Boost surge/BCS
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This is a discussion on Boost surge/BCS within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; First, I've probably read every thread on the internet related to boost surging and the boost control solenoid. Second, I'm ...

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    Boost surge/BCS

    First, I've probably read every thread on the internet related to boost surging and the boost control solenoid. Second, I'm new to more "advanced" car tinkering and I have only had my Subaru for about 2 weeks.

    I am having consistent boost surge in gears 3,4,5. The turbo will pull hard, let off, pull hard, let off. This happens from about 3500rpm to whenever I decide to shift or slow the hell down.

    I have NO mods. I have NO boost gauge.

    The previous owner swears it has to do with the BCS, so today I cleaned it out with MAF cleaner. While in there I noticed that the line coming out of the BCS and into the T fitting had a few cracks at the junction between it and the T fitting. I will attach pictures of that. So, I reinstalled the BCS and put some ****ty (but should have been airtight) tape around the cracks on the vacuum line (if that is the correct term). Needless to say, after taking the car out I didn't notice any improvement in the problem.

    So, I had someone turn my key while I listened for the BCS to click. I'm not sure if I was supposed to listen when the key was being turned to accessory mode or when the car was actually turning over. When turned to accessory mode I heard a click close by, but I don't think it was from the BCS. When the car was turned over it was too gd loud to notice a small click from a small part - at least it was for me.

    My plan is to buy a used BCS and swap it in the see if that fixes the problem.

    Would an admittedly ****ty tape job over the vacuum line be enough to prevent leakage at such high pressure? I will replace the line asap, but I didn't have the time tonight.

    After cleaning the BCS and taping the line should I have reset my ECU, or would it have automatically adjusted for the new found airflow?

    I checked all the lines into and around the BCS and immediate area visually and did not notice any issues. I'm going to do this again tomorrow, but I'm not sure exactly which lines should be checked. Assuming all of them..

    Is buying a used BCS ($30, no problem) a good place to start?
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  3. #2
    Good news, everyone! xxxxxxxAnub1s's Avatar
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    The fact that your boost is fluctuating at all shows that your BCS is working correctly, but swapping it out for another known good one would be a place to start at least. Replace ALL of those vaccuum lines when you get a chance. Tape doesn't gaurantee a seal, and besides it looks pretty ghetto.

    Reset your ECU and see what happens. I doubt it will be any better, but at the very least I would bet your ECU has learned some less than adventageous fueling and timing parameters and it would be good to clear those out.
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    Registered User teflon_jones's Avatar
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    What year and model is your car and how many miles on it?
    Scott
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    Oops. 02 wrx 99000 miles.

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    Registered User teflon_jones's Avatar
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    Yeah sounds like it's time to replace your vacuum hoses.
    Scott
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    I will give that a shot today and see how it goes. So, which lines need to be replaced?

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    Moderator Donkey's Avatar
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    I would first and foremost get a boost gauge. Did you install that vacuum T? By surge do you mean a boost spike or oscillating boost (up and down repeatedly)?
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    Up and down repeatedly. No I didn't install the t fitting. Def need a boost gauge.

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    Up and down repeatedly. No I didn't install the t fitting. Def need a boost gauge.

  11. #10
    Moderator Donkey's Avatar
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    Quote Originally Posted by maw230 View Post
    Up and down repeatedly. No I didn't install the t fitting. Def need a boost gauge.
    I don't think it's the BCS. Try adding slightly more preload on the wastegate arm. Maybe a 1/2 a turn at a time. If it gets worse then remove preload.

    Cure for wastegate flutter? - NASIOC
    Last edited by Donkey; 04-02-2011 at 08:04 AM.
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    Cool, will give that a try. I went to O'Reilly and got replacement hose, but it appears to be too loose to fit over the existing connections. However the only cracks I can find are in the end of one of them, and the ghetto tape job should be enough for a temporary test.. I will try adjusting the actuator arm and then reflash the ECU. Thanks.

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    Will I need to re attach the turbo heat shield before running the car or is it safe to leave it off? Temp's hovering around 70 today.

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    Registered User metaldahlberg's Avatar
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    You'll get some more heatsoak without it.
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    Ok, so I gave the actuator arm half a turn (clockwise), reset the ECU, but still noticed the boost surge. I gave it another half a turn without resetting the ECU, and I thought I noticed an improvement. The person riding with me couldn't even notice at all.

    Should I reset the ECU after each adjustment?

    I think it may have improved marginally...

  16. #15
    Moderator Donkey's Avatar
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    Reseting the ECU will just mask the problem as IAM is reset to 8 making wastegate boost only available (10psi). Once IAM starts to rise the ECU will then bring the BCS back into play and raise boost. So in short,no do not reset the ECU.
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