Losing boost...help?!?
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This is a discussion on Losing boost...help?!? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hey everyone, I tried finding a similar post on here but I'm new to this forum business so I'm still ...

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    Red face Losing boost...help?!?

    Hey everyone, I tried finding a similar post on here but I'm new to this forum business so I'm still learning. Anyway, here's the problem.

    My 02wrx is peaking at approx .05MPa or 7.25 pounds of boost...I don't know why. it is completely stock except for an injen cold air intake (previous owner installed). The boost gauge shows no problems in reaching 7.25, it isn't slow in peaking so i doubt it's a vacuum leak...but it stops dead there in any gear, at any rpm. Here's the catch...my boost used to be running solid, no problems whatsoever. A few weeks ago, it started acting up, it'd run full boost or decide on its own that 7.25 was enough...on several occassions, on long drives it would not function past the 7.25, however after shutting off my car and allowing it to sit for a while showed that upon starting again, that it would run full boost?... It makes no sense to me. Again, it's almost completely stock, it has never been tuned. I know the timing belt and water pump will be replaced this week or next week, as it just hit 100k miles, could this be related somehow? I dont hear any unusual noises when idling...i start hearing the hissing of the turbo when the guage creeps to 0.0 MPa, but never earlier...any suggestions on tests I can run to find a source of the problem? I read perhaps my boost solenoid could be bad, but I'm unfamiliar with how exactly turbochargers operate with the wastegate, solenoid, etc....I'm trying to read up on them to perhaps clue myself in and get *some insight...any help would be greatly appreciated. I am just trying to avoid the dealer as I'm pretty tight on budget

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    He simply abides. SD_GR's Avatar
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    Intermittent problem seems to imply a vacuum leak (?).
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    ClubWRX.net Vendor adam@kronosperformance's Avatar
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    Def sounds like a boost / vacuum leak my friend.

    Best thing for you to do is take off your top mount intercooler and start looking around for loose lines, holes in the intercooler hose (plastic tubes) and your turbo inlet for rips. Those are the common reasons for pressure drops and boost leaks.
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    How could it be a vacuum leak if it would come and go? (Forgive me if this sounds ignorant to me, I'm unfamiliar with the seeming complexities of a turbocharged system)

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    ClubWRX.net Vendor adam@kronosperformance's Avatar
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    Quote Originally Posted by offroadbiker16 View Post
    How could it be a vacuum leak if it would come and go? (Forgive me if this sounds ignorant to me, I'm unfamiliar with the seeming complexities of a turbocharged system)
    Sometimes items get loose and tight...so say for example, if your intercooler hose clamp is loosening and leaking air, sometimes it could be in a position to hold air and sometimes it may loosen to let air loose. Things like that happen. Boost leaks aren't always consistent.
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    If I could fix this without having to spend uber amounts of money that would be pretty awesome...considering I've been looking into a turboback and maybe an up pipe....without my turbo, where would i be? :P

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    It just seems strange that it has no problem peaking at 7.25, wouldn't a vacuum leak cause you to lose varying amounts of boost depending on the source of the problem? Why would it stop at precisely 7.25?

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    No idea lol
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    Alright, so yesterday evening after I got home I checked out some of the tubing (i.e. between wastegate, turbo and boost solenoid) and I heard no hissing noises, didn't see any cuts/abrasions on the tubing, and after reading somebody else's post (sorry..but on nasioc) there was no oily residue on anything either...(idk what his problem might have been). Anyway getting to the chase, so there didn't seem to be any obvious problems...but the car came with a boost gauge pre-installed in the dashboard. When at idle, the boost meter displays +(/-) -.06MPa, and while driving if I let off the throttle completely it shows (+/-) -.08MPa. When the car is shut off, the meter immediately goes back to the neutral/0MPa position...is this any clue that the problem may not be a boost leak? I feel if there was a leak, the boost meter would display a higher (less negative) number when cruising with no throttle while in gear...or even more so, when the car is shut off, I feel if there was a leak that the boost guage shouldn't reset to zero as there would be uneven pressure in the system. As soon as I get an opportunity I'm going to try removing my tmic if its necessary...but does anybody have any ideas? Logically (to me..and I am not too familiar with turbo systems) there should be a leak as I can reach .04MPa of boost, but nothing more...also..does anybody know what pressure the wastegate actuator is calibrated to?

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    (As a side note, I have not seen any check engine lights yet, but logically it seems as though it is my solenoid or a leak between the solenoid and the turbo...if anybody could please shed some light it would be greatly appreciated!)

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    Quote Originally Posted by offroadbiker16 View Post
    (As a side note, I have not seen any check engine lights yet, but logically it seems as though it is my solenoid or a leak between the solenoid and the turbo...if anybody could please shed some light it would be greatly appreciated!)
    If you search "low boost" on any subaru forum you will see the general consensus is of 3 main issues with the restrictor pill intact: * Boost leak *bad BCS ECU *defaulting to wastegate boost to due detonation The wastegate actuator can be set between 7-10psi on the 02 WRX. If you search "boost leak" on here or NASIOC you can easily find how to make a DIY tool and the instruction how to use it. For the BCS if you connect the green diagnostic plugs under the dash on the drivers side and turn the power on you should hear it cycle on and off along with the radiator fans. The ECU limiting boost unfortunately requires a SSM interface (Taxtrix cable/Cobb AP) to read the IAM/DAM to determine if detonation is the issue. You need to be running 91 octane as a bare minimum and 93/94 if available.
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    if boost leak, bad solenoid, or the ecu controlling for knock are factors, here are my thoughts (and questions)

    1. boost leak
    it seems likely since the needle on my guage seems to spool fine above 3,000 rpms, any rpm higher/any gear. it resets to 0 when the car is turned off, and registers at -.08MPa when in gear without throttle (always been that way). I didn't hear any noises when i had the car running and listening under the hood but then again I wasn't running boost so idk if i should have. but i feel this is the most likely option but not hearing any whistling makes me nervous that perhaps it isn't. any suggestions to this end?

    2. bad solenoid
    doesn't seem as likely but is possible, i will try connecting the green wires and starting the car while listening for the solenoid to kick in
    3. ecu limiting boost
    seems also possible, i always run premium so im not sure why the ecu would limit anything now, but i don't know much about it so if you have any info that'd be cool. i was running on low coolant for a while and i didnt realize it, after putting in coolant and allowing the car to settle my turbo worked full boost (this happened maybe a month ago). but perhaps if the ecu is involved, would disconnecting my battery for a while to reset the car show that and reset boost monitoring in the process?

    Thanks so much everybody btw for all your help! I wish i knew more so perhaps i could answer some questions for other ppl too haha this is a good community.sure as hell beats all those punks in lowered jetta's and gti's strolling around my town (although with my limited boost i had a jetta pulling against me today... :/ )

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    Also, if boost leak were the problem...i have two questions:

    1. Would I hear whistling from any of the tubes going to/from the turbo
    2. Besides the tubes going to the wastegate/solenoid etc. where would be a place i should check for a leak?

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    Hey dude...so I figured out my dilemma and thought it best to share with the community. Please hold your laughs because this was just a lack of maintenance that created my problem. The fact that my boost would work intermittently made me think it couldn't be a leak and it turned out that I was right. It was an electronic problem...well...so i tried diagnostic mode, but heard no solenoid clicking...so i started the car again, and had my friend rev the car to 3000 while i pressed my fingers to the housing of the solenoid. Thankfully, i could feel the rapid "ticking" of the solenoid activating. So no leak, no solenoid...but upon going back into regular (non-diagnostic) mode, my car wouldn't start...hadn't had that problem before...but had some corrosion on the positive battery terminal. Turned out, the corrosion actually ate away enough of the terminal to reduce the amount of voltage reaching my solenoid. Two dollars and twenty minutes later I had 14 lbs of boost and a new battery terminal. Thanks for all the help guys, i appreciate you all trying to give direction but it seems my crappy lack of basic maintenance in this case trumped...this will not be repeated that's for sure..

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