Boost Leak Testing

[DoubleD]

I have a 92 IROC R/T with a HE 341, last season I was having issues with the boost gauge fluttering while under boost, when the boost was above 15, min boost with this wastegate is 18, so there is a problem there. I took the opportunity this winter to replace most of the Intercooler piping, I had a cobbled mess of rubber, steel and aluminum. I replaced everything with 2.5" Aluminum tubing and silicone couplers with quality clamps. I built a slick little pressure tested and I was pressure testing the system last night.

First I tried pressure testing the entire system and put the tester right before the turbo inlet, would not hold any pressure, air leaks were large enough to not see much more than 5 psi on the gauge.

Secondly, I took and removed one of the cold pipes pre-intercooler and capped it. I isolated the turbo and it still didn't hold any pressure, Should the turbo hold pressure?

Lastly, I took and put the tested right after the turbo outlet, I re-connected the cold pipe I disconnected pre-turbo and tried again. This time it would sorta hold air, but you could hear it hissing out down by the throttle body.

I am not sure what to do next nothing holds pressure, should the Throttle body be sealed and hold pressure from entering the IM.. Looking for some direction here.
Thanks

[wallace]

I would disconnect at tbody and turbo outlet. Plug both ends and test the whole thing at once.

[DoubleD]

I did a bunch of trial and error last night, isolating parts of the system, I found all of my new tubing and couplers with clamps are good and solid, I found the leak was coming from the bottom of the throttle body, I believed it to be the IAC valve o-ring, but I have not figured that out yet. I have a spare throttle body and I slapped that on and it fixed that issue. Pressure tested the system up the the turbo outlet and everything sealed well. Next to isolate the turbo and test that.

Does anyone know if a Holset turbo should be able to hold pressure from inlet to outlet?

I may pull the turbo off the car and test it on the work bench.

[DoubleD]

I did another round of testing and removed the turbo from my boost leak testing, I put my tester post turbo on the upper inter-cooler pipe before the inter-cooler. I found two leaks, the Fuel Pressure Regulator fitting was leaking (I have an Foward Motion adjustable one) and the Idle Air Controller was leaking. Is it common for the IAC to leak and where can I find a new O-ring to replace that one? The leak is not large, I can pressurize the system to 25 psi and it will take over 2 minutes for it to bleed out. I just want it sealed up and pressure tested as best as I can. Also found out my blow off valve starts leaking above 25psi.

[guyd_15]

Any decent hydraulic shop should be able to match up your O-ring.

Guy

[DoubleD]

I had a spare one that I brought to work, just got back from maintenance and I matched it up with a replacement. The AIS motor O-ring can be replaced with an AS568A Standard Sized -018 O-ring. The one on my car is a brown color and really hard, but I am replacing it with either a Buna-N or a Viton one, I don't know which material I have, but both are fuel resistant.

[zin]

If it takes minutes to leak down, you don't have a problem, the turbo is constantly replenishing the air supply, so a leak that small won't amount to anything, significant leaks will overwork the turbo and kill power, but that's going to be an obvious leak.

Great that you tested at all, most don't and could have significant leaks, but never know it!

Mike

- - - Updated - - -

If it takes minutes to leak down, you don't have a problem, the turbo is constantly replenishing the air supply, so a leak that small won't amount to anything, significant leaks will overwork the turbo and kill power, but that's going to be an obvious leak.

Great that you tested at all, most don't and could have significant leaks, but never know it!

Mike

[DoubleD]

Replaced the o-ring on the AIS motor and that leak is now gone, safe to say any noticeable leak is sealed up now. Car takes a few minutes now to bleed off all the pressure, only noticeable leak now is the rings, not much I can do there. I am happy with the outcome now.