Boost fluctuation/surge.
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This is a discussion on Boost fluctuation/surge. within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hello, I have a stock 2002 WRX with 138,000 miles on it, and I have just recently noticed that the ...

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    Boost fluctuation/surge.

    Hello,
    I have a stock 2002 WRX with 138,000 miles on it, and I have just recently noticed that the boost when I floor it will build to about .1 MPa and then drop to .05 MPa and then build back up to .1, and then drop again to .05. I have tested it in second, third and fourth gears and it does it in all of them. As soon as it builds to .1 it drops and rebuilds. I can also feel it in the acceleration. I do not know how long it has been doing this, as it is my commuter car and I rarely ever even hit boost at all.
    I have done a search on the subject and all of the threads are either modified WRXs or similar problems but not the same. Either way, there are no definitive answers in any of those threads. I have also tried to reference a few other sources and have not come up with anything conclusive. Can anyone help me out with this? Thanks.

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    Registered User justin.jordan2's Avatar
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    i would check the boost solenoid, the wastegate valve, but to me it seems like you have a boost leak, check all hoses after the turbo and into the intercooler, also check the bov,,
    COBB FLASHED STAGE 2, UPPIPE, DOWNPIPE WITH HIGH FLOW CAT, AND FULL 3 INCH CAT BACK, 160 CRUCIAL RACING THERMOSTAT, K&N FILTER. TRACK: 1/4 MILE 13.66 102.7 MPH ON THE COBB OTS MAP

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    Did a little more testing on my drive to class today at partial throttle. If I allow boost to build to .1 quickly, it will drop down to about .06-.07 MPa. Anything above .05 MPa will not hold boost, but below that is fine.

    Seems like a boost leak? Would that be normal with a boost leak for it to hold boost at lower pressures and not at higher ones?

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    Well I did a little research on the lead you gave me about boost leak, and it seems that is the most probable cause for the fluctuations. The way I figure it, it will hold boost at lower pressures but the gap opens at higher pressures. The part that is confusing the hell out of me is why it is able to repeatedly build full boost?

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    Moderator Donkey's Avatar
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    I would agree with the diagnosis of the BCS as well.Try cleaning it out with some electrical cleaner.
    Resident Adviser @ WTF Tuning, LLC
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    BCS huh, ok will do.

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    I broke two of the hoses when pulling that thing out, not the one with the restrictor pill in it, but the other two coming from that T connection. Son of a b*tch! If I went and just got some hose of the same diameter and cut it to size can I just use that? It's not special in any way is it?

    Anyway, I have to work tonight so I don't think I'll be getting to cleaning the BCS out, but when I do where should I spray the cleaner?

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    I had the same problem with I put my down pipe on. I had to adjust the waste hate arm. Has that been messed with? Mine was too tight and did the same Thing you are describing.i had to adjust it again when I flashed to stg2. I would give you a link to how to do that but I'm on my blackberry and that is a little difficult. So if anyone can help him out.
    open source stg 2, up/dp cbe, aem cai

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    Registered User teflon_jones's Avatar
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    Quote Originally Posted by samb View Post
    I broke two of the hoses when pulling that thing out, not the one with the restrictor pill in it, but the other two coming from that T connection. Son of a b*tch! If I went and just got some hose of the same diameter and cut it to size can I just use that? It's not special in any way is it?
    You just need to get tubing with the same wall strength, which you can measure pretty easily if a bit inaccurately by squeezing it in your hand. As long as it's as strong or stronger, you should be fine. Any tubing you buy should have a recommended operating temp stamped on it too so make sure you get something with a temp range similar to the stock hose.
    Scott
    Past Subies - '11 STI Limited stage 1+ and '04 STi stage 2+
    '13 Wrangler Rubicon - custom front bumper w/12k lb winch & off-road lights, skid plates, diff guards, etc.
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    Hm, it's going to be really tough to judge that by comparing because the hoses that were on there are hard and brittle as hell, that's why they snapped. I'm going to the hardware store tomorrow to see what I can find..

    As soon as I get that back together I'm going to go out and test out the changes you guys have suggested, and I will report back when I'm done. Hopefully we will have solved it.

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    Registered User teflon_jones's Avatar
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    Quote Originally Posted by samb View Post
    Hm, it's going to be really tough to judge that by comparing because the hoses that were on there are hard and brittle as hell, that's why they snapped. I'm going to the hardware store tomorrow to see what I can find..

    As soon as I get that back together I'm going to go out and test out the changes you guys have suggested, and I will report back when I'm done. Hopefully we will have solved it.
    Go to your local auto parts store and get some tubing, normally they'll have something that should work. Basically you just need to make sure it's not going to collapse or burst.
    Scott
    Past Subies - '11 STI Limited stage 1+ and '04 STi stage 2+
    '13 Wrangler Rubicon - custom front bumper w/12k lb winch & off-road lights, skid plates, diff guards, etc.
    '04 Porsche 911 Turbo GT2 clone 600 HP/TQ
    '77 F-150 heavily modded for off-roading

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    Registered User justin.jordan2's Avatar
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    kraigens has rolls and rolls of tubing that you can choose from. thats where i got mine.
    COBB FLASHED STAGE 2, UPPIPE, DOWNPIPE WITH HIGH FLOW CAT, AND FULL 3 INCH CAT BACK, 160 CRUCIAL RACING THERMOSTAT, K&N FILTER. TRACK: 1/4 MILE 13.66 102.7 MPH ON THE COBB OTS MAP

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    Ok guys, I replaced the T-fitting hoses with brand new ones, and made sure the connections were good. I also tightened down the hose between the turbo->intercooler, and the intercooler->throttle body. The problem went away!... For one second to third gear pull. The next pull it fluctuated slightly, maybe 3psi. And the one after that it was back to full oscillation.

    I am 90% sure that it is one of those hoses on the intercooler coming loose and leaking, so I plan on replacing them. Any suggestions on what I should replace them with? OEM rubber ones? Are there any aftermarket metal ones that you guys would recommend?

    I am assuming that I will need to remove the TMIC to get at the turbo output hose, and to do so requires the BPV to be removed. Should I buy a new gasket for that as well?

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    Registered User justin.jordan2's Avatar
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    Quote Originally Posted by samb View Post
    Ok guys, I replaced the T-fitting hoses with brand new ones, and made sure the connections were good. I also tightened down the hose between the turbo->intercooler, and the intercooler->throttle body. The problem went away!... For one second to third gear pull. The next pull it fluctuated slightly, maybe 3psi. And the one after that it was back to full oscillation.

    I am 90% sure that it is one of those hoses on the intercooler coming loose and leaking, so I plan on replacing them. Any suggestions on what I should replace them with? OEM rubber ones? Are there any aftermarket metal ones that you guys would recommend?

    I am assuming that I will need to remove the TMIC to get at the turbo output hose, and to do so requires the BPV to be removed. Should I buy a new gasket for that as well?


    i would go with samco hoses that wat im gunna do when i get my bigger top mount intercooler. if ur planning on upgrading ur car thats wat i would do. also make sure ur bov is tight and its gasket is still good.
    COBB FLASHED STAGE 2, UPPIPE, DOWNPIPE WITH HIGH FLOW CAT, AND FULL 3 INCH CAT BACK, 160 CRUCIAL RACING THERMOSTAT, K&N FILTER. TRACK: 1/4 MILE 13.66 102.7 MPH ON THE COBB OTS MAP

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    Is that a reusable gasket??

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