Question for those in the know....

I removed the factory dump valve to clean it and check if it's working.



I decided to try and test it to see if it's the source of a whistle i'm getting under boost (and i'm now sure i'm not getting full boost). I connected up a small pump and tried pressurising the port marked 'A' on the pic. About 3 or 4 psi the air started to pass through and out port 'B'. Correct me if i'm wrong but this shouldn't happed at all unless port 'C' has been pressurised (as it would be from the pipe coming from the inlet).

I've tried pressurising port 'C' to between 15 and 20 psi (where i believe it should open the valve) but it make no difference to the airflow through from port 'A' to 'B'.

I reckon i've got a gubbed dump valve. Can anyone confirm or tell me otherwise or have i just wasted my time?

cheers,

Marty.

 

When its back on the car do you get a noise like blowing across the top of a bottle?
This happens about 3000 -3500 rpm with a good load on the engine (try going up hill with the throttle wide open). It will never be apparent standing still.
If so then yes, its sh4gged.
Well known fault on the MY97 engines.
Replacement from Subaru looks the same but seems to be lasting OK - or you could get a fancy pants stainless one suchas a Baileys BOV.

Nick

 

Butty,

The noise is more of a whistle. Sounds like an ambulance siren if you tap the accelerator then back off and repeat (much to my dispair and my nephews amusement). It comes in at about 2000rpm and goes up in pitch to about 3500 at which point you can't hear it anymore. The car is a 94 WRX.

cheers.

 

Port 'c' should be vacuum as far as I know.

Air should not pass through, a - b, as you say, until the vacuum opens the valve.

 

Cheers,

Looks like i'm off to find a new dump valve. Maybe then i'll see how quick a scoob really should be (it's been like this since i bought it).

Anyone in the West Yorkshire area got an old factory dump valve they wanna sell? Posted in 'wanted' section with details.

 

If this is the same as some other DV's I have looked at then pressure in C opposes pressure in A to stop flow from A to B. So with atmospheric on C (open) then it is quite easy to get flow.

When you let off the throttle then there will be a vent from A to B because the pressure at C has dropped (after the throttle) but the pressure a A remains high because of boost pressure between the compressor wheel and the throttle body.

Just my understanding from looking at the MY99/00 DV. Please correct me if I'm wrong.

So yours is probably leaking from your test by pressurising port C and you still get easy flow A-B.

At C, I believe it is vacuum that OPENS the valve and pressure keeps it shut.

[Edited by john banks - 10/12/2002 1:49:52 PM]