[torsen] Normal range of duty cycles on OXS Freq Valve?

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Mon Jan 15 19:29:02 EST 2001

Hopefully someone else has gotten back to you on this by now ... but since I
saw no reply posted ...

The OXS Frequency Valve is the feedback mechanism that Bosch added to the
CIS system to create the CIS-Lambda system (i.e. to incorporate the mixture
feedback from the OXgen Sensor).  The ECU applies a switching signal with a
controlled duty cycle (i.e. percentage time the valve is open compared to
the total time) to adjust the mixture to be more rich or lean.  

On Audi I-5 turbos like the WX engine in my urquattro or the MC-I engine in
my 5kCSQA the OXS Frequency Valve is a device with two radially configured
braided fuel lines and a two-pin electrical connector fitted around the
periphery, and which sits behind the fuel distributor and airbox near the
right inner fender.  IME the buzzing noise that the valve makes can usually
be heard over the normal running sound of the engine at idle.  On some
engines the ECU incorporates diagnostics which make use of the fact that the
ECU determines the duty cycle (like on the WX if you close both the idle and
WOT switches the ECU sets the duty cycle to 50%).  While it is possible to
measure the duty cycle with a standard dwell meter, there are handheld
meters you can buy which will read out duty cycle directly.  

Steve Buchholz
San Jose, CA (USA)
> ok, what's an OXS frequency valve?

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