Porsche 928 Workshop Manual page 595

24
Electronic Fuel Injection
928 S4
928 GT
Fault, Fault Code
Test point 8
Oxygen regulator
Control (lean)
Fault code l-24
Possible Causes, Elimination, Remarks
Mixture preparation problems are preventing the oxygen regulator
from operating within its control range. It therefore moves back to its
stop.
Test 1: With the engine running and a CO tester connected,
note the CO content (between 0.4-l .2 %)
Too rich: Check fuel pressure (test point 17)
Check injector valves for leaks
Test point 9
Oxygen sensor
Open circuit
Fault code l-25
a) Checking sensor signal (V)
Disconnect the oxygen sensor plug close to the central electrics.
Connect voltmeter at the sensor end to the single plug pin and
ground.
Test connection
1 = Sensor voltage
2, 3 = Sensor heating
Start the engine and warm it up so that the oxygen sensor can reach
its regular operating temperature. When the mixture is richened (for
example when the accelerator pedal is pressed down), the voltage
signal displayed must go up.
Display on voltmeter: 0.1 - 1 V
b) Checking the control unit
Raise engine to operating~temperature. Connect the exhaust tester to
the exhaust test tube. Disconnect the oxygen sensor and connect
the plug sleeve to ground on the control-unit side. Watch the exhaust
tester:
D24-18 LH-Diagnosis/Troubleshooting
Printed in Germany - XXV, 1990