Boost problem?
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This is a discussion on Boost problem? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; New here and new to owning a subaru and turbo car. Now my question is what should my boost be? ...

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    Boost problem?

    New here and new to owning a subaru and turbo car. Now my question is what should my boost be?
    My upgrades are;
    Full exhaust borla
    Perrin intake
    Aftermarket blow off and gauge
    And not sure anything else but maybe intercooler

    I don't look down a lot but it seems like my boost is staying around 5-7 psi
    Not hard on it but not easy. Sometimes I feel like there is a loss of power in 4-5 gear on highway.

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    Subaru Newb MainFrame's Avatar
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    What model of car do you have, and what year is it? What kind of engine management are your running, and what is the boost target? Have the vacuum lines dealing with the boost control system been messed with at all, and what condition are they in?

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    Are you sure the gauge reads psi and not mpa? What year is the car?

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    Try reseting your ECU. Mine had a similar problem and it turned out it was in "limp" mode. Took me forever to figure it out. Just unplug the battery, pump the brake a few times and wait a few minutes before reconnecting.

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    Quote Originally Posted by Barefootdan View Post
    Try reseting your ECU. Mine had a similar problem and it turned out it was in "limp" mode. Took me forever to figure it out. Just unplug the battery, pump the brake a few times and wait a few minutes before reconnecting.
    If the ECU has lowered boost it was for a reason. Resetting the ECU doesn't magically fix the problem.
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    sorry i have a 08 wrx premium. I have some pictures to help with the understanding.Click image for larger version. 

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    This photo the wire above the alternator is cut. Can someone tell me what that is?

    Click image for larger version. 

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    I am to to sure what that controller thing does.. You can see it in the photo 2 hoses go into the controller and the other photo shows how its connected.

    Click image for larger version. 

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    This shows how the bov is connected

    Any help would be great. Im going to try to reset the ecu soon

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    Sammich Makin' Pwincess wrxtreme06's Avatar
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    is the car tuned?

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    Apparently is had the cobb access port but he kept it.

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    Subaru Newb MainFrame's Avatar
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    The only reason to keep it would be if he unmarried it from the car to sell. If it has been unmarried then the car has the stock map back on it. Seeing that it has a MBC installed, I would assume that it is not safe to drive the car until you get it properly tuned.. driving the car on a map that is not dialed in to the mods your car is running can quickly destroy the engine.

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    Quote Originally Posted by Donkey View Post
    If the ECU has lowered boost it was for a reason. Resetting the ECU doesn't magically fix the problem.
    From the looks of it, that's an MBC... the ECU has no control over the boost whatsoever! I'd hazard a guess that the plumbing on that MBC is not correct or the MBC is backed out all the way forcing the turbo to run mechanical boost. Either way you MUST get the car tuned for the mods that are installed. Hopefully the PO unmarried the AP before removing it.
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    I really have to do this? If so who should I go with?

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    Subaru Newb MainFrame's Avatar
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    Quote Originally Posted by Fusionf21 View Post
    I really have to do this? If so who should I go with?


    I can't see it in the pictures, but if you still have the OEM BCS you could potentially hook it back up like it's designed to go and install a stage two OTS map, but I don't know of any that are designed to run with the Perrin intake (TP probably has one you could buy). With the unknown condition of the car, I would take it to a reputable Subaru shop and have them look it over to see what else is going on with it, then get it tuned.


    We will need to know your location to be able to recommend a shop in your area.

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    I'm from north jersey.

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    I don't see why I would need a tune for just the little things done for it. I don't know much about subaru so I'm not arguing but I am mechanically inclined. I see to get full performance out of the mods yea I do need one but why would the car be in danger if I don't? Someone clarify that for me.

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    Subaru Newb MainFrame's Avatar
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    Any of those parts by themselves will require a tune on your car (intake, downpipe, MBC).


    With an aftermarket intake your MAF readings are likely to be skewed. If more air is entering the engine than the MAF sensor is reading it causes a lean condition. Running lean not only causes excessive heat that could potentially melt a piston, it is also one of the main causes of knock. Engine knock can not only crack a ringland (which is very common), it can also destroy rod bearings. A spun bearing basically ruins the entire engine because not only does it gouge the crankshaft and seize the engine, it sends chunks of metal through the rest of the engine clogging oil passages, gouging other bearings and cams, etc. A cracked ringland basically causes one cylinder to have no compression, you lose all power, and the engine dies. I would assume running on three cylinders will cause spun bearings as well.

    An aftermarket downpipe changes boost dynamics drastically. The turbo can spool earlier, more freely, etc. This unexpected increase in air from the turbo causes a lean condition and can also cause the engine to experience excessive cylinder pressures (especially if you're experiencing uncontrolled boost spike, which has to be tuned out). Same thing with lean mixture goes here, broken ring lands, fried bearings, etc. Additionally, excessive cylinder pressure is known to crack cylinder walls and can snap rods. A broken rod usually punches a hole through the side of the block, draining all the oil out along with gouging the cylinder wall beyond recovery. A cracked cylinder wall allows oil to get into the coolant and vice verse. You do not want coolant in your oil. In a short time the reduced ability to lubricate the engine will cause excessive wear on all moving parts and you will spin a rod bearing in no time.

    Running a MBC that's not tuned for is just ridiculous. The ECU has no control and no idea what the turbo is doing. Super rich and/or lean conditions are almost surely going to be present, along with a host of other issues. Basically, you're asking for a broken ringland, spun bearing, blown turbo, etc.


    Each thing by itself could easily destroy the entire engine in a short amount of time if the ECU is not properly adjusted. All three together is just asking for a $8000 repair bill.

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