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This is a discussion on ~Underboosting/\Explicit content~ within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Here's my situation. Car: 2005 Wrx STi Modifications: Cobb stage 1 93 Octane As we all know the STi comes ...

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    Registered User Black X Dahlia's Avatar
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    ~Underboosting/\Explicit content~

    Here's my situation.

    Car: 2005 Wrx STi
    Modifications: Cobb stage 1 93 Octane

    As we all know the STi comes factory with 14.5psi, and we also all know that Cobb Stage 1 increases this number to 16.5psi (+/- .5). My car is currently making 8.8 max psi. First thing that came to mind was boost leak, so today i ordered a boost pressure tester to perform a test. BUT....if i had a leak then the MAF would not catch it, therefore, I would be running rich, which i find i AM NOT, after reading my A/F Ratio's at idle and WOT. So i do some more thinking/researching and come across some info about my car coming factory with a manual boost controller. Basically the wastegate valve is opened some for less boost and closed some for more boost and when the wastegate actuator is fully open, the vehicle will run mechanical boost pressure which can be anything from 7-11psi. So i put 2&2 together, I'm not running rich so it couldnt be a leak, and im making 8.8 max psi with the correct fuel consumption, as if the wastegate was opened by the previous owner of the car, explaining how it could run so low of boost and the ECU correctly respond. BUT ONE PROBLEM.... all IHI turbochargers have a fixed wastegate actuator rod that cannot be adjusted. Meaning the previous owner could not have "manually" opened the wastegate to make it run mechanical boost at 8.8psi.

    So this leads me to ask a few more questions....

    1. Does the Wrx OR STi come with the factory manual boost controller? OR both?

    2. If so, then why do i see alot of ppl on the site (Wrx & STi owners) attempting to buy aftermarket manual boost controllers?

    3. Are STi owners buying aftermarket manual boost controllers to compensate for the fixed wastegate actuator rod?

    4. If an STi has a manual boost controller from the factory, why does it not have an adjustable wastegate rod?

    5. Does the wastegate need to be adjusted via Engine Management if it has a fixed wastegate actuator rod?

    Im still going to run the leak test when my pressure tester comes in, although im confident this is not my problem.

    If the leak test results show no leak, then the only thing i can think of would be to purchase an adjustable wastegate, if possible.

    Any takers?
    !EDIT!
    First i want to state the fact that earlier i mentioned that my car was not running rich. So i went out and ran it again watching my a/f ratio's, boost, etc... and cruising my ratio's are looking good at high 14's, but when WOT my ratio is at 11.1. This could be a LITTLE on the rich side, but i think the Cobb stage1 causes this 11.1 ratio.

    So this brings 2 current outcomes to the table

    1. I do have a boost leak, and when im at WOT it begins loosing pressure and therefore giving me the slightly rich 11.1 ratio.

    2. It is the Cobb stage 1 map giving me the ratio, and im back to wastegate possibilities.

    I would also like to add the fact that when in Neutral im reading anywheres from 10-11psi, and like i said earlier 8.8psi when WOT; Reading from the A/P live data screen.

    Once again, any takers?
    Last edited by Black X Dahlia; 10-05-2008 at 09:10 PM.
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    Here are target A/F ratios from the cobb website for 04-05 stage 1 STi

    Target A/F Ratios are mid 12's under load before the onset of boost. Under full load
    by 4000 RPM the A/F Ratio should drop to mid 11:1 and gradually run richer as RPM
    increase ending at high 10:1 A/F at redline.

    so looks like your runnin good.

    I would check vaccum lines from your turbo for and cracks or holes and check all the clamps on your intercooler hoses. Also check your intercooler hose for any cracks or holes mainly where the clamps are. Check your intercooler for cracks or leaks.

    and last Cobb says "If after 1-2 weeks worth of driving you are still unable to reach target boost
    pressures; you may try using the HWG version of this map."

    More from cobb about your map-
    Target peak boost pressure is approximately 16.5psi +/- 0.5psi depending on vehicle
    and conditions. Boost will likely taper to ~14.5psi by redline to increase
    reliability.
    Last edited by Bnowell4ver; 10-05-2008 at 09:42 PM.

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    Also I know the wastegate on stock 02 wrx turbo allows for 8 psi when the boost solenoid is not hooked up or there is a leak in the vaccum lines goin to the boost solenoid. Not sure what its set at on STi's tho.

    You can go to Subaru and buy a whole new set of vaccum lines. But it costs about 60 bucks for everything including all the plastic connections. So cheap bet is to find the leak and replace that one hose. I have heard of smoke tests where they can check for leaks, not really sure about them never had one done.

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    Master Baiter EJ257's Avatar
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    Are AFRs being read with a wideband? If not, get readings from a wideband ...
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    Moderator Donkey's Avatar
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    No your car does not come with a manual boost controller.Are you kidding me?The MBC would control the wastegate actuator.A MBC does not = an adjustable wastegate actuator. What have you done to the car recently and do you have a CEL/DTC?Little info for you....
    How Subaru’s Factory Boost Control System Works - COBB Forums

    Also,like idipskoalmint said,the factory A/F sensor is NOT a true wideband.It cannot read under 11.25:1 and is not very acurate outside of stoichiometric.The farther it get from stoich,the less accurate it is.I have logged my LC-1 against the factory sensor to confirm this as many others have.
    Last edited by Donkey; 10-06-2008 at 06:07 AM.
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    Registered User Black X Dahlia's Avatar
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    Quote Originally Posted by Donkey View Post
    No your car does not come with a manual boost controller.Are you kidding me?The MBC would control the wastegate actuator.A MBC does not = an adjustable wastegate actuator. What have you done to the car recently and do you have a CEL/DTC?Little info for you....
    How Subaru’s Factory Boost Control System Works - COBB Forums

    Also,like idipskoalmint said,the factory A/F sensor is NOT a true wideband.It cannot read under 11.25:1 and is not very acurate outside of stoichiometric.The farther it get from stoich,the less accurate it is.I have logged my LC-1 against the factory sensor to confirm this as many others have.
    The only thing done to my car is Cobb Stage 1. Im running 8.8psi in 4th (max psi), and should be running around 16.5. I've read that page on Cobb already, i didnt mean to type "manual" boost controller. Seems some ppl are focusing on the wrong subjects, lol. In that page it says that when the wastegate is all the way open, the car runs on mechanical boost which is anywhere from 7-11psi. I was wondering if the guy who had the car before me had somehow opened the wastegate to set the psi at such a low level, because if it was a leak, then wouldnt i be running pretty darn rich if i was loosing an entire 8psi by leak? Now if the guy who had the car b4 me did open the wastegate, then that would explain why im not running as rich as expected, because the MAF catches it and rearranges the correct fuel map for the 8 lbs of boost. Plus if you look at the cobb website on maps for stage 1 93 octane, they show the tested car running right at 11.1 a/f ratio WOT, which is what im running. Im going to untune the a/p and see what my WOT ratio looks like.

    It's either a leak or wastegate, I'll just have to wait and find out when the pressure tester comes in, and i'll post an update.

    thx for all the posts, you are all highly appreciated
    Last edited by Black X Dahlia; 10-06-2008 at 07:52 PM.
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    Your solenoid working properly? I was only running 9PSI with a bad one ...
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    Registered User Black X Dahlia's Avatar
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    Quote Originally Posted by idipskoalmint View Post
    Your solenoid working properly? I was only running 9PSI with a bad one ...
    good idea, is there anyway i can test the solenoid to see if it's bad?
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    Quote Originally Posted by Black X Dahlia View Post
    The only thing done to my car is Cobb Stage 1. Im running 8.8psi in 4th (max psi), and should be running around 16.5. I've read that page on Cobb already, i didnt mean to type "manual" boost controller. Seems some ppl are focusing on the wrong subjects, lol. In that page it says that when the wastegate is all the way open, the car runs on mechanical boost which is anywhere from 7-11psi. I was wondering if the guy who had the car before me had somehow opened the wastegate to set the psi
    People are just focusing on what you type.Obviously knowing the proper terminology helps when you describe a problem.There is the wastegate(which is part of the turbine housing),the wastegate actuator,and the wastegate solenoid.The car runs mechanical boost when the wastegate solenoid is all the way closed.This means the wastegate actuator is controling the boost pressure by opening the wastegate,which can be replicated by just running a vacuum line directly from the compresor housing to the wastegate actuator.


    Wastegate Solenoid Valve
    - An electromagnetic solenoid which controls the air flow from the wastegate actuator to the turbo inlet. This device is normally closed when no voltage is applied. When 12V direct current (DC) voltage is applied, by the drivers in the electronic control module (ECM), to the wastegate solenoid valve, it fully opens allowing air to pass through the device. A 0% Wastegate Duty Cycle (WGDC) setting will allow the solenoid to stay fully closed; which will force the turbo to run mechanical boost pressure. A 100% WGDC setting will force the solenoid to stay fully open; which will force the turbo to run maximum boost pressure






    Quote Originally Posted by Black X Dahlia View Post
    Plus if you look at the cobb website on maps for stage 1 93 octane, they show the tested car running right at 11.1 a/f ratio WOT, which is what im running. Im going to untune the a/p and see what my WOT ratio looks like.

    UUhm,okay.Do you have an aftermarket wideband 02 sensor,like a LC-1,or not?If not,there is no way you can aquire accurate AFR data.Cobb doesn't use the stock AFR sensor to tune their products.They use a dynometer and a wideband O2 sensor.Just want to make sure you understand the difference between the stock sensors and a wideband because I don't think you do....
    Last edited by Donkey; 10-07-2008 at 04:01 PM.
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    Registered User Black X Dahlia's Avatar
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    Quote Originally Posted by Donkey View Post
    People are just focusing on what you type.Obviously knowing the proper terminology helps when you describe a propblem.The car runs mechanical boost when the wastegate solenoid is all the way open.Which can be replicated by just runing a vacuum line directly from the compresor housing to the wastegate actuator.



    UUhm,okay.Do you have an aftermarket wideband 02 sensor,like a LC-1,or not?If not,there is no way you can aquire accurate AFR data.Cobb doesn't use the stock AFR sensor to tune their products.They use a dynometer and a wideband O2 sensor.Just wan to make sure you understand the difference between the stock sensors and a wideband because I don't think you do....
    yes i do, and yes i am.....................
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    Moderator timber's Avatar
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    Quote Originally Posted by idipskoalmint View Post
    Your solenoid working properly? I was only running 9PSI with a bad one ...

    +1 on the solenoid.
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    Moderator timber's Avatar
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    Quote Originally Posted by Black X Dahlia View Post
    good idea, is there anyway i can test the solenoid to see if it's bad?
    pull out the old one, and put a known good one in.
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    Registered User Black X Dahlia's Avatar
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    Quote Originally Posted by Donkey View Post
    People are just focusing on what you type.Obviously knowing the proper terminology helps when you describe a problem.The car runs mechanical boost when the wastegate solenoid is all the way open.Which can be replicated by just running a vacuum line directly from the compresor housing to the wastegate actuator.



    UUhm,okay.Do you have an aftermarket wideband 02 sensor,like a LC-1,or not?If not,there is no way you can aquire accurate AFR data.Cobb doesn't use the stock AFR sensor to tune their products.They use a dynometer and a wideband O2 sensor.Just want to make sure you understand the difference between the stock sensors and a wideband because I don't think you do....
    I see I see.

    Hmm i just thought of something. When your WG duty is at 0%, your solenoid valve stays fully closed, causing you to run mechanical boost. And a WG Duty setting of 100% will force the solenoid to stay fully open, and in turn run maximum boost pressure. Meaning if my solenoid was bad, then i would be running 0% WG Duty right? My WG Duty is at 75%, meaning the wastegate possibly being the problem is possibly out the door?
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    Quote Originally Posted by Black X Dahlia View Post
    I see I see.

    Hmm i just thought of something. When your WG duty is at 0%, your solenoid valve stays fully closed, causing you to run mechanical boost. And a WG Duty setting of 100% will force the solenoid to stay fully open, and in turn run maximum boost pressure. Meaning if my solenoid was bad, then i would be running 0% WG Duty right? My WG Duty is at 75%, meaning the wastegate possibly being the problem is possibly out the door?
    If your solenoid valve is stuck closed it doesn't matter what voltage your ECU is throwing at it. I think you would get a high duty cycle because your not hitting target boost, so it tries to open the solenoid more. I'm a bit surprised it isn't higher though.
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    Moderator Donkey's Avatar
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    Quote Originally Posted by Black X Dahlia View Post
    yes i do, and yes i am.....................
    I'm asking because I have seen in other posts you telling people about reading your AFR's using the Cobb AP V2.If your using the Cobb AP to read AFR's your not using a wideband.

    turbo question for car set up.
    Last edited by Donkey; 10-07-2008 at 06:45 PM.
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