# frequency valve, what does it do?



## vdubsir (Dec 8, 2009)

83 GTI 8v 2L ABA/1.8 hybrid, 272 cam
Can anyone tell me exactly what the frequency valve does as it pertains to fuel flow or pressure? 
I know that it changes duty cycle dependent on the 02, WOT, etc. but is it just an emission thing? 
My freq valve is not making the common buzzing noise and I'm wondering if it's actually effecting my motor enuf to cause problems? 
Also looking at the wiring dia I have, it shows a Oxy sensor control unit, where the F is it located? I finally found my O2 relay and things seem like they're doing what they're supposed to. 
Any help would be awesome!


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## WaterWheels (Aug 14, 2005)

*Re: frequency valve, what does it do? (vdubsir)*


_Quote, originally posted by *vdubsir* »_ Can anyone tell me exactly what the frequency valve does as it pertains to fuel flow or pressure? . . . but is it just an emission thing? . . . it shows a Oxy sensor control unit, where the F is it located? 

I guess in a nutshell it controls diferential pressure to maintain the correct, or close to it, fuel mixture as sensed by the O2 sensor. No, it is not just an emissions thing, it is an early attempt to maintain a good air/fuel mixture under all conditions, or as many as possible using the technology of the day. Should be located in the cowl. I highly suggest the purchase of a good repair manual, or even a bad one, and maybe a book on CIS systems.


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