acid7711

iTrader: (2)

Hey guys,

Yes, I know this topic has been covered a million times prior, but I'd like to get a straight answer as searching around has yielded mixed results from people saying it's safe to others cautioning against blowing seals, which is my main concern with this.



My Evo is tuned for SD, and it's been running great since it's last tune. Recently when it started to feel weird - letting off the gas while in gear won't cause the ECU to go lean (as it should), and it's kind of 'lurching' down low, and just generally feels a bit less smooth and more jittery.

Being on SD and seeing the car not lean out when letting off gas in gear is making me start to think I may have a vacuum/boost leak that is causing these issues, so I think my next step is to do a boost leak test and track down any issues and resolve those.




I've seen a lot of people just pressurizing right at the inlet of their turbo, but are there potential consequences of this? I mean, that side of the turbo is usually subjected to immense vacuum, not actual pressure. The last thing I want to do is blow a seal on a turbo that's been running fine, and I'm worried about doing so. Are there other potential issues to watch out for?


My understanding is, you need to remove the line that goes from the PCV to the intake manifold and block the part going back into the manifold, leaving the PCV on the head side open. I've also read it's important to make sure to remove the oil cap.

I do not want to damage my turbo or my engine doing this incorrectly and have read so many stories about people doing this incorrectly (albeit on other makes/models) and blowing/damaging seals or causing their engines to suddenly start burning oil/blowing smoke while running.


Thanks for any insight anyone can offer.

Biggiesacks

just don't use some crazy high pressure and you wont blow anything, except maybe the cap off the turbo inlet...thats always fun. I run 26-28psi of boost so i test @ 30psi. The turbo inlet is the right place to be capping off, you want the compressor housing to be joined in the test. If you are running a stockish pcv setup you don't want to block off anything, you want the pcv valve to also be tested. You want everything past the turbo inlet to be as close to how you would run the car as possible. If anything does leak then you fix it, thats what a boost leak test is for.

acid7711

iTrader: (2)

Okay, thanks for the reply. I'm pushing about the same boost levels, 26/27, so it's good to know you've safely tested it like that and at those pressures. I'll have to build up one of those caps with a stem on it and give it a go and hopefully not pop any seals or anything.

Still sketches me out, reading all these horror stories on the net.

LetsGetThisDone

iTrader: (1)

The turbo doesn't have "seals" to blow out. It uses a metal ring, similar to a piston ring, which works off of differential pressure to keep the oil in the CHRA.


Doing a boost leak test will not harm anything.

4G63_EVO

iTrader: (4)

I run 28-30 PSI and have tested up to about 32.

The only negative outcome ive had come from this is the car misses a bit on first startup, sounds like a subaru. One rev up and it goes away

acid7711

iTrader: (2)

That issue sprung up from doing a boost leak test?



The main reason I'm concerned is I had a buddy a few years ago who I watched do a boost leak test on his WRX. I watched them use a slow, regulated increase of air pressure and checked to ensure it didn't get crazy high, and ever since that boost leak test happened, his car always smoked after it. It happened right after it too, and I can attest to it not smoking before hand.

I'm not sure what happened, but he blew some kind of seal out while doing it. He did it right where the MAF was on them, and it couldn't have been more than 20-23psi. Ever since that day, I've been weary of boost leak tests, specifically for that reason. I guess I always assumed he somehow blew something in the turbo that caused it to push oil into the exhaust housing and burn it. The car didn't seem to run any differently. It just smoked a little, not a crazy amount, but something def wasn't right.

4b11slayer

I have a fp red amd when doing a boost leak test it blows oil.into exhaust.
Also you need to block off the pcv system side that goes into intake tube to hold pressure

acid7711

iTrader: (2)

It sounds like that's temporary though right? What I saw with the WRX was not some little bit of oil that just pushed past somewhere then quickly burned off. Something actually got damaged doing it.


Good to know about the PCV. I take it you just disconnect it form the intake tube side and cap that off, then leave the other side vented?

4b11slayer

Its enough oil to take a few miles to stop smoking lol.

Yea well ive never blocked off the actual pcv line. Maybe thats the real way to do it. Im no boost leak expert but thats what has worked for me.

acid7711

iTrader: (2)

Haha.

Appreciate the help man.

Biggiesacks

if you block off the pcv how will you know if the check valve leaks under pressure?

acid7711

iTrader: (2)

In my mind, it would be far safer to pull the valve off the engine and hook it up to a source of pressure to be tested manually, rather than risking accidentally pressurizing the crankcase.

That's how I would personally opt to check it.


I mean, honestly if you leave it hooked up, how are you gonna test to ensure it's leaking or not under pressure? It's not like you're going to feel or hear it when it's connected. It's a solid metal piece with a rattle-ball inside.

Biggiesacks

the engine has other breather ports, you wont be pressurizing the crankcase with the volume of air used in a boost leak test. If you open up the engine oil fill you will hear air leaking in if thats case and it will relieve even more pressure. You will also use soapy water where the hose goes over the pcv to see if its leaking from there too. In my mind what ever little rig you come up with to test the pcv off the car is far more likely to come flying apart and injure somebody then just testing it on the car. Don't get me wrong, if you have the time/resources and you want to come up with test rigs for what ever parts you want to test individually go for it. That's just not something that's commonly done AFAIK. How many evo threads have you found where someone damaged something doing a boost leak test? You don't blow out seals doing a boost leak test, you find bad ones and replace them, or thats how I look at it anyway.

acid7711

iTrader: (2)

Essentially, It's a solid metal tube with a metal BB that's a little bigger than the outlet, inside of it. Who needs a rig for this? If it doens't leak at 1psi of pressure, that means the metal BB is sealing. Adding additional pressure and force against the metal ball inside isn't going to cause it to leak any more. That'd be the same thing as expecting your foot to go through a concrete patch if you put more muscle into it. If it seals properly against a small amount of pressure, it's going to seal even better with a linear increase in pressure. Hold it in your hand and apply some pressure against the one side; why would it need to be any more complicated or elaborate than this? This isn't a semi-flexible hose that can expand like a balloon under pressure we're talking about here, although you are correct that the line leading to the valve itself could be a source of a leak, and thus does give merit to leaving it place and testing it on the vehicle with an open oil cap, which is again why I made mention in my initial post inquiring the importance of removing the oil cap during the test.



As I said, I have personally seen this cause something to become permanently damaged on an engine. Albeit, it was a boxer engine in a WRX, but a boost leak test is essentially the same regardless of what particular engine design it's conducted on.


The point of entry was the same; pre-turbo inlet, and it literally resulted in enough oil being constantly burned from somewhere at a steady enough rate to cause a noticeable amount of smoke being produced in either the engine or exhaust somewhere after. In my mind, that leaves either some kind of seal/bearing in the oil journals of the turbo, or an internal seal on the engine somewhere, which honestly didn't make much sense to me. I figured hot turbo + hot exhaust + leaking oil from damaged seal/band inside turbo = oil being burned inside the exhaust. That made the most logical sense to me, as damaging a seal by pressurizing the intake tract on an engine designed to run with positive pressure behind it didn't make much sense to me. The only thing that seemed different was forcibly applying a lot of pressure where there is normally an immense amount of vacuum and never any actual positive pressure.

In either case, it didn't smoke before the test was done, and it did after. IIRC, the PCV was left connected, the engine was literally bumped over a few times to get closer to TDC, MAF removed and replaced with the tester cap and stem, and the system was pressurized to 22psi. Obviously, something that was sealed and was previous retaining oil was no longer doing so after performing the test. I wouldn't have created this thread out of concern for my own engine had I not witnessed this happen with my own eyes.



Also, this post:
https://www.evolutionm.net/forums/ev...leak-test.html

Biggiesacks

this isnt a subaru, its a completely different engine layout. Countless members here do the boost leak test the same way, myself included, and have no problems. Maybe the subaru has some kind of design bug/feature that causes problems, i dunno never owned one.