low boost - 6psi or so?

So I figured I am out of my break in period and started pushing the car a little - it only hits 6psi boost in pretty much every gear - gets right up there, then just holds... any thoughts as to what could be wrong? that's wastegate pressure, right?

I'm guessing it's the boost control solenoid is either disconnected or stuck closed. I'll take a look in the morning. ugh.

I'm guessing it's the boost control solenoid is either disconnected or stuck closed. I'll take a look in the morning. ugh.

 

I would guess it's the wastegate solenoid or solenoid vacuum/boost line routing. It could also be a massive boost leak.

I am thinking if it was a leak there would be all kinds of warning lights, and the car may not even idle or run properly. So if it's a leak it has to be a leak that doesn't allow air to be drawn back in under low pressure or vacuum. Check the TB coupler as well for tightness.

Could also be due to a blocked catalytic converter.

I was thinking the same thing for a leak - I should hear it whistling or something - the car was boosting quickly to 6psi then stopping - no rough idle, no drama, etc. - just wouldn't boost past 6psi, which is what I believe the wastegate spring is tensioned to. (a clogged converter would make it hard for the car as the rpm goes up, but it didn't feel like it was bogging or anything)

 

 

The wastegate solenoid seems fine - no flow unpowered, clicks open and then there is unrestricted flow - wasn't sticking or anything (tried rapidly clicking it open and it worked fine). The line from the solenoid to the T by the turbo (the one that's wrapped with the foil thermal insulation) seemed to be pinched off and stuffed up past the oil cooler - I pulled that mess out - verified none of the lines had any leaks, buttoned it back up, and the car seems to be boosting normally (well - normal for it being 100 degrees out and late in the afternoon...) so I think that was the problem - the insulation seems to have hardened up a bit - the line itself seemed fine (I had a line on my wrx that hardened then broke in the same position) - I might replace the line since the insulation is a mess and was definitely not very compliant.

 

Symptoms were consistent with the boost control solenoid being disconnected or stuck closed, and having the tube pinched accomplishes the same thing - when it opens, it's applied vacuum what amounts to a dead leg, so the wastegate opens when the pressure exceeds the spring force - 6psi or so.

and it's back.... won't boost over 6 or 7psi in any gear - only done pulls in first through 3rd (too much traffic around...) - so normal for 1-2, but should be higher for 3-6, right? looked at the line, and I hadn't put it back into it's holder on the intake to the turbo, so put it back there (that was a pain) - maybe it's pinched? I dunno. really, really, really annoying. no codes, no rough idle, no drama - boost zips right up to 6psi and sits there. verified via a second boost gauge (well, using my bluetooth obd2 and torque displaying boost pressure - it's saying I hit 7 or 8psi in each gear.)

 

 

 

really getting annoyed with this car. nothing else is amiss - fuel trims are low (around zero short and long term) nothing messed up as far as I can tell. maybe this evening I'll get out when I don't have cars in the way and try again. I don't get it.

I could be not paying close enough attention to the rpm... from this thread:

https://legacygt.com/forums/showthread.php/2012-stock-map-boost-target-208699.html

 

 

looks like it holds at around 6psi from 2900 to 3700 rpm... it's hard to do 3rd gear pulls when there's traffic... stupid weekend drivers! I'll wait until this evening and try again.

Edited June 29, 2019 by DrD123

Question for you.

Can you grab photos of the turbo area and vacuum lines?

 

 

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I can get under there and snap shots of whatever - what do you want to see? the t which has one leg going to the bcs, one going to the the turbo, and one to the wategate actuator? there's really not a lot to see down there!

So from what I’m gathering, you got the motor rebuilt?

You’ve replaced the vacuum lines on the turbo?

Doesn’t seem right. Stock gate pressure should be 8psi.

 

 

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short block was replaced in April (spun bearing) by Subaru, the vacuum lines to the turbo are original, from the computer it's 7.6-8 psi in 1 and 2 (boost gauge is reading what looks like 6 or 7) - also, be mindful that I am at altitude (6000 ft) and it's hot!

Can you see the wastegate duty cycle in torque? It could very well be an issue with plumbing, but I'm curious if the ecu is "disabling" or significantly reducing the duty cycle on the bcs for some reason. It should set a code before it goes all the way to spring pressure, but could be an easy check. If that looks ok, I'd give the bcs connector a jiggle to check for loose connection/broken wires.

 

 

Now that I re-read your post, how were you testing your bcs? In my experience, the boost->WG route should be open when unpowered, and closed when powered. I'm not sure if that's how our's work, but from a calibration perspective, if the solenoid fails, you want that path to be open so you don't make full boost all the time. The duty cycle should also tell you if its working backwards.

Torque is pretty limited in terms of what you can see (compared to an AP or other subaru-specific tools) - I can see the normal OBD2 parameters, graph them, and all that good stuff - so manifold pressure, fuel trims, O2 sensors, etc. - but nothing like wastegate duty cycle, commanded boost level, etc.

 

 

I tested the BCS by removing it from the intake - I was powering it directly from the battery while blowing through it (trying to see if it was sticking or something like that, which would have required cleaning - it's in a pretty clean section of the intake, so there's no real reason for it to get fouled, but figured I'd look!) - the BCS should open when the car is trying to build boost greater than the spring pressure, so it should normally be closed.

Ok - read a post on NASIOC where they had the restrictor pill on the wrong side of the t and had similar symptoms, but verified mine is on the compressor side, so the tubing all looks fine. thought maybe a boost leak, so verified all the clamps were tight (the ones to the throttle body went a few turns on either end) - drove it, and same deal - wastegate boost as a max in all gears.

 

 

Only thing I did differently when I got it to work properly before was to actually disconnect the BCS (then reconnect it when I was done) and pull the negative battery cable which would have reset everything - did that and boost was normal in third for a few minutes, then reverted back to maxing at wategate boost... thought maybe the knock sensor was loose, but it looks to be on there just fine. I don't get it. I thought maybe it was the gas, but it was doing it yesterday morning, I filled up yesterday afternoon (was on empty) and it's still doing it (I use Chevron - different station this time than last time, too...)

 

 

no idea what could be causing the car to not boost - it seems electrical - I am guessing maybe it's knocking like crazy, but I would get a misfire code if that were the case, right? I don't hear anything odd - the car doesn't bog or otherwise act funny. there are no codes, no flashing cel indicating a misfire, nothing.

 

 

I can't think of what else to check. The only thing that yielded a positive result was disconnecting the battery, but then it's a short lived fix, so there must be some learned value that's getting out of whack.

Simply weird.

No correction or codes. Sounds like a leak, but if it isnt. There only one true spot that can cause issues.

 

Check your bpv/bov.

Verify everything is connected, remove bpv and make sure it’s working properly.

Make sure during removal/installation that the valve seat position is facing the charge pipe and not the inlet side.

 

 

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Well, what I don't understand is why resetting the ECU makes a difference - if it were the BOV, that's a purely mechanical system, right? I wouldn't think resetting the ECU would have an impact on that. (I have a turbosmart kompact plumb back sitting on the shelf in my office waiting for install... ) - there's a thread over on NASIOC that's almost the same issue as mine - they saw it show up after having the airbag recall done. Oddly enough, I had that done about a week after the short block was replaced... they use some sort of wedge that pushes down on the floor - I wonder if it messed up the ECU? (there was definitely an impression on the carpet after they were done) - I'm going to give them a call tomorrow and see if I can get it looked at. everything was fine when I brought it in for the spun bearing - boost was normal, etc.

Resetting the ECU would reset your DAM to .812, assuming something made it drop, but I'm not sure that affects anything other than timing. Could be that there's some other learned value that's getting cleared as well, or maybe the ECU pulls boost as well as timing if DAM drops low enough.

from what I have read, when the DAM goes below 0.4, the car goes into "limp" mode and won't boost beyond wastegate boost. It's at the dealership now, so we'll see what they are able to find out. Other than not boosting, there are no other issues for me to chase, or clues to follow, so we'll see what they say. over on NASIOC there's a guy with an STi that said his started doing the same thing after the airbag recall - maybe something got damaged at that point that's making the car glitch? hopefully it's something simple and I have my car back tomorrow!

Any chance you filled up on gas right around the time you started pushing it a little harder? There's a chance it could be something as simple as bad gas.

Bad gas is certainly a possibility - I had the issue on Friday, though, and then filled the tank on Saturday and it was still doing it Monday. I got gas at two different Chevron stations, and 15 days apart (I don't drive a whole lot), so the odds of it being bad gas are low, I think. The dealer had no answers today, but it sounded like while they said they were going to look in the morning, they did not... hopefully some info tomorrow.

Did you ever check the TB coupler?

He’ll probably say he did and then go back to the resetting the ecu fixed the issues and saying that isn’t the issue.

Looking forward to the issue honestly

 

 

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He’ll probably say he did and then go back to the resetting the ecu fixed the issues and saying that isn’t the issue.

Seriously?

 

 

Couple of posts up I pointed out that I looked for boost leaks, tightening the clamps on both ends of the coupler between the intercooler and throttle body. Also checked the other clamps along the intake track. There are no leaks I can find.

 

 

Just got a call from the service manager at the dealer - the tech is going to call me - everything they have checked has turned out to be just fine. They also pulled the carpet and looked at the ECU and saw no damage to the cables going to it or to the connectors. It still does the same thing - reset it and it's all good, then it goes into limp mode. they also said there was a software update of some sort which they did, but that didn't fix anything.

 

 

If it were a problem with a coil or a plug, I would think the car would misfire, but it's not doing that. I am wondering if there isn't a loose cable or pinched wire somewhere that's giving electrical noise that's being interpreted as knock or something like that... if they throw in the hat and give me the car back, I guess my next step will be to trace the wiring from the knock sensor back to the ECU and see if there is anything messed up...

Seriously?

 

 

Couple of posts up I pointed out that I looked for boost leaks, tightening the clamps on both ends of the coupler between the intercooler and throttle body. Also checked the other clamps along the intake track. There are no leaks I can find.

 

 

Just got a call from the service manager at the dealer - the tech is going to call me - everything they have checked has turned out to be just fine. They also pulled the carpet and looked at the ECU and saw no damage to the cables going to it or to the connectors. It still does the same thing - reset it and it's all good, then it goes into limp mode. they also said there was a software update of some sort which they did, but that didn't fix anything.

 

 

If it were a problem with a coil or a plug, I would think the car would misfire, but it's not doing that. I am wondering if there isn't a loose cable or pinched wire somewhere that's giving electrical noise that's being interpreted as knock or something like that... if they throw in the hat and give me the car back, I guess my next step will be to trace the wiring from the knock sensor back to the ECU and see if there is anything messed up...

 

 

 

Doesnt matter about the throttle body coupling being tight. It’s a known fact they leak due to the design of them.

Replace that with a aftermarket one to be safe and from future headache.

 

Second thing, your tmic could of separated as well, also a known issue.

 

Third thing, intake manifold o rings are known to be a issue of the past. Verify with soapy water. Check the charge pipe o ring as well.

 

Or just simply have it smoke tested versus asking us here and shooting down every opinion that is given to you.

 

Don’t mean to be a a-hole here, but we’re simply trying to help you out.

 

 

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