Porsche 928 Workshop Manual page 619

Fuel System I Electronic Control
No display:
Disconnect the engine speed sensor plug con-
nection at the plug strip in the engine compart-
ment. Using test leads, connect the lead from
the tester to the center and outer plug contact
(terminals 1 and 2. pin side). Start the engine.
The sine wave pattern must be displayed on
the screen.
Engine speed sensor plug
Note
If connection 3 is grounded, the image must
not change.
If it changes, check sensor for continuity, cor-
rect gap and freedom from dirt.
Test point 14: ignition circuit
monitoring (refer to test point 10,
LH test plan)
If the exhaust gas temperature changes, for in-
stance on account of misfiring, the faulty injec-
tion circuit is shut down. The engine then runs
on 4 cylinders.
An ignition circuit monitoring relay at the
LH/EZK control unit controls this protective
device. 2 light-emitting diodes on the relay
housing show which injection circuit has been
shut down. For repairs, refer to 926 Repair Pro-
cedures, volume I-A, page 28-77.
Test point 15: Ignition system - output stages
Checking ignition timing
At idle speed
928 GT
675 + 25 l/min 10" bTDC f 2"
775 + 25 llmin
lVbTDCt2"
D 28 - 12
EZK-Diagnosis/Troubleshooting
Primed in Germany - xxv, ,990