Just a quick question. Does the O2 simple verify things are working or does it have a function relative to duty cycle. I adjusted my lambda and get about 15mpg highway or city in my 560 SEL. I installed a new O2 sensor and using its voltage adjusted lambda and dropped to 13mpg. I adjusted back and all it okay again.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

The fuel computer (ECU) uses the O2 signal to change the lower chamber's fuel pressure.
That is done thru the EHA.

The principle of CIS is all about the pressure differential at both sections of the fuel distributor.

The signal from the O2 sensor allows the ECU to slightly change the lower chamber pressure

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Thanks. I also just read the Jetronic book. The system seems to be incredibly responsive to the O2 sensor output, much more than I am used to. In other words, using O2 voltage is pointless other than to verify the O2 sensor is working correctly.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Yeah, you're much better off measuring the duty cycle at the circular diagnostic port, and adjusting the lamda from that. There are several good write-ups herein.

DG

In case someone searches upon this thread, here is the write-up I used to adjust lambda.

http://www.landiss.com/mixture.htm

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car