SimonH

I know this is old hat but my MY00 has recently started making the mooing noise on lift off that I believe signals a leaky dump valve.

Using my acute technical skills I've had a look and can't see any obvious leaks or pipe disconnections. Is this sort of thing usually the cause or is it more likely to be a fault within the actual unit itself?
Also is it actually causing any damage to the car running it like this or does it just mean I'm loosing out on performance (or not even that)? I assume that it's just similar to a vent-to-atmos dump valve only that the sound is more Fresian than Forge? Given that my car works on a recirc system, I guess a leak (or vent-to-atmos) is a bad thing?

I'm going to get my dealer to take a look but seeing as I'm hoping to up the boost in the future would I be better off getting a better quality aftermarket unit?

SimonH

Anybody?

Or perhaps I should start a thread about left handed, green Sport drivers or one about how my Impreza goes faster than your bicycle - those usually generate thousands of replies......

RichiW

hmmm,, i`ve recently fitted a Forge VTA and i now suffer from more of a "meeeeoow"(sounds like a cat o.k.!!) as i roll the throttle on.

Same thing??

Rich.

SimonH

Rich, not quite - the noise only occurs when I lift off the throttle...

Anybody else?

MattRus

Simon,

the valve is designed to open when you lift off, this helps prevent damage to the turbo. Basically, at lift off a partial vacuum is present in the manifold which in turn acts on the valve diaphram, opens the valve and vents any pressure present between throttle and turbo to atmosphere or back into the inlet ducting.
The 'moooing' I can't dircetly comment on but it could be a damaged valve (diaphram leaking, or piston sticking). Have you noticed a drop in achievable boost? If so the valve is not closing properly so could be sticking. Remove the valve and check that the piston moves freely by pushing it and letting it return to it's seat. While you have it out clean the valve seat and piston face with clean rag or tissue.

SimonH

Thanks for taking the time to reply Matt - perhaps "mooing" is a bit of a crap description; it's like a blowing-over-the-top-of-a-bottle sort of noise.
Achievable boost appears normal on the gauge so I assume it's not leaking when the system is under pressure; the noise occurs on accelerator lift-off when the dump valve is doing it's job and trying to dump the excess pressure. I guess it's not opening properly.
Thanks for the tips - I'll get it apart and take a look.

Neanderthal

iTrader: (6)

My standard re-circ dump valve broke (common fault on MY97's) and it made the "blowing over the top of a bottle noise" for some time. By the time I replaced it the noise had gone to a fog horn

Is your dv plastic?

Matt