I had a boost leak that we could not track down for a while. How I found it was pressurize the system like you normally do and then grab the pipping by the couplers and start moving it around and listen for leaks. Do this for each joint. I had a leak on the coupling right offf the turbo and it wouldnt leak until I moved the piping around. It was evident when going WOT though.

 

EvoTech, THAT is the kind of info I was looking for.
I'm off to re-re-test. Thanks.

 

I had a variable boost leak that bugged the crap out of me for about 2 months. Typically came on after some spirited driving and showed up as not boosting well at all ...max boost then was 20 psi but sometimes it would only hit 15 and leak down rapidly.

I too tried all the boost testing. I found one leak on the lower ic piping, fixed with tbolt clamps ( i did all of the clamps just in case ) But the following week after sitting over the weekend the leak was back.

I started looking at testing the TB seals but realized there was one other place a leak could happen AFTER the TB. That is the PCV valve running from the valve cover to the intake manifold on the passenger side. That valve has to be open at vacuum to draw in vapor from the valvetrain but must remain closed at any boost condition.

Problem is under vacuum, it draws vapor and oil vapor int through it. When it sticks open you cant boost well and the boost drops dramatically ( at least it did on my car ggrrr)

SO went to Advance and bought a replacement for $10. Popped it in and ...no boost whatsoever....WTF had Advance give me another...lasted five minutes and showed same problem as stocker. Ended up going to MItsu and getting a new stock one. Bingo.... worked like a champ full boost , normal taper. Problem fixed right ??? UH not quite....Problem re-surfaced after about one month. This time I cleaned the little rascal with TB cleaner. Fixed the problem again. However it was getting clear that the REAL issue was the oil getting into the valve and not allowing it to close properly under boost.

Here's how to test it....Remove the valve from the car by removing the clamp on the vacuum line and then unscrewing the valve from the fitting going to the valve cover.
Wipe the valve off then blow hard into the threaded end. It should pass air freely. Turn the valve around and blow hard into the hose fitting end. It should not pass any air at all. It should snap shut and not leak . If it does, then clean it with TB cleaner from the threaded end. Test it again. If it is better, then you found your problem . If it does not get better, replace it. Do what I did though and test it at the parts counter by blowing into it from each end. Mitsu isnt known for the best quality parts either

So I designed a dual catch can system, one can for the valve cover to pcv to intake manifold line ...and one can for the valve cover to turbo inlet. This has permanently fixed my problem, no issues for 9 months now, including track days.

You must have the stock pcv valve on the intake side of the catch can to avoid pressuizing the can, so plan accordingly. Also I clean them out about once a month. I was quite surprised to see water in the PCV line can last month..evidently the beastly cold weather causes some condensation to occur that is trapped too. If it froze the valve, that could cause additional problems.
Could be that Mitsu erred on the safer side, thinking that oil couldnt freeze and that it is a replacemnt part , and if it doesn hold boost fully at least it isnt going to blow the engine?

Let me know if this helps at all

Milburn

 

THANKS Milburn, that was also extremely helpful. I feel better now, I'm not the only who is having a hell of a time finding my leak. I'll check that, and I need to finally add a catch can to the PCV valve side.

 

I feel ya Came close to using a BFH on the damn car ( jk )

PS i edited the post on how to test the valve. Mitsu's valve is the only brand I found of the three I tested that consistently holds shut under low to medium boost. That affects throttle response and drivability IMHO

 

I didn't read this whole thread... but...

If cyl 1 is at TDC.. this means cyl 1 is between the compression and power stroke if memory server. This also means cyl 4 is between the exhaust and intake stroke. There is valve overlap at TDC at this point when the exhaust is being expelled as the piston rises and the intake valves begin to open to let the charge air in.

 

Yes I just looked at a cam today thinking about it and there has to be overlap. So how are we supposed to test past the TB?

 

Overlap only occurs at TDC between exhaust and intake stroke.

If you put cyl1 90 degress after TDC then that would mean all pistons are 90 degress from TDC. Therefore no chance for overlap.

 

this is helpful, thanks crcain! So could you (or some else) post how to actually set the engine to the desired crank position? I'm guessing, take off valve cover, put in neutral, and rotate to desired position, etc. but how exactly do I rotate the engine and what do the marks have to look like when I'm at 90 deg from TDC in cyl 1?

 

The cams and cam gears spin at twice the speed as the crank. So if you line the cam gears up with their marks. And you want to spin the crank 90 degrees, then you want to spin the cam gears 180 degrees. So just spin the crank until the exhaust cam gear mark appears 180 degrees from where it was lined up with the mark. I would spin the crank by just giving the ignition key a quick shot without letting the car turn over.