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Old 03-06-2013, 02:27 PM   #1
TheHighestCrew
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Default boost fluctuating

Mods: currently stock have not installed any stage2 parts until i figure out this issue.
Recently: had Subaru do the gas leak fix because this winter I was getting the raw fuel smell. They said they had to replace some vacuum lines that were worn and they could not re-use.

Issue I am having is in 2nd, 3rd, 4th when I drive in boost I am getting fluctuating at about .075 - 0.1 mpa. The car pulls nicely until it hits this point. The boost kind of flutters back and forth as if the power is stalling for a second then stabilizes. At first when I felt it I thought I was having a boost spiking but upon reproducing it while watching the gauge it is not going much if any over .1 mpa. But the back and forth shudder is concerning me.

At first I thought maybe they did not replace the restrictor pill, but I checked it is in there. Could they possibly have tightened the WG arm? I don't see why that would be involved with fixing the leak on the fuel rail. Or maybe the BCS is on its way out? I have not adjusted the tune from stock. When I looked through the rom it appears that everything as far as boost targets and WGDC are stock.
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Old 03-06-2013, 05:18 PM   #2
Turd Nugget
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I am having this same problem, my car is bone stock and my symptoms are exactly as you are describing. I changed the plugs, air filter and seafoamed it through both vacuum lines and the fuel. My next step is to change the fuel filter (since I'm guessing it probably has never been done and its got 112k on it 02 wrx) and I am awaiting for some parts in the mail, when they show up i'm installing the catless up and downpipes, i'm hoping one of the cats is getting plugged up.
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Old 03-06-2013, 05:34 PM   #3
art@grimmspeed
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This is a common issue with the stock BCS. Upgrade to a 3 port and a tune and you will be good to go.
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Old 03-06-2013, 09:39 PM   #4
TheHighestCrew
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I was thinking the more I reproduce it, feels like the bcs not keeping up. One more thing to replace
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Old 03-07-2013, 02:51 PM   #5
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What is the spring pressure in the stock wastegate? Why does there even have to be this ****ty BCS? whats wrong with just taking it out of the loop along with this "pill" people are talking about and let the wastegate do its own job? Obiously the BCS can only raise boost from the stock wastegate setting, so whats wrong with ripping it out and running a MBC?
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Old 03-07-2013, 04:04 PM   #6
DabiDa
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I had this same issue in my 02 bugeye i had replaced all the lines pill etc turned out to be the EBCS..I picked one up for 20 bucks and hopefully will upgrade or sell the vehicle before the OEM one goes out.
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Old 03-07-2013, 04:59 PM   #7
TheHighestCrew
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I am going to get a 3 port and avoid any other issues. I will be forced to run WG pressure until I re-tune my car for the 3 port BCS anyhow. I am also grabbing an OMNI 3 bar sensor, and a GM open element IAT sensor to convert over to SD. I have been studying the Carberry rom since it came out and I finally feel comfortable enough with the math and different methodology to attempt the switch.

Turd- I wanna say that the WG spring is something like half of the stock boost pressure so maybe 7-8lbs. I am not positive on that so make sure to confirm.

I found some good quality 3.5mm Vac hose on amazon, I am going to re-do all the old lines that were not changed. Do ya'll think 5ft will be enough or should I get 10ft to change out the lines involved for boost control?
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Old 03-07-2013, 07:56 PM   #8
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Quote:
Originally Posted by Turd Nugget View Post
What is the spring pressure in the stock wastegate? Why does there even have to be this ****ty BCS? whats wrong with just taking it out of the loop along with this "pill" people are talking about and let the wastegate do its own job? Obiously the BCS can only raise boost from the stock wastegate setting, so whats wrong with ripping it out and running a MBC?


Dude just use the search it's soooooooooooo easy to find answers...

since I'm feeling generous

1.) The stock BCS does it's job, but it gets tired and full of crud. Thus, stops doing it's job as well. This may lead to fluctuating boost.

You can remove the stock BCS and clean the ports. By attaching a battery to the positive/negative terminals on the BCS, you will physically open the solenoid and be able to clean the entire port.

2.) The wastegate DOES do it's own job. But mechanical boost is only controlled up to 7psi. After that, the BCS dials the boost according to air/fuel/etc.

3.) MBC are cool on honda's, not on a Subaru
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Old 03-07-2013, 08:37 PM   #9
alx8283
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Recently, I had a similar issue. Fluctuating boost, then eventually over boost, fuel cut and a cel for the bcs. I checked the oem bcs for proper function and it was fine. It ended up being a split in the boost reference line right by the nipple on the turbo's compressor. I replaced that section of line and everything's a-ok
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Old 03-08-2013, 07:52 AM   #10
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Quote:
Originally Posted by greenplates View Post
Dude just use the search it's soooooooooooo easy to find answers...

since I'm feeling generous

1.) The stock BCS does it's job, but it gets tired and full of crud. Thus, stops doing it's job as well. This may lead to fluctuating boost.

You can remove the stock BCS and clean the ports. By attaching a battery to the positive/negative terminals on the BCS, you will physically open the solenoid and be able to clean the entire port.

2.) The wastegate DOES do it's own job. But mechanical boost is only controlled up to 7psi. After that, the BCS dials the boost according to air/fuel/etc.

3.) MBC are cool on honda's, not on a Subaru
Just sounds like some german engineering to me, a little overcomplicated for such a simple system.
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Old 03-08-2013, 08:24 AM   #11
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Ok, so I pulled out the BCS, put it on a dc power supply, pulsed it a bunch of times and it seems to be working normally. I blew in one side and pulsed it and air came out the other without restriction. I cleaned it anyway with some iso and stuck it back in. This car is 100% stock yet, so maybe next weekend i'll put in the up/downpipes and while I'm at it I'll inspect the wastegate area for cracks and make sure it is shut all the way. I'll report back. Sorry to thread jack but it doesnt seem right to make a new one for the same problem.
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Old 03-08-2013, 03:20 PM   #12
TheHighestCrew
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Quote:
Originally Posted by Turd Nugget View Post
Ok, so I pulled out the BCS, put it on a dc power supply, pulsed it a bunch of times and it seems to be working normally. I blew in one side and pulsed it and air came out the other without restriction. I cleaned it anyway with some iso and stuck it back in. This car is 100% stock yet, so maybe next weekend i'll put in the up/downpipes and while I'm at it I'll inspect the wastegate area for cracks and make sure it is shut all the way. I'll report back. Sorry to thread jack but it doesnt seem right to make a new one for the same problem.
sometimes even when cleaned the solenoid is just worn out.

How are you tuning for stg2? Opensource or AP? If you are looking for a relatively cheap upgrade to a 3 port here is what I ordered:
3 port MAC valve 35A-AAA-DDBA-1BA 32$ shipped from amazon:
Amazon.com: Mac 3 port solenoid boost controller air valve locker pwm: Everything ElseAmazon.com: Mac 3 port solenoid boost controller air valve locker pwm: Everything Else
this is a good quality solenoid that they use in the AEM kits. Just need to get a few fittings from the local hardware store. They should be less than 5$. Obviously a tune is required. It will hold boost above stock pressure unlike the 2 port stock BCS. There is a review on it in the reviews forum.
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Old 03-08-2013, 03:29 PM   #13
Turd Nugget
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Quote:
Originally Posted by TheHighestCrew View Post
sometimes even when cleaned the solenoid is just worn out.

How are you tuning for stg2? Opensource or AP? If you are looking for a relatively cheap upgrade to a 3 port here is what I ordered:
3 port MAC valve 35A-AAA-DDBA-1BA 32$ shipped from amazon:
Amazon.com: Mac 3 port solenoid boost controller air valve locker pwm: Everything Else
this is a good quality solenoid that they use in the AEM kits. Just need to get a few fittings from the local hardware store. They should be less than 5$. Obviously a tune is required. It will hold boost above stock pressure unlike the 2 port stock BCS. There is a review on it in the reviews forum.
I'm not going to do anything to the tune, there is no reason when just doing an exhaust. I have tuned dozens of cars myself and have all my own equipment for doing that, so if I ever do decide to change to a bigger turbo i'd just opensource it. If I do get rid of the BCS I will tear it out completely and use a MBC or EBC. This car is just an econobox winter beater for me, I never intended on modding it at all, but it feels like a complete pooch so I feel I should at least get it into tip top shape for what it is. Thanks for the help though. If getting rid of the cats doesnt solve my problem I'll post back.
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Old 03-09-2013, 08:50 PM   #14
greenplates
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Quote:
Originally Posted by Turd Nugget View Post
Ok, so I pulled out the BCS, put it on a dc power supply, pulsed it a bunch of times and it seems to be working normally. I blew in one side and pulsed it and air came out the other without restriction. I cleaned it anyway with some iso and stuck it back in. This car is 100% stock yet, so maybe next weekend i'll put in the up/downpipes and while I'm at it I'll inspect the wastegate area for cracks and make sure it is shut all the way. I'll report back. Sorry to thread jack but it doesnt seem right to make a new one for the same problem.
Ok so I have been through this same situation.

1. Replacing the stock BCS with a new one is always promising, they get old and worn out

2. Your vacuum lines dude? The ones year the turbo and the ones near the throttle body get old and cracked. THAT will cause boost fluctuation

3. Make sure your couplers on intercooler are tight


This takes less than 20 minutes, is free, and helps a lot
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Old 03-09-2013, 09:27 PM   #15
BrokenSilver777
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If you haven't gotten it taken care of yet take it back to the dealer and tell them to look at all of your gaskets that they even came remotely close to touching.
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Old 03-10-2013, 01:33 AM   #16
tjmmason93
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Quote:
Originally Posted by alx8283 View Post
Recently, I had a similar issue. Fluctuating boost, then eventually over boost, fuel cut and a cel for the bcs. I checked the oem bcs for proper function and it was fine. It ended up being a split in the boost reference line right by the nipple on the turbo's compressor. I replaced that section of line and everything's a-ok
How will you know if your over boosting?
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Old 03-10-2013, 12:27 PM   #17
Turd Nugget
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Quote:
Originally Posted by greenplates View Post
Ok so I have been through this same situation.

1. Replacing the stock BCS with a new one is always promising, they get old and worn out

2. Your vacuum lines dude? The ones year the turbo and the ones near the throttle body get old and cracked. THAT will cause boost fluctuation

3. Make sure your couplers on intercooler are tight


This takes less than 20 minutes, is free, and helps a lot
I took a close look at the vacuum lines, Impressively this car looks brand spanking new under the hood, all the hoses and lines even still have some shine to them, none of them feel hard at all. I had the intercooler off a few weeks ago when I seafoamed it and double checked all the couplers.

I looked at a handfull of these wrx's and as soon as I popped the hood on this one I was impressed at how clean it looked. Even the intercooler looks new, where as every other one I looked at has bent/corroded fins. After I bought the thing and put it up on jackstands to get a better look at everything I noticed overspray, the car was def repainted but I cannot find any signs of repaired dammage inside or out so maybe it was just hail dammage or something idk. I'm from wisconsin and its hard to find 10 yr old cars not rusted to ****, this one came from texas a year ago so that would explain why I suppose.
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