Boost Leak Test - Question??

[Peepers]

So I did a boost leak test this weekend and I was able to address three leaks. The first was pretty loud. The vacuum line running of the Defi sender was torn. The second was the upper IC hose at the BOV – needed some tightening. The third was the infamous AFPR screw. I added tons of teflon tape and that solved that one. FYI: I think the teflon tape disinagrates by gasoline cause there really wasn’t too much on the threads from the last time I fixed that leak. Should I even be using Teflon tape ??

Once I corrected all those I could load in 22-25 PSI and all I can hear / notice was sounds coming/leaking from inside the head / valve cover. I also thought I heard the oil bubbling (like blowing bubbles) in the pan. I have a new PCV valve so I know that’s not letting air into the valve cover. Where else would it come from – valves? When you do a boost test, it builds up pressure thru the IC pipes and past the TB, correct? How much air can get past the TB considering it’s in the closed position? I know it’s not 100% air tight but how much air can really get into the head / valve cover?? Any ideas?

So before the fixes the PSIs were dropping rapidly right to zero
Now after the fixes I’d load in 25 PSI and it would drop quickly to 20PSI then a little slower to 15PSI and then from 15-10PSI was a lot slower and it seamed to hold 10-5 PSI for a lot longer but over all in the end it would drop to zero

I have a Defi electric boost gauge so I need to keep the ignition in the on position in order to keep track of how much boost I’m loading into the system – anyone see an issue with this?

Peepers

 

[Mr Peepers]

There is plenty of air that can go past the TB plate, enough to support a 2L engine at 700 rpm

Also, depending on where the engine was in its revolution, the intake valves on one cylinder may have been open(also closed ones without a good seal). Some air could leak past the piston rings to the crankcase and to the valve cover.

If the intake valve stems are leaking, air could also make its way to the valve cover and crankcase.

The turbo seals could allow air to leak into the oil return line into the crankcase.

Just possibilities.

-Peepers

 

[92DSMErdrick]

haha thats kinda funny. "Peepers" opens the thread and "Mr. Peepers" responds to the post.

When doing a boost leak test you should align your car to TDC, then count 6 teeth up on the exhaust CAM, and 6 teeth down on the intake CAM. Turn the motor over by hand until those new marks line up and then do your boost leak test. This way you have intake valves closed on 3 cylinders and you'll have the exhaust valves closed on the 4th cylinder. You'll get some air going past the rings on the pistons in 4th cylinder.

 

[yokotabrat]

Is the new PCV valve OEM? If not, I wouldn't trust that it's not leaking. Just unhook it from the valve cover really quick to check while you're doing your pressure test. The new one I bought from Autozone leaked worse than my many year old OEM valve. I ended up solving that problem by using the USPlastic check valve that's in another thread.

 

[Peepers]

I thought that was quite ironic too - Peepers and Mr Peepers ... ... I guess I beat Mr Peepers to the name ....

I'm going to try the TDC + 30* boost leak test tonight and see what happens? The PVC is new OEM so I don't think that's the issue. I was going to also try the boost test off the lower IC pipe and not the compressor housing and see what happens??

Should our cars hold say 20 PSI and not drop at all or am I expected to see the PSIs eventually drop to zero? If so, how long sound this take??

 

[Street_Killer]

wtf does peepers mean? It should drop, if I remeber right. 10 psi every 30 seconds, if everything is sealed really good.

 

[Mr Peepers]

I was about to say something until I saw 2002

 

[Peepers]

Yesterday I did the boost leak test again with TDC + 30* and here are my results.
I loaded the system with 22PSI. It took approx 70secs for the boost gauge needle to drop from 22PSI to 10 PSI. Then from 10PSI to zero was about another 130-150 secs. When the gauge hit 12 PSI is seemed to hold more steady and the dropping of PSIs slow right down.

I couldn't find any external boost leaks but I could still hear the bubbling / hissing sounds coming from the head / valve cover (with the oil cap removed)

Do I need to worry? How do my numbers look?
Peepers

 

[romeen]

Yesterday I did the boost leak test again with TDC + 30* and here are my results.
I loaded the system with 22PSI. It took approx 70secs for the boost gauge needle to drop from 22PSI to 10 PSI. Then from 10PSI to zero was about another 130-150 secs. When the gauge hit 12 PSI is seemed to hold more steady and the dropping of PSIs slow right down.

I couldn't find any external boost leaks but I could still hear the bubbling / hissing sounds coming from the head / valve cover (with the oil cap removed)

Do I need to worry? How do my numbers look?
Peepers

The rate of pressure loss is not bad at all. As long as your PCV valve isn't leaking and the car is running well I wouldn't necessarily be concerned. There are 3 main locations that can leak air into the crankcase when doing the leak test, the first two are generally normal.

1) If you are doing the test from the compressor inlet then you will get some air getting past the turbo's oil seals, into the return line and thus into the crankcase. Since the motor is not running there is no oil pressure to seal it. This is not necessarily a problem as long as you have good oil pressure when car is running and you are not burning oil through the exhaust.

2) If you did the test on a cold engine then you will get air past the piston rings. You can try repeating the test on a warm engine to see if there is less leakage/slower rate of pressure drop.

3) As mentioned before, our PCV valve are notorious for leaking, even the new oem ones. If you haven't done it already, repeat the test with the PVC valve unscrewed from the VC but still attached to the vacuum line connecting it to the IM. Check for air leaking past valve. If it is leaking you can use the check valve that yokotabrat mentioned. I've had mine for about a year and it is still holding tight.

http://www.usplastic.com/catalog/va...oduct_id=15641&variant_id=64175&cookie_test=1