740 Upped the boost. Now have boost leak...

745volver · 08-22-2012, 02:30 PM

The other night I adjusted the overboost switch which allowed me to crank up the boost some. Went from about 10 psi to 13 and now at WOT, at around 11-12 psi, there is a consistent whistling sound which I am assuming is a boost leak. I have had the mbc for about a year and it did not make this noise until I started running 13 psi.

Could the extra 3psi have caused a leak or have I always had a leak and this higher pressure is now making it audible?

All intercooler pipes and fittings are tight....

Are there any common leaks besides the obvious stuff?

I love the extra power but hate the noise!!

Car is no longer running BOV.

Lando · 08-22-2012, 02:36 PM

Check PVC box they like to split at the seam under increased boost.

745volver · 08-22-2012, 02:41 PM

What is the PVC box?

It only whistles above 11-12 psi.... If I split said box wouldnt it do it at any boost pressure?

Fitzy · 08-22-2012, 02:49 PM

http://forums.turbobricks.com/showthread.php?t=158981

Lando · 08-22-2012, 02:49 PM

No. Just because you can't hear the whistle all the time doesn't mean it isn't leaking all the time. Just check it. It's a little black plastic box below the intake. The large hose that crosses the valve cover leads right to it. Pry on the seam gently with a pocket screw driver and look for movement.

745volver · 08-22-2012, 02:55 PM

Ohh yes I know what your talking about..... Okay thanks guys I'll take a look

doucheNozzle · 08-22-2012, 04:34 PM

Quote:

Originally Posted by 745volver

Car is no longer running BOV.

Ooops. Or are you running the integrated CBV?

745volver · 08-22-2012, 05:22 PM

Quote:

Ooops. Or are you running the integrated CBV?

Sorry forgot to mention. Yes I reinstalled the CBV. I originally had a block off plate that was made out of some pretty thin sheet metal and I suspected that boost was leaking between the compressor and the plate....sort of something to the extent of when you put two pieces of paper together and blow through them and it whistles.

But the leak is still there after I put the original CBV back on

Also the PCV is in good shape. I pulled the line that connects back to the air intake and blocked it off so the crank case would vent to the air and the noise is still there...

doucheNozzle · 08-22-2012, 05:35 PM

Sounds like it's time to do a smoke test
What's the known condition of the turbo itself?

745volver · 08-22-2012, 05:41 PM

Never heard of a smoke test....

The turbo has the usual shaft play and cracked hot side of a 15g..... small amount of oil in the charge pipes and intercooler.

Turbo has been on the car without problems for more than a year

745volver · 08-22-2012, 11:41 PM

Made a leak tester and put 15 psi on the system....There is a leak under the fourth intake runner

Hoping it's simply a gasket failure. Will be pulling the intake tonight to see

Lando · 08-22-2012, 11:44 PM

Quote:

Originally Posted by 745volver

Made a leak tester and put 15 psi on the system....There is a leak under the fourth intake runner

Hoping it's simply a gasket failure. Will be pulling the intake tonight to see

PCV box is right under there...

745volver · 08-24-2012, 12:46 PM

Well to my surprise I found two leaks..... one was the intake manifold gasket had cracked and I had a bad vacuum line

After fixing these, the entire system from the compressor pipe forward held pressure.

As I was poking around the engine bay I noticed two exhaust nuts missing....replaced the nuts and the leak went away.

I assume that when boost is increased the exhaust gas pressure increases proportionally?

So to close this case all in all it was just a loose exhaust mani

08-22-2012, 02:30 PM	#1
745volver Board Member Join Date: Oct 2010 Location: Sacramento	Upped the boost. Now have boost leak... The other night I adjusted the overboost switch which allowed me to crank up the boost some. Went from about 10 psi to 13 and now at WOT, at around 11-12 psi, there is a consistent whistling sound which I am assuming is a boost leak. I have had the mbc for about a year and it did not make this noise until I started running 13 psi. Could the extra 3psi have caused a leak or have I always had a leak and this higher pressure is now making it audible? All intercooler pipes and fittings are tight.... Are there any common leaks besides the obvious stuff? I love the extra power but hate the noise!! Car is no longer running BOV. __________________ 1987 745T 207k. 15g at 14psi. M46 with homemade short shifter.

08-22-2012, 02:49 PM	#4
Fitzy Board Member Join Date: Dec 2005 Location: Belmont, MA	http://forums.turbobricks.com/showthread.php?t=158981 __________________ 06 s60R MT 84 242 Ti 4spd - A work in progress...

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08-22-2012, 02:41 PM	#3
745volver Board Member Join Date: Oct 2010 Location: Sacramento	What is the PVC box? It only whistles above 11-12 psi.... If I split said box wouldnt it do it at any boost pressure?

08-22-2012, 02:49 PM	#5
Lando Hunting with Ray Charles Join Date: Mar 2011 Location: SL UT	No. Just because you can't hear the whistle all the time doesn't mean it isn't leaking all the time. Just check it. It's a little black plastic box below the intake. The large hose that crosses the valve cover leads right to it. Pry on the seam gently with a pocket screw driver and look for movement.

08-22-2012, 02:55 PM	#6
745volver Board Member Join Date: Oct 2010 Location: Sacramento	Ohh yes I know what your talking about..... Okay thanks guys I'll take a look

08-22-2012, 05:35 PM	#9
doucheNozzle Emerged as Ugly Butterfly Join Date: Feb 2009 Location: Cub Scout Camp, CA 93405	Sounds like it's time to do a smoke test What's the known condition of the turbo itself?

08-22-2012, 05:41 PM	#10
745volver Board Member Join Date: Oct 2010 Location: Sacramento	Never heard of a smoke test.... The turbo has the usual shaft play and cracked hot side of a 15g..... small amount of oil in the charge pipes and intercooler. Turbo has been on the car without problems for more than a year

08-22-2012, 11:41 PM	#11
745volver Board Member Join Date: Oct 2010 Location: Sacramento	Made a leak tester and put 15 psi on the system....There is a leak under the fourth intake runner Hoping it's simply a gasket failure. Will be pulling the intake tonight to see

08-24-2012, 12:46 PM	#13
745volver Board Member Join Date: Oct 2010 Location: Sacramento	Well to my surprise I found two leaks..... one was the intake manifold gasket had cracked and I had a bad vacuum line After fixing these, the entire system from the compressor pipe forward held pressure. As I was poking around the engine bay I noticed two exhaust nuts missing....replaced the nuts and the leak went away. I assume that when boost is increased the exhaust gas pressure increases proportionally? So to close this case all in all it was just a loose exhaust mani