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Boost Control

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Hey everyone so I have a 2013 subaru impreza wrx usdm with the stock vf52 and stock wastegate. So I'm mid tune right now and I have been having some overboosting issues. So no matter what boost I hit I am having 0% wastegate duty cycle. I have cobb 3 port boost controller that is brand new and I have verified about 100x now my plumbing is correct and the boost controller is working properly. Also all line are brand new and no leaks I have done several smoke tests with no leaks. So today I decided to test mechanical boost of the wastegate which I believe on a vf52 should be around 8-10psi. So I did a 3rd gear pull at roughly 50-75% throttle and still hit 19 almost 20 psi of boost with 0% wastegate duty cycle no matter what So to mean this should mean the wastegate is faulty. If anyone could please shed some light on this I would be forever grateful. I plan to contact cobb tomorrow and see if they can give me any advice.


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Hey Michael,

Looking at the boost curve, it looks like the wastegate isn't flowing enough to bypass exhaust gases away from the turbine wheel

First thing I would do is check the wastegate operation by blowing some air with an air gun in the vacuum hose of the actuator, looking at the wastegate actuator to ensure it is moving freely. Try to go slowly so you don't damage the diaphram, anyway it should open with about 10 psi of air pressure. Then you could try to remove the boost controler solenoid and connect the turbo port to the wastegate directly and check the boost pressure.

I know that de-catting these engines can results in boost creep, but I don't think that it's the case with a catted downpipe. A solution to that is porting the wastegate hole to help it's flow.

So right now I am running mechanical spring pressure of the wastegate which I would think on a vf52 turbo wastegate should be around 8-10psi but I'm still overboosting to almost 20psi so this should confirm the wastegate is faulty correct? I have a oem style replacement coming here in a couple days but until then idk what else it could be? I have a line going from the compressor nipple to the wastegate nipple and still hitting almost 20 psi of boost at a little over 50-75% throttle so I feel it has to be a faulty wastegate. Does that make sense?

Sounds like you already bypassed the boost control solenoid so we can take that out of the equation. It could be the wastegate actuator not working properly, or it could be the flap inside the turbine housing getting stuck and not opening fully. Easy check to make sure the flap is moving freely is disconnecting the rod of the actuator and moving the flap by hand. It should move without effort.

Yes I have a single hose running from the compressor nipple to the wastegate nipple which should prevent the car from going over whatever the spring pressure would be I'm not sure exactly what that pressure is but I would think it wouldn't be more than 8-10 psi and still hitting 20psi of boost. I've disconnected the arm and the flapper moves freely I have a bellmouth downpipe so it shouldn't be hitting anything but no matter what I'm still overboosting with 0% wgdc. To me it has to be a faulty wastegate. I have even hooked regulated air to the wastegate and at 8-12 psi will not open until closer to 20psi..

Based on the info you've given us it does looks like a bad actuator. At least you did make some tests instead of shooting random parts at it, so good job to you for that!

So I know it should take some force to move the actuator arm but when I did have the arm connected to the flapper it took almost all my force with one hand to move it but it does move. So to me for some reason it seems the actuator arm some how is so still that it just can't open. Have you ever heard of this? Also just want to say that in my first two logs to my tuner I was getting some wgdc % response even at low rpms but then I did a 50% throttle pull had low wgdc numbers and then at the very end of the log it falls to zero and hasn't adjusted sense. To me it has to be a bad actuator idk what else it could be I've done all the tests cobb recommends for the boost controller and everything checked out according to there test. I just don't get it so frustrating!! Thank you again for all the advice I can't thank you enough.

I have a TD06 on an EJ25, and when i first started using it i had a similar issue. The wastegate in this case was actually moving, but was not able to flow enough air. So the excess air went through the turbine, which increased boost, which increased flow which overwhelmed the wastergate even more and so on. I was seeing over 20 PSI of boost at mid rpm levels, luckily the ECU decided this was bad before rodney chose to exit the engine.

To fix it, i pulled the turbo out, stripped it and got a die grinder and ported the wastegate opening. Just leave a bit more meat on the edge closest to the hinge to stop the flap binding up or catching the rim.

Also its important to look at the other side, as if you can also create a channel and lip on the inside of the housing to encourage more air to flow out the wastegate rather than through the turbine then this makes a big difference. I've attached my before and after photos to help

After i did the porting, its been stable on boost control with the OEM wastegate that came with the turbo and a normal 3 port boost controller. And 18PSI of boost is only taking around 60% duty cycle

Attached Files

So when you were having your issues were you experiencing 0% wastegate duty cycle no matter what? That is my issue right now and I can't proceed with my e tune till I get this resolved. Like I said before I even tried to run mechanical spring pressure only by bypassing the 3 port boost controller and connecting a single hose from the compressor housing nipple to the wastegate nipple and still was hitting like 20psi of boost with partial throttle and 0% wastegate duty cycle. I would think if mine was being overwhelmed I would still see some wgdc but unfortunately I'm not so I would think with that test would confirm the wastegate is bad?

OEM exhaust manifolds? If aftermarket they may be butchered with the opening from the manifold to the wastegate being too small to draw off the gas flow. I assume you've double checked all the lines are correctly placed, and there're no leaks or blockages from the hose damage?

Oem exhaust manifold and yes I did a very extensive smoke test last night from several different locations and no leaks also did a exhaust smoke test with the wastegate actuator arm disconnected so I could keep the wastegate flapper open freely and had a minor leak where the cobb downpipe connects to the mid pipe which I will be fixing tonight. The spring bolts that are on that were too short so I went ahead and got some better bolts for my application. But again no leaks on the oem manifold. Again I connected a single hose from the compressor nipple to the wastegate nipple so I could only run mechanical spring pressure and I still overboosted to 20 psi with partial throttle and 0% wastegate duty cycle no matter what So this should confirm its the wastegate correct?

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If you've bypassed the solenoid then it should run at the base pressure of the spring, unless the wastegate itself is either A stuck shut (or mostly shut) or B. it is opening but it is getting overwhelmed, by the sounds of your mechanical tests its the latter. And a wastegate duty cycle of 0 should in theory produce the same result as running it on spring pressure.

I think you have 2 issues. 1. is the wastegate is being overwhelmed. And you boost controller isn't working as even if the wastegate was playing up, you should see that initially the boost controller should log that its running some percentage of output at lower rpm and manifold pressure. Once it approaches your target boost, it should back off, and then once it exceeds i'd expect it eventually end up at 0% in a effort to rein in the climbing boost pressure, however its stuck at 0 suggesting its not even trying to work.

Right on...yea so I'm using a cobb 3 port boost controller that is brand new. So anyway one of my first tests was to actually verify the boost controller was working properly, so first I verified I was getting voltage from the connector on the engine harness and then tested continuity of the boost controller itself which fortunately those passed. So then I started doing some research and came across on Cobb's website and found a test there which I will a link a picture of below but it passed as well. So really my only assumption would be the wastegate either ruptured the diaphragm or maybe the spring broke which I know are both rare. I'm just not sure I'm making enough power to be overwhelming the wastegate flapper itself idk.. I would just think hitting almost triple the mechanical spring pressure around 20-21psi boost when I'm like 95% sure it's a 7psi spring it's just oem so I wouldn't think it would be much.

Also I can't get my wastegate duty cycle to move period it stays at 0% no matter what. When I first started my tuning and made my first two datalogs I was atleast getting some sort of wgdc% even at low rpm almost no boost and the I did a 50% pull 2500-6000rpm and I was over boosting with low wgdc but still with some sort of wgdc reading so after that is when all this started so idk if something happened with that pull or what...?

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Let's rewind a bit here.

You have a stock engine, a stock turbo (VF52), a stock wastegate actuator. You have a catted COBB GESI downpipe. The boost controller isn't connected (it's bypassed as you are running a vacuum hose from the compressor nipple to the wastergate), so it doesn't matter if the WGDC is at 0% or 50% or 100% right now. I can't explain why your WGDC is at 0% except if you zeroed out the duty cycle tables in the tune. But again, right now it doesn't matter.

I said in my first post that removing restriction from the exhaust system can result in boost creep, and porting the wastegate hole is the solution to this. Obviously I would suggest you remove the downpipe and do like Paul suggested, it will only be beneficial!

Then you said this : "I have even hooked regulated air to the wastegate and at 8-12 psi will not open until closer to 20psi".

If the wastegate flap isn't opening at 8-12 PSI, it won't flow, obviously. When you connected the turbo to the wastegate, did you use the OEM hose with the restrictor pill installed? If you did, I would suggest you swap it for a new generic vacuum hose without the restrictor pill just in case it's clogged and you aren't getting the proper boost reference to the wastegate.

Finally, you keep saying it's happening at 50-75% throttle, but looking at your log, the throttle is opened at 90% closing to 85%. You are indeed applying 50% accelerator pedal, but the ECU is opening the throttle at 90%, based on the torque request and target throttle position tables. Just keep that in mind!

Side comment, boost solenoids are designed to be fail safe.

So thats why in the diagram you attached, if it looses voltage its 12V feed (or receives no signal) then it basically is the same as connecting the vacuum line from the wastegate to the outlet of the turbine (bypassing the solenoid)

Otherwise, if it worked the other way, then if you had a wiring issue, it would cause boost to go through the roof. Whereas this way, it drops to the wastegate spring pressure.

With you waste gate further to Francis point above. Check your wastergate actuator arm alignment. These on most subaru's and turbo's have a little kink in the arm and its designed to allow you to align the arm correctly so that it moves horizontally in line with the pivot point on the turbo wastegate flapper.

I did make the mistake once, were i hadn't aligned this right, and had slightly over tightened it. When the wastegate tried to actuate, is was pushing the arm at a slight angle, and was jamming. As a result in my case it took several more PSI of pressure on the wastegate to essentially force it to move and overcome the jamming.

I've attached an image of what i mean, the arm should be aligned like in the image in the direction of the blue arrow

Attached Files
  • IHI-VF52-Subaru-Turbocharger-side-Pro-Systems-Turbo.jpg
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

That's normal behavior for the parts combination you have.

That engine and turbo with an upgraded intake and exhaust will boost creep. It will be worse when cold outside, or in higher gears, but the issue is present as long as you have that parts configuration since the stock turbo wastegate flow is inadequate once you improve the intake and exhaust parts as you have.

Here's an article that will hopefully explain, and offers some solutions.


The thing is though since I am running wastegate spring pressure only by connecting a single hose between the wastegate and compressor housing and I am still overboosting wouldn't that confirm that the wastegate is faulty? I just got a replacement in the mail today so we will see if this fixes it but everything I've researched has said if I am still overboosting on spring pressure only the it has to be a faulty wastegate...

If you read the article I provided all will be explained.

The wastegate design of that stock turbo is adequate for a stock vehicle, but not one with upgraded intake and exhaust.

Changing the actuator doesn't change the physical flow of the housing and flapper.

Even with the wastegate arm disconnected so the flapper is wide open that turbo will boost creep.

Great article Mike, very well explained

Thanks Frank!

So I put a new oem style wastegate on and still looks like I'm overboosting. My tuner I believe has the wastegate set to 0% and he insists this is not boost creep. He is a qualified cobb pro tuner and other than this the car has been running great. I've double checked the boost controller again, smoke tested intake and exhaust system, tested the boost controller harness on the engine harness everything passes. I know all you guys keep saying this is boost creep but wouldn't it be leveling it momentarily at mechanical boost and then creep? My most recent log which I will attach from this morning it just looks like it's not even trying to control the boost...I'm just so frustrated I don't know what else to do...money is tight for me right now and I just can't go external I'm trying to troubleshoot absolutely everything before porting the internal wastegate cuz I'm just not sure it is boost creep wit this specific situation. My powe numbers are pretty low right now and I've even tried putting the oem boost controller back on(yes with the restrictor pill) and still overboosts and even on wastegate pressure only with a brand new wastegate...I would greatly appreciate anymore advice.

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Have you tried completely removing the spring?

I'm not sure what you mean by removing the spring completely?


Your log is exactly what boost creep looks like on the engine/turbo you have. This isn't a wastegate actuator problem or a boost solenoid issue.

It makes spring pressure of about 9 psi at 3000, creeps to 10-11 psi around 4000 RPM, then where airflow really takes off boost creeps much worse, then up top boost tapers some because that turbo can only flow so much air.

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I just don't understand why my tuner would be telling me otherwise then? I know everybody is different with experience and all that. So do you think if I ported the wastegate path it would help me out at all? I mean my tuner is pretty reputable he has completed all of the hp academy courses he is a certified pro tuner by cobb but I guess in this instance he must be incorrect because I have literally troubleshooted everything I can...or maybe would putting the oem downpipe back on? I really can't mess with the cold air intake cuz I have a fmic..

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