Porsche 928 Workshop Manual page 601

24
Fuel System, Electronic Injection
928 S4
928 GT
Test point 17: Fuel pressure If there are hot starting problems:
The fuel collection pipe has a test connection
at the front right. Unscrew the cap nut of the
test connection.
Warning: the ball seal inside could fall out.
Connect a P 378 or VW 1318 pressure gauge
to the test connection. Start the engine and
run at idle speed with vacuum at the pressure
regulator.
Check with the engine stopped and the fuel
pump running, without vacuum at the pressure
regulator (to do this, remove the relay and
bridge terminals 87 and 30):
Test pressure 3.8 k 0.2 bar
- Switch off the fuel pump. Read ofl the pres-
sure value at the test pressure gauge (nomi-
nal value 3.8 + 0.2 bar).
Test pressure 3.3 + 0.2 bar
- Maximum permissible pressure drop with
engine warm: 0.5 bar In 30 minutes.
- If pressure drops below the specified value,
proceed as follows:
Build up pressure again by switching the fuel pump on briefly. Remove the return pipe at the pres
sure regulator )the fuel pump must not be switched on).
NO fuel escaping from the pressure
Fuel escaping frcxn the pressure regulator
Reconnect ret"r" hose
I
Build up pressure again
i
Disconnect rubber pressure hose
(tank to
pump)
in front 01 the fuel
pump
I I
Pressure drop Pressure drop
not okay
okay
I
I
Fault in fuel
Replace fuel
injectors pump holding
(leakage) valve
I
Check luel
injectors.
RZ+VX
leaking fuel
In,ectors.
Replace pressure re
End
D 24 - 24
LH-Diagnosis/Troubleshooting
Printed in Germany - XXV, 1990