1997 AUDI A4 APB Engine Ignition System Checking

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Ignition system, checking

General notes on ignition system


Always switch off the ignition before connecting
or disconnecting the battery, otherwise the
engine control module may be damaged.
The engine control module is equipped with On
Board Diagnostic (OBD).
For trouble-free operation of the electrical
components a voltage of at least 11.5 V is
necessary.
During some of the tests it is possible that the
control module will detect and record a
malfunction. The DTC memory must therefore
be checked and if necessary erased when all
tests and repair work have been completed.
After completing troubleshooting, repairs or
component tests, it is possible that the engine
will start, run for a short period and then cut out.
If this happens it may be that the immobilizer is
blocking the engine control module. In such
cases the DTC memory must be checked and if
necessary the control module must be adapted.
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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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CAUTION!

Before disconnecting the battery:

Stop the engine.
Be sure of proper radio code (for vehicles
equipped with coded anti-theft radio).

When connecting and disconnecting
electrical test equipment (LED voltage tester,
multi meter, etc.):
Be sure the ignition is switched OFF.
Use correct adapters from VAG1594
connector test kit
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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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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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- 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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If specification is not obtained:

- Replace spark plug connector.
If specification is obtained:

- Exchange spark plug from faulty (misfiring)
cylinder with one from another cylinder. Visually
check spark plug for damage e.g.: cracks on
ceramic body of spark plug.

- If malfunction (misfire) occurs now on other
cylinder, replace spark plug.
If the malfunction remains at the same cylinder:

- Exchange ignition coil from faulty (misfiring)
cylinder with one from another cylinder. Visually
check ignition coil for damage (ignition coil could
be cracked or bursted)

- If malfunction occurs now on other cylinder,
replace ignition coil.
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