[W126 Coupe] O2 sensor absent 1992 W126 560SEC - CIS-E guru needed

[Paul Miller]

Hi all

I have been reading the lists about O2 sensors and in particular the
articles on adjusting idle mixture using voltage from the X13 sockets pins 2
and 3.   My voltage here is 6.7 volts FIXED no matter what I do to the
mixture .    

I suspected a faulty lambda sensor, but when I went to look I discovered my
560SEC W126 1992 ( Euro spec ) does NOT have a lambda (O2) sensor.  It does
not have cat converters either. ( FROM FACTORY ) 

The wiring for the lambda sensor is PRESENT on the floor of the drivers side
(RHD) although the 2 pin plug ( to supply heating ) I think should have 12
volts but has no voltage at all with the ignition in the 2 position.    The
single plug has a factory looking bung in the end of it identical to the
plug on a lambda sensor wire.

I suspect this means my CIS-E unit is always in open loop and If I connect
up a lambda sensor ( get a hole put in exhaust ) I can improve my fuel
economy by changing to closed loop.  Is this possible ????.  I currently get
22 mpg ( 17.6 miles per US gallon ) at 75 - 80 mph steady on the motorway
a/c off. 

Will I need another control unit that knows about the lambda, all are they
all the same ? 

Where does the 2 pin plug with the 12 volts for the heater part actually get
its power from, does the ECU tell it supply power to once it detects a
lambda sensor present or will I need to add some other connections.

Regards

Paul 


1992 560SEC W126 ( H&R springs, AMG AERO 1, stainless dual pipe exhaust )
1994 E300D  W124 ( bog standard 35 mpg on veggie oil !! )