Not adjustable - controlled by
Idle Air Control (IAC) 750 - 850 RPM
RPM limit

Operates by closing
throttle valve
Operates by shutting off
fuel injectors
approx. 6800 RPM
Ignition timing is determined
by the control module.
Ignition timing cannot be
adjusted.
Ignition system Single-coil system with 6 ignition coils located above spark plug connectors and installed
directly on spark plugs. The power output stages are located as separate components in air
cleaner housing.
Spark plugs connectors Resistance approx.: 2K Ohm
Firing order 1-4-3-6-2-5
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28-5

Ignition coils, checking


Note:
Misfiring is recognized by the On Board
Diagnostic (OBD). This means a non working
cylinder is stored with the cylinder number in the
DTC memory. This has an advantage in case of
a malfunction the trouble shooting procedure can
be started at a certain cylinder. Check the DTC
memory of the Engine Control Module (ECM)
before commencing trouble shooting.

Test conditions

No DTCs stored relating to any of the fuel
injectors
Determine a non working or misfiring cylinder as
follows:
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28-6

- With the engine running disconnect harness
connectors in sequence from fuel injectors, and
observe the engine performance.

or

- Compare spark plugs of all cylinders with each
other and check for soot on the electrodes.
When the faulty cylinder has been identified:

- Connect hand-held multimeter (resistance
measurement) to spark plug connector:

Note:
The spark plug connector can be disconnected
from the ignition coil.

Specified value: approx.: 2K Ohm.
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28-8
If malfunction remains at the same cylinder.

- Disconnect harness connector from ignition
coil.

Electrical Wiring Diagrams, Troubleshooting & Component Locations
If the Ground (GND) connection is OK. - Check Ground (GND) connection between socket 4a and engine
Ground (GND) for open circuit and short circuit to B+. - Repair any open/short circuit as necessary.
- Connect hand-held multimeter (voltage range) to terminal 15 of
harness connector and Ground (GND).
- Disconnect harness connector from fuel injector of cylinder to be
tested.
- Operate starter.
Specified value: approx. battery voltage
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28-11

Power output stages for ignition coils,
checking


Note:

Power Output Stage -N122 (black connector)
activates the ignition coils for cylinder bank 1
(cylinders 1 to 3).
Power Output Stage 2 -N192 (brown connector)
activates the ignition coils for cylinder bank 2
(cylinders 4 to 6).

Checking activation of power output stages

- Disconnect harness connectors from all six fuel
injectors.

Note:
It is important to ensure that no fuel is injected
during the test as this would damage the catalytic
converter. The harness connectors on the fuel
injectors must therefore be disconnected.
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28-34

Knock sensor control limit, checking

If the malfunction message "Knock control
regulation reached" is recorded in the DTC
memory the following tests must be carried out.
See also measuring value blocks 20, 21, 22, 23
and 24 Page 28
-35


Possible cause of malfunction
Corrective action
Malfunction
message relating to all cylinders
Poor fuel quality- Change to higher quality fuel (see Owner's
Manual)
or
malfunction
message relating to all cylinders in
one bank Incorrect tightening torque on
knock sensor - Loosen knock sensor, then tighten to 20
Nm (15 ft lb)
Knock sensor faulty- Check knock sensor Page 28
-41
.

Corrosion on connector
Loose components on engine- Secure loose components
Malfunction
message relating to one cylinder Mechanical engine damage- Check compression pressure
Loose components on engine- Secure loose components
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28-40
Evaluation display groups 20/21/22/23/24, - Ignition timing angle retard Indicated on display
Malfunction cause
Corrective action
All cylinders greater
than 12 KW
Knock sensor faulty- Check knock sensor Page 28
-41
.


Corroded connection

Knock sensor incorrect
tightening torque - Loosen and tighten knock sensor with 20 Nm (15 ft lb)

Components on engine
loose - Tighten components

Low fuel grade- Change fuel grade
One cylinder deviates
clearly from others Corroded connection- Check knock sensor Page 28
-41
.


Engine damage
Repair Manual, 2.7 Liter V6 5V BiTurbo Engine Mechanical, Engine
Code(s): APB, Repair Group 15, Cylinder head removing, check compression pressure
- Check compression pressure:


Components on engine
loose - Tighten components
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28-54
Evaluation display group 014, display field 3 Display field:
3
Possible cause
Corrective action
greater 15

Spark plug faulty
Spark plug connector faulty
Ignition coil or power output stage faulty- Check spark plug and ignition cable with
connector
- Check ignition coil Page 28
-5 .
- Check power output stages Page 28
-11


Fuel injector faulty
Check compression of one or more cylinder
weak - Check fuel injectors Page 24
-39
- Check compression pressure
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