Hi, Ive got a v4 sti and it seems down on power and is very jerky on overrun. Been driving with the window down and wot in fourth i can hear what seems like a fairly load air noise and when lifting off a slight hiss which i put down to the standard dumpvalve, just looking for some ideas, Oh the only mods are a decat and panel filter but no boost gauge. If it was a leak from the exhaust before the turbo that would just sound like an exhaust blow?
Cheers
James

 

Yes it would just sound like it was blowing.

I think you would hear the boost leak more with the window up, and sounds like its coming from the dashboard.

Its a possibility that you have an air leak due to the rough running your getting.
Check all the pipes on the inlet manifold and that the blanking plug is still on the spare nipple.
I would then check the dump valve is operating correctly.
Might as well check the boost pipes for cracks/splits and the intercooler hoses.

 

Cheers for the reply mate, How can i check the dumpvalve

 

Swap it for one that is in good working order.
If you can't do this remove it and see how difficult it is to open it (this might not be a great way to diagnose it as you don't know how difficult it should be)
The alternative it to block it off and run without a dumpvalve* just to see if it makes a difference. You have to make that decision though, as there is a possibility that it can cause damage to the turbo.

 

Thanks for the reply shmerman, I could run it without the valve just to see if theres any difference and then put it back on.

 

A boost gauge would be really valuable here as you are likely to perceive the car is much faster due to the extra noise it is going to make with the dumpvalve blocked off.

If you can get hold of one sooner rather than later, that would be better. You can then see what boost you are getting before/after.

 

Im going to look for one now