Porsche 928 Workshop Manual page 593

24
Electronic Fuel Injection
928 S4
928 GT
Fault, Fault Code Possible Causes, Elimination, Remarks
c) Checking the hot wire slgnal (V)
Connect the plug to the air mass sensor. Take out LH relay XXV ent-
fernen and bridge terminals 67 and 30 at the base of the relay. Con-
nect terminals 6 and 7 at the LH control unit plug with a voltmeter.
Display: 2: 1.6 V
Blow on the hot wire in the air mass sensor and watch the voltmeter.
The voltage reading must change. (== 1.6 - 5 V)
d) Checking the hot wire burn-off circuit (visual check)
Run the engine with the air mass sensor installed and connected.
When an engine temperfture of > 60°C is reached, raise engine
speed above 2000 min
and then stiop the engine by switching off the ignition. After a delay
of approx. 4 seconds, the hot wire must glow for approx. 1 s (burn-
off function).
e) Emergency operating program
The emergency operating program stored in the LH control unit is ac-
tivated if the air mass sensor fails, so that the car can be driven to
the nearest authorized repair shop.
With engine warm and at engine speeds < 2000 min - ' = 3.5 ms ti
With engine warm and at engine speeds > 2000 min - ' I 6.3 ms ti
(ti = Injection time)
Test point 6
Idle speed control 01)
Fault code l-22
Call up actuator activation menu point
If no pulse is audible, check:
Power supply
Connect voltmeter to terminal 2 of disconnected idle
speed actuator plug and ground with the test leads.
Switch on the ignition.
Display: battery voltage.
No display:
Check power supply according to wiring diagram.
2
1
D24-16
LH-Diagnosis/Troubleshooting
Printed in Germsny - Xxv, ,990