Legacy b4 Boost shudder .......help

legacy b4 rsk 2003, problem: first turbo boosting fine, when both turbos boost together after 4,500 rpm the boost raises to 1.1bar it then slowly fluxuates between 0.9 and 1.1 about 3 times and then the boost cuts and the whole car shudders.

sounds like the wastegate is letting off the boost asa it overboosts each time

originally had this problem with the stock blow off valve, took it apart and the gasket between blowoff valve and intercooler was in poor condition, used some gasket sealant and the problem went away, was boosting perfect again, so my diagnosis was that the small pin hole leak through the shoddy gasket was causing the car to overboost and the wastegate to go haywire.

installed a fully adjustable turbosmart blow off valve today, with a new rubbery cork gasket, and the problem is back, below is a picture of the set up, the turbosmart blow off valve is set to 100% recirculate back to turbo

and the problem is back, any ideas? would it be the new blow off valve? or should it be venting a certain amount to atmosphere?

sorry meant to post it here in the first place , not general chat.

The wastegate would be closed if over boost occurred.

Put the standard valve back on and see if it solves the problem , they run better with a closed / recirculating system

the problem does go away with the standard blow off, if i put it back on with the rubbish gasket and sealant, however the sealant eventually deteriorates and the problem occurs again, i can only assume its due to the leaky gasket that the problem reoccurs, having trouble getting a gasket made up for it, as its an awkward shape, that's why im hoping to get the new one working with it.

you can adjust the spring preload on it to fully recirculate back to the turbo, which is what I have done, so don't understand why the boost problem is happening

Would you not just buy one new off Subaru , about 15-20 quid ?

tried looking for one, couldnt find one for the b4 online, local dealer couldnt source one, if some one has a link or knows where to get one id appriciate the info

Ring Carroll and Roche Subaru, they'll sort you out

Gasket is same as v5/6 impreza.

So find hard believe main dealer cannot source

I don't think he's tried main dealer

Mechanic told me he had tried, looks like he either forgot or couldn't be arsed :banghead, out of curiosity does any one know why the car is behaving like this under acceleration, its a recyrculating valve (you cant see it in the picture but the recurculating valve is just behind it) and wouldn't the blow off valve be redundant during acceleration anyway?

Re: Re: Legacy b4 Boost shudder .......help

[quote author=garethmac600 link=topic=40419.msg1#msg1 date=1390054880]
Mechanic told me he had tried, looks like he either forgot or couldn't be arsed :banghead, out of curiosity does any one know why the car is behaving like this under acceleration, its a recyrculating valve (you cant see it in the picture but the recurculating valve is just behind it) and wouldn't the blow off valve be redundant during acceleration anyway?
[/quote]

No one can tell you issue on a forum as it could be anything. :-(

Ring c&r, get a new gasket and put the standard bov back on seeing as you say the car runs perfectly like that. Is the old recirc pipe blocked up properly? Looks like the way you have fitted the new one will catch the bonnet and maybe kink the pipe.

Yes the bov is redundant during acceleration unless it's leaking which is common on a lot of aftermarket bov's. Have seen loads of them give problems over the years.

ok so heres the update, buddy of mine managed to make me up a gasket for the standard one, so its all set back to standard now, havnt tested it yet, but will do 2night, :clocks:

the recurculating pipe, is not blocked off, as it is plugged into the side of the new aftermarket blow off valve,

the hose going into the top of the blow off valve is not kinking, as i have tried it when this hose has been tie wrapped down, and the same problem occurs.

did a bit of testing this morning, and adjusted the preload of the spring in the aftermarket blow off valve
results: when adjusted to fully recurculate (high tension preload) the problem occurs where it fluxuates and then shudders
when adjusted to vent to atmosphere and recurculate ( approx 50/50 at soft preload) when the boost kicks in the b.o.v just starts leaking and the boost just pours out ( similar feeling to having a huge boost leak)

so i'm thinking that the preload of the blow off valve has something to do with it, as the aftermarket one takes twice the force to push the valve in, and has twice as much travel.

and i am well aware that this has now got to the point where its just me being stubborn but god dammit i want to figure it out

and i appriciate all the help lads, this is my first turbo, and first subaru all in one, so youll have to excuse my ignorance

Took her for a long spin there, opened her up and shes driving like shes just out of the factory, still want to know what's causing the other blow off valve to not work

It just doesn't suit the setup simple as that