Stock Boost Fluctuation? (with pics)
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This is a discussion on Stock Boost Fluctuation? (with pics) within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hello! First off, I spent a while searching, but this problem seemed to be happening more with modded wrx's, barely ...

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    Registered User Johnny V's Avatar
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    Stock Boost Fluctuation? (with pics)

    Hello! First off, I spent a while searching, but this problem seemed to be happening more with modded wrx's, barely any stock ones. Therefore, I thought a well-detailed question with pics might be beneficial not only to myself, but for future searchers too.

    I just bought an 04 WRX Sedan that had an MBC on it and a Greddy catback. Nothing else seemed to have been touched. Upon reading, I found that MBC's are not a good idea for our cars due to the possibility of hitting full boost at partial throttle. Therefore, I decided to return the boost control to the stock solenoid. After reading up on the hose locations, etc, I finished removing the MBC and returning it to stock. I had to use new hoses (They appeared to be the same inner diameter as stock) since the previous owner had butchered the stock ones. I then only boosted .05 and realized the restrictor pill (orifice), was gone. I ordered a new one form Subaru and installed it today in the hose between the compressor and the "T" that splits the line to the wastegate acuator and boost solenoid (The location of the pill is shown by the yellow arrow). I used a 3/16" T fitting (pictured in red arrow), since I did not have any 1/8" fittings. The green arrow points to the only stock hose left, the one from the side of the boost solenoid to the top nipple on the intake.



    From there, I put a long hose from the T to the bottom of the boost solenoid. The reducer to go from 1/4" to 1/8" was missing, so I replaced it with a 1/4" to 3/16" reducer (pictured in light blue arrow).



    The other hose going into the side of the boost solenoid was stock and went to the intake nipple (pictured in green arrow). Funny thing here is that it was disconnected when I bought the car and the nipple on the intake was capped off. I removed that cap and replaced the hose onto the nipple.



    After all of this, I reset the ECU and took her for a spin. The boost goes to about .09/.1 and then drops to about .06, then back up. It oscillates like this through most of the pull and then seems to settle at .05 again. As far as I can tell, everything is hooked up properly, except for the fact that they are not stock hoses. I know I am also missing the inline coupler that goes in the line from the T to the solenoid, where alot of people do the 3/16" mod. There is no inline coupler since the hose goes uninterrupted from the T to the solenoid. I doubt it's a boost leak since my boost was stable before I replaced the restrictor pill, and even when the MBC was on. The hoses look bigger than the stock hose in the picture, but the inner diameter seems to be the same. What do you guys think?
    -2004 San Remo Red WRX Sedan-
    Blobeye Syndicate #24

    "Pain of Discipline or Pain of Regret..take your pick." ~ Notre Dame

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    First thing I would try after swiching hoses at solenoid around, if that doesn't work, would be putting in a 1/8 coupler into the hose going to FBC solenoid as it also acts as a sort of restrictor for evening out airflow...everything else "seems" right... But I can't remember for shure, but the hose from T to FBC solenoid goes into the side of solenoid not the bottom, and the hose from bottom of solenoid goes to the air intake.
    Last edited by wrxdrvr; 01-11-2007 at 01:27 PM.
    '02 WRX 4EAT, 311,000KMs/194,500Miles, Sold. Best car I ever had. '09 STi stage 1, hope this one will be good too...

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    Resident meany-rator 06wrx4me's Avatar
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    Put in your 3/16" or 1/8" restrictor where its supposed to be, reset the ecu and take it for a spin.
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    Registered User Johnny V's Avatar
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    Quote Originally Posted by wrxdrvr View Post
    But I can't remember for shure, but the hose from T to FBC solenoid goes into the side of solenoid not the bottom, and the hose from bottom of solenoid goes to the air intake.

    Yea, I just left it the way I found it, which may be wrong... I also wasn't sure where each hose went on the FBC solenoid. I will get myself an 1/8" inline fitting to put in the hose also. Hopefully it's one of, or both, of those issues. I heard that buying OEM replacement hoses is like $104, which I REALLY don't want to spend.
    -2004 San Remo Red WRX Sedan-
    Blobeye Syndicate #24

    "Pain of Discipline or Pain of Regret..take your pick." ~ Notre Dame

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    Registered User Johnny V's Avatar
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    UPDATE: The hose locations on the solenoid were correct, I was just looking at it wrong. That being said, I found myself an 1/8" inline coupler and put it where the stock one would have been on the hose from the T to the solenoid. Reset the ECU and wow, what a difference! Took her out for a test drive and the boost hit .08 on the stock gauge and held perfect. The first pull it wavered a teenie bit, but I think it leveled itself out after that because it holds boost steady now. My question is, .08 on the stock gauge is about 11.6 psi. I have read that stock boost levels are 13.5 psi. Am I still running low boost or is the .08 normal? The "T" fitting is still 3/16", but boost levels are steady now so I should be running stock numbers.
    -2004 San Remo Red WRX Sedan-
    Blobeye Syndicate #24

    "Pain of Discipline or Pain of Regret..take your pick." ~ Notre Dame

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    Registered User dcpatters's Avatar
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    How are you measuring boost? Should be a load on the engine. 1st or 2nd gear will not suffice.
    2008 Evo X GSR. Custom tuned, Works panel filter, Intercooler pipe upgrade, TBE.

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    I would change the T to 1/8" too, You should be able to get 13.5 stock In third with a pedal to metal run. 4th for shure...
    '02 WRX 4EAT, 311,000KMs/194,500Miles, Sold. Best car I ever had. '09 STi stage 1, hope this one will be good too...

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    Registered User Johnny V's Avatar
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    Im using the factory boost gauge and doing pulls in 2nd. I guess I should be doing them in 3rd. I thought 2nd would be adequate, but I guess not. I'll also change out the T to 1/8" and see what that does. I'm just afraid that it might restrict it too much with the 1/8" T. Is the stock T 1/8" or 3/16"?
    -2004 San Remo Red WRX Sedan-
    Blobeye Syndicate #24

    "Pain of Discipline or Pain of Regret..take your pick." ~ Notre Dame

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    Registered User dcpatters's Avatar
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    Quote Originally Posted by Johnny V View Post
    Im using the factory boost gauge and doing pulls in 2nd. I guess I should be doing them in 3rd. I thought 2nd would be adequate, but I guess not.
    You are probably there now. Check again in 3rd gear. If not, a swap in diameter should set you up back to stock boost.
    2008 Evo X GSR. Custom tuned, Works panel filter, Intercooler pipe upgrade, TBE.

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    Stock is probly a bit smaller ID than 1/8"...The more you restrict air that goes to the wastegate actuater the higher the boost can get. Because it will not have enough pressure fast enough to open the wastegate in time and then you will get major boost spikes, if the ID is too small. 1/8 should be close enough...
    '02 WRX 4EAT, 311,000KMs/194,500Miles, Sold. Best car I ever had. '09 STi stage 1, hope this one will be good too...

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    Registered User Johnny V's Avatar
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    Swapped in the 1/8" T, reset the ECU, and did a few 3rd and 4th gear pulls. The stock gauge still hits .08, with a TEENIE lean towards .09, but most of the time it hits and stays at .08. This is still no more than 12 psi. I don't get it. Could the solenoid be causing the low boost? Is there anyway to check it. This is frustrating.
    -2004 San Remo Red WRX Sedan-
    Blobeye Syndicate #24

    "Pain of Discipline or Pain of Regret..take your pick." ~ Notre Dame

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    Registered User dcpatters's Avatar
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    Give it a few days. See if the boost peaks higher then. By the way, where are you seeing 12 PSI, more or less? The stock turbo will run out of breath in the higher RPM range.
    2008 Evo X GSR. Custom tuned, Works panel filter, Intercooler pipe upgrade, TBE.

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    Registered User Johnny V's Avatar
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    I'm seeing .08 at around 4k rpms. I'll give it a few days. If the solenoid was bad, I wouldn't be holding boost as well as I am, would I? It just feels like I am so far from 13.5 psi that I can't not think that somethig is wrong.. Maybe I need to be more patient..I dunno
    -2004 San Remo Red WRX Sedan-
    Blobeye Syndicate #24

    "Pain of Discipline or Pain of Regret..take your pick." ~ Notre Dame

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    Registered User dcpatters's Avatar
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    You are not that far. Do you have 93 octane in the tank? Try from 3000 RPM @ full throttle in 3rd gear and note the boost. Do the same in 4th. Consider using another gauge as well for reference. While you have definitely made the right changes, perhaps your gauge is slightly off. Definitely would not be the first time this has happened.
    2008 Evo X GSR. Custom tuned, Works panel filter, Intercooler pipe upgrade, TBE.

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    Registered User Johnny V's Avatar
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    Yea, I only run 93 on the car. I was thinking the gauge might be off. I want to get another boost gauge in the car, so I might have to do that sooner than later..
    -2004 San Remo Red WRX Sedan-
    Blobeye Syndicate #24

    "Pain of Discipline or Pain of Regret..take your pick." ~ Notre Dame

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