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Old 09-01-2003, 08:50 PM
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zorin zorin is offline
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Join Date: Feb 2003
Location: Ottawa, Canada
Posts: 126
Exclamation Duty Cycle / Bad O2 Sensor ?

Hello group,

The '86 300E is having rought idle . I checked the Duty Cycle on diagnostic port while the Engine was running (operating temperature) , it is stuck at a very low number (7 percent). It used be hovering around 50 percent few months ago. I am not sure what would cause the wrong reading now.

I did the following tests:

- Disconnecting the O2 sensor corrected the duty cycle (showed 50 percent) .
- Disconnecting the temp sensor plug going to ECU made no difference in reading.
- Disconnecting the temp sensor plug going to ignition control unit increased the duty cycle.
- Checked the voltage at the output of O2 sensor , it is about 480 mV which I think is the correct one.

Does this mean I have a bad O2 sensor , a bad temp sensor plug or something else?

Any suggestion is appreciated.
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Zorin

'88 Benz 420 SEL
'79 Porsche 911SC ('87 Carrera Engine)
'00 BMW 540 Sports Package
'99 Land Rover Discovery

86 300E - Manual (sold)
88 260E (sold)
84 944 (sold)

Last edited by zorin; 09-03-2003 at 12:57 PM.
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