Porsche 928 Workshop Manual page 599

24
Fuel System, Electronic Injection
928 S4
928 GT
If the pump does not run:
Check fuse No. 42 (38). If the fuse is in good
working order, remove the fuel pump relay and
conned terminals 87 and 30 at the base of the
relay. The fuel pump must then run.
If the pump runs, check the relay or activation
circuit. If the pump does not run, examine the
pipes and connections leading to the pump
and the pump itself.
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Test point 15: Engine speed signal
from EZK
Important: the EZK control unit plug must be
attached and the LH control unit plug
detached.
At the LH control unit plug, connect terminals
17 and 1 with the engine tester leads, using
the test leads.
Adjust the oscilloscope as stated by its manu-
facturer. Start the engine with the starter
motor. A control signal must be visible on the
oscilloscope.
Test point 16: Injector valves
Control system (V/Q)
If the engine can be run, pull off the injector
valve plugs one after the other. If the injector
valve is in good working order and combustion
in that cylinder is correct, engine speed will fall.
If the engine cannot be run, check:
a) Power supply
Pull off injection valve plug (to do this, first re-
move the
cover over the ring pipe). Remove LH relay
XXV and bridge terminals 87 and 30 at the
relay base. Connect voltmeter to the valve plug
contacts and ground, using the test leads.
Display: battery voltage
If no battery voltage is displayed, check the
current flow path according to the wiring dia-
gram.
b)Check injection valve coil resistances
Pull off the valve plugs. Use an ohmmeter at
the injection valve connection contacts to
measure the coil resistance.
Test value: approx. 18 Q
D 24 - 22
LH-Diagnosis/Troubleshooting
Printed in Germany - Xxv, 1990