Porsche 928 Workshop Manual page 621

28
Fuel System I Electronic Control
928 s4
928 GT
To display the ignition pattern for ignition cir-
cuit II (left side), connect the tester to the igni-
tion lead for cylinder 5 and the front left coil.
5
8
3 2
5
Cylinders:
Note:
If a fault is indicated for all cylinders, it must be
in the primary or secondary current circuit
from the coil to the distributor rotor,
If the fault is indicated for one cylinder only, it
must be located after the distributor rotor.
b) Resistances at coil, high-
tension distributor and spark plug
caps
Coil (Q/V):
Primary resistance
Terminals 1 + 15
0.4 - 0.7 R
Secondary resistance
Terminals 1 + 4
5 - 8.7 kQ
Voltage at
terminal 15 with
engine running
>lOV
High-tension distributor (a):
Distributor rotor
Suppression resistor 1 kQ
Inspect for damage, tracking or oxidation.
Spark plug caps (0)
Suppression resistor 3 kQ
Inspect for damage, tracking or oxidation.
c) Activating the high-tension side
To speed up troubleshooting in the ignition sys-
tem, the ignitrion trigger signal can be simu-
lated. To do this, disconnect the 2-pin connec-
tor (arrow) above the ZEL (green/white lead).
Connect plug pins with test leads.
Connect oscilloscope tester lead terminal 4 to
ignition lead terminal 4.
Switch on the ignition. If 12 V is applied at inter-
vals to one of the two plug pins with the test
lead, a high-tension peak should be visible
each time on the oscilloscope screen (ignition
trigger).
- If no signal is visible, check:
- Power supply to output stage and coil.
- Ground point for output stages (under
right-hand coil).
- Plug connections at output stages, coils
and high-tension distributor.
- The high-tension components (e.g. coil, ig-
nition leads, spark plug caps . ..)
- Wiring continuity from control unft plug to
output stage (green lead: ignition lead I,
white lead: ignition lead II).
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D28-14
EZK-DiagnosisiTroubleshooting
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