The correct way to do a Boost leak test ...

[BIGGSIE]

I have read almost all of the posts pertaining to boost leak testing and some DIY instuctions. Why is it that no one seems to tell us that you can pump air in the intake all you want but if the valves are not closed you will not be able to build pressure. My main question is can the camshafts be set (without removing the timing belt) so that all valves are closed?? I know the gears are marked for timing but when you set them some of the valves are still open. I am sure many of us have ran out to Home Depot and bought the supplies to build a tester, then hooked it up, put pressure to the intake and thought they had a huge leak. (I know I did. Also I know you can plug the UICP before the TB and test that way but then you can't test TB gaskets, inj. o-rings and etc.. Sorry for the long post but I had a heck of a time this weekend trying to chase a leak that did not even exsist. Thanks in advance for any help.

 

[Lordpaxin]

well,
I use a shop air compressor and a regulator

i insert the air through the turbo, leave the throttle body closed.
check for leaks in intercooler and pipe.

then i open the tb, and listen there.
so im getting a constand 20 psi with the regulator.

 

[Leitnin]

aren't there only 4 points where there will be both sets of valves open? If you are super unlucky, you will leave the engine right where one cylinder is overlaping intake and exhaust. if thats the case....turn it a little. It not likely to end up in one of these 4 positions...and if you turn it some, it should be in another one.....

 

[Ryan95tsiAWD]

heh...i got frustrated by that my first time too...but being a smoker and an engineer from the old school...

I tapped a "clean" vac line on my little home depot device right before the turbo, lit up a cigarette, and blew the smoke into the vac line(closed it off with my finger afterwards). I found several small leaks that i would have never found trying to listen or feel for them. my TB was the worst leak of all...

 

[Enigma_Man]

I've never had a problem with doing an intake leak test quickly and easily, without having to set up my valves any certain way.

Like the other guy said, you might get unlucky, and just happen to hit the spot where both the intake/exhaust valves are open and just lose all the pressure out the exhaust.

But if that's the case, just crank it over for a sec to move everything around.

It should work then.

I've done an ILT 10+ times now, and never encountered that. Keeping the TB closed doesn't keep pressure out of the manifold, it just goes around it through the ISC.

-Jesse

 

[steve]

Originally posted by Leitnin
aren't there only 4 points where there will be both sets of valves open?

It's a little more than 4 points but your generally correct. There is a range of about 30 degrees for each cyl when valve overlap happens and both sets of valves are open. On a 1G turbo it starts about 21* BTC exhaust stroke and ends 9* ATC. It's longer on NA 4G63's cause the intake opens at 26* BTC. So if you turn your crank to 15* ATDC before testing at most only one set of valves per cyl will be open, if I've done my math right

In practice I don't think I've ever had the engine stop in a position with a cyl in overlap when I went to test.

Steve