how do you test for boost leak? and what is the best way to do it? can you damage anything by doing it? i want to get my car in top running condition before i start modding too much and want to do every little thing i can to make sure it is in top running condition and i'd figure a boost leak test would be a good way to start and i just didn't know how to do it. i was reading somehting form club DSM about cutting a bicycle pump hose in half and doing something with it but i was wanting to know all my options on doing it.

you need a valve from an old rim or bicycle tire, (2) 2"pvc "caps", a length of 2" flexible tubing to be clamped over the caps and a reducer that will be clamped onto a cap and the turbo inlet. (I forget exactly how big the turbo inlet is, I think it's 3.5")
You need to drill a hole in the caps and use glue or epoxy to mount the air valve in one of them. Then you'll clamp the tubing tightly around the cap and the other end over the other cap, the reducer over the end cap and big side over the turbo inlet.
Make sure all the clamps are tight and then use a bicycle pump with pressure guage to pump like 15 psi in. Then just listen for leaks.

vfaq.com

Go there, they have this exact faq with pics.

Also, consult that site for every basic thing you need to get the car running. It has everything.

http://www.vfaq.com/mods/ICtester.html
thats the link.
The one I described is the same, except mine is longer to make it a little easier to get to.

I clamp a same-diameter copper pipe end in place of the intake, and connect my air compressor to the outlet nipple with a piece of vacuum line. Good for about 30psi if you have no leaks.

i'm actually about to do this tomorrow. I think its my LIC pipe, which blows because I don't wanna buy a new hard pipe just to replace the turbo in a few months, but i'm def. misfiring. Its good that you're checkign the boost leak, but I think symtoms are heavy misfire or heavy loss of power under boost, and if you don't have one, you don't have one.


One question I do have, though, is what do you do about the BOV? do you have to plug it in any place when doing this test if its aftermarket? (for example, the greddy type S?) Or in his case, do you have to plug the stocker?

vandy

Originally posted by Vandy420a
One question I do have, though, is what do you do about the BOV? do you have to plug it in any place when doing this test if its aftermarket? (for example, the greddy type S?) Or in his case, do you have to plug the stocker? vandy

What do you mean by plug? You mean physically cover/fill the outlet(where the air comes out) of the BOV? It wont/shouldnt leak under pressure. Otherwise, how could you build boost while driving it? Hope I answered the right question.

If it's leaking from the BOV, thats where you'll hear it. :P
BOV shouldn't open without vacuum from the pressure source anyway.

ok so you dont' have to plug the dump tube? I guess that makes sense, but the throttle plate is closed when doing the test, so wouldn't that make the BOV open? Isn't that how a BOV works, when there's built pressure but a closed throttle plate?

Vandy

or maybe i'm just confused...

:shrug

When the throttle plate closes, there's suddenly a bunch of air pressure "piling up" in front of it, and a "big vacuum" behind it. The BOV is opened when a "big vacuum" condition occurs, and eventually springs back shut when all the "piled up" air pressure is gone.

This is why most aftermarket BOVs have an adjustment screw, to control exactly when the BOV opens. Typically you adjust the BOV to just barely shut at idle -20inhg or so.

If the engine isn't running there is 0psi in the manifold, and the BOV will be VERY closed. You would have to use a vacuum pump to get it to open during a boost leak test.

Feel free to slam me if I'm wrong, that's how I understand it so far.

cool, thanks! :thumbsup

another thing I'll throw in is that even though the throttle plate is closed, there is still a passage that allows air in. That is how your car can idle when the throttle plate is closed. The BISS screw is what opens and closes this passage.

Actually its the IAC that contols idle, the BISS just allows the idle rpm to be adjusted.

Originally posted by SaberKhan
BISS just allows the idle rpm to be adjusted.

by allowing more or less air in, yes?

Originally posted by eclipzGST
there is still a passage that allows air in. That is how your car can idle when the throttle plate is closed. The BISS screw is what opens and closes this passage.

The BISS is not what opens and closes this passage, the IAC is. Think about it, how could a screw open and close itself? The IAC is a stepper motor that gives/takes signals to the PCM and constantly adjusts itself in %'s. The IAC has a pretty broad control, up to 27% throttle I believe.

Gotcha.
I just always assumed the the BISS had something to do with that passage. I knew it didn't "open or close" it but I figured that by screwing it in, you partially bloked it causing idle to lower and by unsrewing it, you opened it up causing it to rev higher.
I never got into in depth discussions about the throttle body before. Thanks for setting me straight. :cheers