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O2 Sensor Output - Good or Bad? (archive)

[ Follow Ups ] [ 7-series (E32) Message Board ] [ Msg. Board FAQ ]

Posted by Wayne McKay on April 03, 2001 at 13:05:44:

Thanks Rick Stillwell for your timely March 28 post on getting inside the DME connector to check O2 sensor output. I was just at that juncture in my diagnostics and was thinking there must be a way to do it rather than dropping the exhaust. Just saying it was possible gave me the incentive to rip at it.

Bentley suggests the output should cycle between 0.8V and 0.2V. Mine started properly at 0.45V until they reached operating temperature but cycled between 0.88V and 0.08V! The top end isn't too bad but way low on the bottom end. The engine is currently running rich and therefore rough at idle.
1) Could these readings be the cause (i.e. tricking the DME to richen the mixture),
2) the effect (i.e. leaking injector(?), etc., causing mixture to affect the sensors),
3) or neither?
4) Are the sensors still OK?
5) Does a rich mixture produce a higher or lower output?
Can someone please enlighten me...I am assuming ideal sensor output would have equal duration at 0.8V and at 0.2V giving an "RMS" output (feedback signal) of ~0.5V. Then as the O2 content changes, the relative duration changes producing a higher or lower RMS voltage to the DME which adjusts outputs (injectors, etc.) to bring the system back to the 0.5V setpoint.

'88 750iL 192k kms (119k mi)
P.S. Good to have you back Max!!

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