2008 Stock STi, low boost problem

phantomsr · 01-23-2014, 10:50 PM

It's been a long time since I've been here. I did a lot of mods and work on my 02 WRX in the past but I've chosen to keep my STi pretty much stock and I must say, it sure saves on the pocket book. Until now.

170,000KM on the car and I've noticed a decline in power and so I started doing a little self diagnosis where I can. My garage is no longer a fully equipped shop and right now, it's not even heated so I'm limited in what I can do until summer.

Anyway, as no one would be surprised, I pulled the downpipe and found a crack at the wastegate and some excessive play in the shaft. Not having the time or tools or place to tackle a turbo swap in -20C I took it to the dealership. They confirmed that was likely the cause and I gave them the go ahead for the swap. Once they pulled it off we found the blades on the compressor where quite worn on the ends so that just confirmed the issue even more. I considered upgrading but I don't do anything half way and if I swap the turbo, I would do all the supporting mods and not half ass it and that's just not in the budget, so stocker it is.

So they get it all back together and it's better but still low on boost and they decide it's likely the gaskets on the TGV's and quote me $700 to take a look and change them out. In for a penny, in for a pound so why not. I did suspect an intake leak and that isn't all that unlikely. The cost seemed a little high but it was all labor other than the gaskets, and I guess they need 5 hours to strip her down to the heads and reassemble. I'm pretty sure I had the engine out of my WRX and on a stand in about 6 so this seems a little high but whatever. Just do it.

So then I get a call that the TGV's need to be replaced. This is where I decide to go in and take a look for myself. They have the intake and TGV's off and on a bench next to the turbo. Turbo is exactly as expected but what I didn't understand is what this had to do with the TGV's. So what he shows me is that under pressure the tail end of the TGV shaft is open to the air under a little metal plate but not sealed off. Under mild pressure there is air leaking through the end of the shaft on both side. Can't say how many PSI he had as it was just from the airgun on hand. It wasn't a big leak but they said they can't repair it and need to replace both TGV assemblys.

So that's where my question comes in as I'm having a hard time thinking that leak is going to be large enough to substantiate a 1.5-2lb shortfall in boost. Has anyone else come across their TGV shaft leaking? I don't want to get into another $1200 in parts to find out that A) the new OEM does the same under the same unrealistic test situation, B) that turns out to not be the problem and up goes the total again.

TLDR: Stock TGV assembly, anyone had boost leaks from the shaft where it leaves the housing? Is this something that can be repaired or shall I just pick up a TGV delete and an AP and call it a day?

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Daynger · 12-27-2020, 10:46 PM

I was really hoping to see some replies on this one. I am having the same issue. I read somewhere else that some guys have used JB weld at the bottom of those plates to cover the holes and it solved the problem. But I am REALLY curious or the opinions on that. What was your finding on this issue???

Jay11STI · 12-29-2020, 08:32 AM

I have no experience with the TGV issue you are having.

Out of curiosity, has any other test been done on the car prior to replacing the turbo? For example, have you done a boost leak test and smoke test? Those two test will really help identify air leaks that can be robbing you of power and creating post MAF leaks.

Daynger · 12-29-2020, 08:01 PM

Yes I have. I have done a boost leak test. I have air coming out of the bottom of the small plates on each TGV located on the side. I will attach a pic. I have plugged them both with JB weld now. Car is running a lot better. Still not hitting my target boost though. I need to do another leak test. I might have an exhaust leak now or something. If I don’t find anything with those two options I will try replacing the boost solenoid maybe.

Seangraz · 01-03-2021, 03:00 PM

Check for any cracks or leaks on your headers and up pipe. I small exhaust leak before the turbo can have a big impact on boost.

01-23-2014, 10:50 PM	#1
phantomsr Scooby Newbie Member#: 69071 Join Date: Aug 2004 Location: Edmonton Vehicle: 2002 Stg2-WRX Wagon WRB & Dust	2008 Stock STi, low boost problem It's been a long time since I've been here. I did a lot of mods and work on my 02 WRX in the past but I've chosen to keep my STi pretty much stock and I must say, it sure saves on the pocket book. Until now. 170,000KM on the car and I've noticed a decline in power and so I started doing a little self diagnosis where I can. My garage is no longer a fully equipped shop and right now, it's not even heated so I'm limited in what I can do until summer. Anyway, as no one would be surprised, I pulled the downpipe and found a crack at the wastegate and some excessive play in the shaft. Not having the time or tools or place to tackle a turbo swap in -20C I took it to the dealership. They confirmed that was likely the cause and I gave them the go ahead for the swap. Once they pulled it off we found the blades on the compressor where quite worn on the ends so that just confirmed the issue even more. I considered upgrading but I don't do anything half way and if I swap the turbo, I would do all the supporting mods and not half ass it and that's just not in the budget, so stocker it is. So they get it all back together and it's better but still low on boost and they decide it's likely the gaskets on the TGV's and quote me $700 to take a look and change them out. In for a penny, in for a pound so why not. I did suspect an intake leak and that isn't all that unlikely. The cost seemed a little high but it was all labor other than the gaskets, and I guess they need 5 hours to strip her down to the heads and reassemble. I'm pretty sure I had the engine out of my WRX and on a stand in about 6 so this seems a little high but whatever. Just do it. So then I get a call that the TGV's need to be replaced. This is where I decide to go in and take a look for myself. They have the intake and TGV's off and on a bench next to the turbo. Turbo is exactly as expected but what I didn't understand is what this had to do with the TGV's. So what he shows me is that under pressure the tail end of the TGV shaft is open to the air under a little metal plate but not sealed off. Under mild pressure there is air leaking through the end of the shaft on both side. Can't say how many PSI he had as it was just from the airgun on hand. It wasn't a big leak but they said they can't repair it and need to replace both TGV assemblys. So that's where my question comes in as I'm having a hard time thinking that leak is going to be large enough to substantiate a 1.5-2lb shortfall in boost. Has anyone else come across their TGV shaft leaking? I don't want to get into another $1200 in parts to find out that A) the new OEM does the same under the same unrealistic test situation, B) that turns out to not be the problem and up goes the total again. TLDR: Stock TGV assembly, anyone had boost leaks from the shaft where it leaves the housing? Is this something that can be repaired or shall I just pick up a TGV delete and an AP and call it a day? * Registered users of the site do not see these ads.

12-27-2020, 10:46 PM	#2
Daynger Scooby Newbie Member#: 521251 Join Date: Dec 2020 Vehicle: 2011 Subaru STI Dark Blue	Dam I was really hoping to see some replies on this one. I am having the same issue. I read somewhere else that some guys have used JB weld at the bottom of those plates to cover the holes and it solved the problem. But I am REALLY curious or the opinions on that. What was your finding on this issue???

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12-29-2020, 08:32 AM	#3
Jay11STI Scooby Newbie Member#: 492422 Join Date: Oct 2018 Chapter/Region: Tri-State Location: North Jersey Vehicle: 2011 STI	I have no experience with the TGV issue you are having. Out of curiosity, has any other test been done on the car prior to replacing the turbo? For example, have you done a boost leak test and smoke test? Those two test will really help identify air leaks that can be robbing you of power and creating post MAF leaks.

12-29-2020, 08:01 PM	#4
Daynger Scooby Newbie Member#: 521251 Join Date: Dec 2020 Vehicle: 2011 Subaru STI Dark Blue	Yes I have. I have done a boost leak test. I have air coming out of the bottom of the small plates on each TGV located on the side. I will attach a pic. I have plugged them both with JB weld now. Car is running a lot better. Still not hitting my target boost though. I need to do another leak test. I might have an exhaust leak now or something. If I don’t find anything with those two options I will try replacing the boost solenoid maybe.

01-03-2021, 03:00 PM	#5
Seangraz Scooby Newbie Member#: 518909 Join Date: Sep 2020	Check for any cracks or leaks on your headers and up pipe. I small exhaust leak before the turbo can have a big impact on boost.