Car won't boost above 0.5, loud whoosh noise...please help
 

Just had Alpha 28's, headers, injectors, rear intake piping, y-pipe, TB, and plenum on my 2001 996TT that already had 16G, exhaust, I/C and softronic tune.

Everything was initially pressure tested to 20 PSI.

When the EBC is turned off, the car will not boost above 0.6 and when it gets to 0.6 there is a loud whooooosh sound as you continue to accelerate. When the EBC is on, the car will boost up to 0.9 bar and then immediately drop to 0.6 and hold flat at 0.6 with the same whoooosh sound. The sound does not get louder the faster you go, its just a constant whooosh.

We thought the intake piping was collapsing in one area, so we had a custom hard piece made to go in that spot...nothing changes.

My mechanic that did all the install is unfortantely out of town for 2 weeks (:eek:), so the other guy is going to re-pressure test everything and check the diverter valves.

I really hope its not the intake piping in a different area that is not accessible without dropping the engine!

Anything else he can test?

Thanks in advance for any help/comments!

Plan is to put the car on the dyno and try to figure out where the leak is...any comments on things to look out for etc... are greatly appreciated!

you have a boost leak, that happens at .6 bar be it either your diverter valves giving up or hoses not sealing.

how do I know if the DV is bad? I was told that running pressure through it won't work since the spring is set to 0.2 bar. I was told the way to test it is to put my finger in the bottom of it to open the valve and then put my thumb to cover the top manifold, move my finger andthe valve should stay open until i move my thumb...sound right?

(I have Agency DVs)

If the DV is bad, would it cause that whoosh?

i dont know about that test method,

they generally dont go bad as aftermarket units, does this whoosh sound, sound jsut like when you chop the throttle under power as normal?

without being there its hard to know if the whoosh your talking about is the DV's openign and doing their job(maybe prematurely) or if you have a boost leak which is generally more of a hiss but if its big enough it could be a whoosh?

I would not waste time with a dyno. I would run a boost leak test. Its not the intake piping so dont worry about dropping the engine.

the whoosh sound is a very loud sound that happens as soon as the car hits 0.5 bar (and won't go any higher). It literally sounds like a heap of air is escaping out of the back.

I think the DVs are opening too early....how is this fixed?

pressurize from the turbo inlets (cap one & pressurize through a cap on the other), that will test the DVs

I was told by Matt @ Vivid that running a boost test on the DVs doesn't work since the spring is set at just 0.2 bar....which is why I should use my finger to test them (does this sound right??)

My mechanic thinks the DVs are opening to early

there should be pressurized air in the lines going to the top of the DVs, That+spring pressure, should keep them closed. DVs open upon reaching proper pressure differential (vacuum in the top lines when you close the throttle and positive pressure in your y-pipe trying to go somewhere), so "opening early" is a misnomer. If you're WOT, they shouldn't be open at all, regardless of time.

Couldn't I just take off the diverter valves and cap the f-hose? If it still has the problem i can take the DVs off the list?

yep, that's one way, though there's a small chance the DVs could still be contributing to the issue (if there's more than 1 leak). But since your hearing a whoosh, I would expect it to be a fairly large leak.

so if my DVs are opening while I am accelerating, there is a problem with the DVs?

What about if the hoses were not connected right to the DVs...could that cause a whoosh?

I would guess a hose has come loose and is dumping all the boost once the system gets to 0.5 bar. Simply pressure up the system at the turbo inlet and listen for leaks.