frequency valve operation?

Jukka Majanen jiipm at
Sun Jun 3 23:52:34 EDT 2001

Hi, maybe this is an old thread, but I saw no responses

Nick wrote:
> Can someone explain the operation of the frequency valve, not so much as
> what the ECU does with it but specifically what the three vac lines do,  and
> why on a 10V motor both wastegate ports are plumbed and only one on the 20V.

The hose under the bottom of the FV connects to the intake manifold.
Driver side line to the upper side of the WG and the third one connects
back to turbo intake. Some differences between auto and man tranny cars.

Lower WG line comes straight from the intake to open the WG at certain base 
pressure, which is some +0.2-0.3 bar. To raise the pressure, the WG spring 
needs some help ( pressure above the diapgram ) to keep close. This is made
by leading there part of the boost pressure. That is the reason 10vt has those 3
connections. FV oscillates between WG and intake to control the boost by ECU.

Newer cars have only one side to be controlled, more new have a stepper motor
instead of FV and most new have no WG, by pass controls boost ( VAG 1.8T )

My two pennies


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