Unusual, rather loud, POP noise during boost leak test?

[IwantMKIII]

SO i did a boost leak test today set for about 15PSI. I found numerous as expected since my recent hard pipe install, my biggest one being a torn vacum line. I tightened the last clamp and finally everything sounded right. Then i put my ear up to the PCV hose from the TB to the intake. It was letting out a bit of air so i plugged it with my thumb. Once pressure equalled i heard a tiny hiss from the turbo outlet when suddenly POP! and what seemed like an internal (?) leak started. It came from the intake side of the engine? I tried to pick where it was coming from and found the loudest noise came from the vacinity of the intake side, lower, front near all the pulleys/gears for the timing belt? My other friend and i were stumped. It wasn't really a hiss noise like a real leak but it still sounded like something was leaking inside :1zhelp: . He recently did a HG on his '90 and cant remember anythign down towards that area that could essently POP like it did.


Any ideas? :1zhelp:

PS i drove it home today over 300miles and it seemed to hold boost fine, no out of the ordanary symptoms except higher then normal knock sensor readings probably from the gas i got.

 

[cuel]

Valve seal maybe? Knocked some loose carbon off of a valve seat? Pushed a valve open?

 

[SevenMKIII]

Sounds like you blew out the little plunger behind the ISCV in the intake manifold. Don't ask me how I know but it's a thought and only two bolts.

 

[GrimJack]

Sounds like you blew out the little plunger behind the ISCV in the intake manifold. Don't ask me how I know but it's a thought and only two bolts.

x2.

 

[IwantMKIII]

Valve seal maybe? Knocked some loose carbon off of a valve seat? Pushed a valve open?

that came to mind, but the heads were rebuilt with 3angle valve job less than 6K miles ago.

 

[IwantMKIII]

Sounds like you blew out the little plunger behind the ISCV in the intake manifold. Don't ask me how I know but it's a thought and only two bolts.

side effects of this? symptoms rather? Doesnt the ISC connect to a hose on the intake? or is that my imagination....if it does, wouldnt that hose then leak?

 

[jdub]

There's a check valve under the ISCV on a turbo motor. If you popped it, you could have a boost leak...the severity will depend on the how much it leaks. The hose attached will not leak (unless it's bad too) and the boost that does get past the check valve is metered air flowing right back to the accordian hose. You probably won't notice a thing...the ISCV will still control air flow for idle control. You'll just lose some power under boost. You'll have to pull the ISCV to check it.

Check all your vac lines in the intake manifold area too...especially the ones to the VSV's on the bottom of the upper intake.

 

[IwantMKIII]

^will do after this weather in the northeast calms down

 

[IwantMKIII]

There's a check valve under the ISCV on a turbo motor. If you popped it, you could have a boost leak...the severity will depend on the how much it leaks. The hose attached will not leak (unless it's bad too) and the boost that does get past the check valve is metered air flowing right back to the accordian hose. You probably won't notice a thing...the ISCV will still control air flow for idle control. You'll just lose some power under boost. You'll have to pull the ISCV to check it.

Check all your vac lines in the intake manifold area too...especially the ones to the VSV's on the bottom of the upper intake.

question....is it obvious to tell if i popped it? i've looked at it once but only breifly in the past and can't really remember what it looks like.