Mark knows this staff

 

I am not questioning Markski's recommendation and advice. I have read through enough posts to know, other than when he has Jet Lag, he is pretty accurate in his assessments of people's P-car issues.
I have made a few more pressure testers with the recommended tire stem. See attachment. (if I am going to make one, might as well make a couple)

I will run some pressure tests with the new set up as soon as I replace my Check Valve #16, Venturi Tube #9 (that have check valves built in), and my two Check Valve #21's.

I like to know how and why things work they way they do. I have tested the new #16 and #9 valve/tube to see how they work and map out the air flow. When I get the old ones out I will see if any are bad. I can understand why people say they won't hold much pressure. The diaphragm/valve in those things feels pretty weak.

So now on the topic of me doing the pressure test wrong by hooking up my air compressor to the drivers side turbo, setting the air compressor pressure regulator to 20 psi and confirming the 20 psi of pressure on the passenger side turbo. Verses using a Tire Valve Stem on the driver side and pressurizing the system to 20 PSI and locating the leaks.

From the 100+ posts I have read, the only reason I can come up with as to why the constant air compressor 20 psi pressure method is not good is because most check valves are rated for ~15psi and I could just be constantly overpowering them creating the perception of false leaks. If I were to run the tire valve stem method it would bleed down until the weakest check valve held.

My question regardless of the method, If I am planning to run 19+psi, then I will still be overpowering the check valves. I have inquired to see if anyone makes any stronger check valves, and only found one thread where someone said they found a similar Mits Evo check valve that was rated to 40psi. (But no part number)

One question I have regarding all the check valves... And I can't tell from the diagrams that don't tell me where some of the lines terminate at. Would any failed check valve cause metered air to bleed out of the "system" or into atmosphere? Because those would be the ones that would impact my performance greatly. The others, if they fail and bleed metered air back into the system just reduce efficiency.

 

your over thinking...
ziptie all vacuum lines... change any cracked ones... especially the ones at the N75 valve... and FPR...
we do run 28 psi on existing set ups and they hold if done right...
I will not get into a discussion why my method is better then yours... I am extending my time telling how to stop the drama and do it once right... what you do is up to you...

if you have the compressor running all the time and putting constant 20 psi you cannot find the leaks... thats what you you have to put air in.. close the system... make sure its quiet so you can hear the problems... start touching the lines on an on.. you will hear the difference in hissing sound.. spray some soap and water... and go from there... thats how you find em... one at a time...
Ive had a shop do what you did for 2 years and they never found anything.. no wonder why the cars ran like crap... it was until a client took a video of what the mechanic was doing that I caught on to what was happening... and they were doing same as you..
good luck.. Im done gotta go.
markski

 

Markski - I do appreciate the input and your experience - Thank You.

As an update:
#16 check valve was sticking open. Once it was pulled from the car, you could get it to work, but you could hear the diaphragm "popping".
#9 Venturi was also bad. It would not hold more than 5 psi on a hand pump.
The new valves hold 20 psi.

I also tested the Plenum check valve for the oil reservoir and it would hold 20 psi. I am hoping to also check the #21 check valves and replace them as well. I will then put everything back in and pressure test per Markski recommendations.
-Shawn

 

I'm cross-posting my own post from the other boost testing thread into this one since you just did this, and this thread is getting the replies as of now. I'd appreciate some insight on the work you just did. Thanks in advance.


Can someone help clarify the procedure of what needs to be blocked off if testing is done at the throttle body?

I did a pressure test when I first got the car, installed new DV's & boost hoses and things were going pretty well. I took care of a couple of leaks, but always had a slight hissing when above 15psi. At 5psi it would hold steady, but I don't want "good enough". Now that I've read more I want to give it another go and I'm thinking there's a decent chance the check valve going coming from behind the TB and going to the drivers turbo may be the culprit.

Part number 996-110-135-70 #16 on this diagram:


However, I'm guessing this needs to blocked to do the testing I'm suggesting?


When I go at it again, I'd like to test behind the throttle body.

So my assumptions are:
1)remove y-pipe & throttle body, make adapter plate to test pressure up to 20PSI

2)try to make a better seal on the oil filler cap with a rag or such


Questions:
Q 1) Does anything else need to be blocked off if doing it behind the throttle body plate? (assuming I try to tighten seal on Oil filler cap)

Q 2) What is the best way to jump the starter to turn the motor some if it's leaking through open valves, or is this even worth attempting?

Q 3a) If it is indeed the check valve mentioned, or one of the related check valves, whats the best way of testing / accessing to replace? I was planning on using the soapy water test to look for bubbles.

Q 3b) Do the DV need to be removed so you can even access view of it?

Q 3c) Does the motor mount bolts need to be lowered to access it?

 

I am becoming intimate with the vacuum/pressure lines on the 996 turbo. Here is what I know and hopefully it will help with your testing...

The boost/intake hoses are pretty self explanatory. Things get interesting at the Y-pipe, throttle body and the plenum behind the throttle body. These are the parts with the vacuum/pressure lines that go off to other areas.

I will also try to provide pictures and I will answer questions I had asked earlier as well.
- The Y-Pipe has a couple of nipples - one comes off the #9 venturi tube and the other goes to the N75 waste gate control switch.
- The TB has a couple of nipples. They have the #21 check valves connected and the best I can tell, they are designed to hold vacuum. (My #21 check valves were working and held 20 psi. I have new ones and will most likely replace them anyway) I need to better map out where those lines terminate. They are 1/2 white and 1/2 black. (#21 check valve - 964-110-950-01 ($13/ea))
- The plenum is where people seem to experience the most issues. I know I did. This is where the #9 venture tube also connects, as well as the #16 check valve and oil reservoir vacuum hose.
------- #9 Venturi Tube - routes into the Y-pipe with a check valve, and it looks like it also goes to the Brake Assist line. (With another check valve) The line going to the Brake Assist was broken for me. It would not hold more than 5 psi of pressure and was leaking around the outer edge to atmosphere. (Replaced - 996-110-652-70 ($50 local dealer with PCA discount)
-------- #16 Check Valve - goes into a T. One side of the T goes back into the intake before the drivers side turbo and is still in the metered system. The other side of the T goes off to what I believe is the Evap system/fuel tank. Mine was sticking and when I checked it in the car, it was stuck open. Once it was removed, I was able to free it, but you could hear it sticking and making a "popping" noise under vacuum and boost. (Replaced - 996-110-135-70 ($27))
--------- Plenum Check Valve - The plenum itself has a check valve built into it. It is the large hose on the passenger side that goes Oil Reservoir. It is designed to prevent boost pressure from going into the oil system. I tested mine to 20 psi and it held. The other two ports are wide open and go to #16 and #9.

I am putting things back in, and will pressurize the system to verify that none of the hoses, or clamps are leaking.
-Shawn

 

mbgt72,
Disclaimer - this is coming from someone who has yet to perform a successful pressure test. (But I have found issues with DV's, #9 and #16 so far.)

Questions:
Q 1) Does anything else need to be blocked off if doing it behind the throttle body plate? (assuming I try to tighten seal on Oil filler cap)
I think this test would help localize issues, but I would start at the turbo's

Q 2) What is the best way to jump the starter to turn the motor some if it's leaking through open valves, or is this even worth attempting?
I am going to see how lucky I get without rotating the motor. I did test the check valve in the plenum which goes into the oil system and it checked ok for me. If I need to rotate it, I will just turn it over with a quick blip.

Q 3a) If it is indeed the check valve mentioned, or one of the related check valves, whats the best way of testing / accessing to replace? I was planning on using the soapy water test to look for bubbles.
Soapy water showed my #9 leaking, but it did not show any issues with #16. It wasn't until I pulled the hose from the plenum to the Check Valve and put a pressure tested on it that I noticed it was stuck open. What was odd, was I was not leaking air down the #14 line.

Q 3b) Do the DV need to be removed so you can even access view of it?
I did not remove the DV's. See picture above.

Q 3c) Does the motor mount bolts need to be lowered to access it?
The motor was lowered to gain access. Otherwise it was just way too tight for my hands.

 

My boost comes on pretty lazy at times and I'm suspecting it's my #16 valve acting up. I've ordered an OEM replacement so I have it ready when I pressure test.

Though part of me can't help but think there's a more durable substitute out there for this common problem. The #16 valve does get whacked around as it's seeing full boost on one side and active vacuum on the other so the differential it's checking is pretty large.

Back when I turbo'd my Lexus, I used a toyota check valve and those were beefy metal parts compared to this plastic job. I didn't do it this time but if I have to replace this again, I'm going to try this substitute:

part# 4473024020

 

what psi is it good for?

 

That's definitely a good question. Though I don't have any hard facts other than anecdotal evidence that check valves never seem to be an issue with Toyota's. This same check valve is used on the supra turbo's for the brake booster and people regularly run them well into 1.5 and 2+ bars.

I can't vouch for them in this application, but wanted to throw the idea out there.

 

Hi like to acknowledge this thread as a great source of learning, have followed the testing and found a number of leaks in my car and have replaced many hoses and valves as a consequence, so making progress for sure.

Problem I am struggling with is I can't do the test as per markski directions and hold pressure for more than 3 or 4 seconds, I know where the air is going but can't do anything about it!!

It's going from the turbo cold sides and into the CHRA and then to the crankcase, I can clearly hear this by removing the turbo sump plus and it's loudly escaping.

I then took the new A28s turbos off the car and bench tested the cold side, same result, pressurise up and 3 seconds later it's all gone out through the CHRA.
I as a reference checked my old K16 turbos they held pressure for about 20 seconds and only lost about 1psi second out thru the CHRA.

Any suggestions please, am I doing this wrong or have wrong expectations?

Thanks
Mike

 

Just stop,
pressure test at the lower boost hoses after the turbos... simple... needs to hold 20 psi for 30 seconds... bypass the turbos...

 

Thanks markski, I have done that and all is leak free, was only concerned about the leak via CHRA and maybe pressurising the crankcase
Thanks
Mike