Boost Spiking and releasing?

Hey LGT.com,

 

Newbie to Boxer engines and subarus here...

 

I picked up a 2008 LGT spec B a week or so ago, experiencing a little problem.

 

The boost is spiking @ around 15 psi and quickly releasing, multiple times very quickly. I'm not talking about plain ole' boost tapering off toward redline, it does it multiple time per gear, on WOT. Is the the dreaded "hesitation/studder" I've been hearing alot, and how do I fix it?

 

I noticed that the line ran to the boost gauge (from previous owner) is pretty much flat... causing an issue maybe? I may try to record this occurrence today.

 

UPDATE: The real issue is that the car is overboosting, usually by 2-3 PSI. The stock tune was seeing this and Turbodynamics was pulling the boost back just to have it build up again. The stock EBCS has been replaced and now the real culprit may be wastegate/actuator.

 

Thanks for everybody who has helped me so far.

check all the hoses under the hood, check for leaks and popped off lines.

What mods has the car received? Has a tube been applied?

 

This is purely a guess based on what little information we have... but...

Your turbo is supposed to max at around 13psi (stock). If for some reason it is producing more than that, the wastegate would open to compensate. Maybe it's opening to relieve pressure, closing to build boost, opening to relieve pressure, etc. Could be a bad tune, could be a lot of things... need more info.

What mods has the car received? Has a tube been applied?

 

This is purely a guess based on what little information we have... but...

Your turbo is supposed to max at around 13psi (stock). If for some reason it is producing more than that, the wastegate would open to compensate. Maybe it's opening to relieve pressure, closing to build boost, opening to relieve pressure, etc. Could be a bad tune, could be a lot of things... need more info.

 

The car has a k+n intake, stock tune AFAIK. Boost gauge installed as well. Looking to buy a stock intake because i know all about how these effect mildly modded subaru's.

check forrrrr leaks or loose hose clampsssss

Yeah I would recommend looking for popped hoses. My car popped a hose not too long after going stage 2. If your car produces 15psi, that's more than stock, and you might have a popped hose. (you might pop a hose with stock pressure for all I know)

 

Here's a link to the hose I had to reconnect:

http://legacygt.com/forums/showthread.php/boost-leak-hissing-noise-160128.html

I won't be able to see that without pulling the intercooler will I? Didn't see a single leak or anything...

http://s160.photobucket.com/albums/t193/vdlion717/?action=view&current=IMG_0850.mp4

 

Here is a video I recorded earlier today of what is going on... was in 3rd gear. WOT

 

pic of line to boost gauge, flat.

 

http://i160.photobucket.com/albums/t193/vdlion717/IMG_0851.jpg

Correct, you need to remove the intercooler, which takes about 5 minutes...

 

That definitely looks bizarre... Do hear any hissing, sucking, or other suspicious sounds?

http://i160.photobucket.com/albums/t193/vdlion717/IMG_0853.jpgpics of whole engine bay for shits and giggles... Seeing if anybody spots anything odd.

 

http://i160.photobucket.com/albums/t193/vdlion717/IMG_0854.jpg

is that a braided avcs oil delivery line?

 

http://i160.photobucket.com/albums/t193/vdlion717/IMG_0851.jpg

 

 

That hose right there is too far off the barb IMO. Push it back on, and put a zip tie around the two ends. Then, check all the other hoses (under IC), under alternator, etc etc).

if you have a hose loose, you will spike but then boost will steady at wastegate...about 6 or 7psi. when my bpv hose was d/c under the ic it would prematurely release boost because the bpv would release without backpressure from the line

^^ I had the exact same experience. Boost was capped out way low, and then a CEL came on about 5 minutes later.

 

OP, has the car ALWAYS exhibited this behavior? (since you bought it, I mean) Or is this something that cropped up after the purchase?

okay i'll tighten things up tomorrow... no issue with the boost line, don't think it's supposed to be flat and crimped like that...

being flat would make sense since at idle and low rpm you have vaccum in the line. I would replace the line with a more rigid one.

Tightened those lines up and zip-tied them... made no difference. Still doing exactly what it does in the video I posted.

did you take off the intercooler to check the hoses underneath?

nope, not yet. I assume that is to check the T that you referred to above? I may do it in the morning.

Search all the hoses, every single one in the engine bay and tell us what you find

Also make sure that the BOV isn't sticking. You need to remove it and check.

 

But also skip the flattened hose going to the gauge for a while since it can interfere. You shall probably connect the gauge to some other place on the manifold instead to avoid strange effects.

 

The line you have to the BOV may have some dampening restrictors to avoid "rattle" and vibration from the pulsating air in the manifold to propagate to the devices and the added volume of the hose to the gauge may cause oscillation problems - especially since it contracts and expands all the time.

Dunno why nobody suggested it yet... I'm going to take the car to subaru and have on of my buddies do the dealer reflash for "hesistation while hard accelleration". Otherwise known as the studder problem. Here's to hoping it fixes my issue.

you have an intake without a tune, it woouldn't surprise me if you are pulling timing on the stock tune with the addition of collaborative lean condition.

you have an intake without a tune, it woouldn't surprise me if you are pulling timing on the stock tune with the addition of collaborative lean condition.

 

In the process of buying the stock intake+snorkel off a user here... I don't like the typhoon intake anyway... I'll go stage 2 and If I go with a BNR turbo down the line I'll prolly get a Cobb intake.

 

I originally thought the boost releasing could be causing the car to studder but now that I think about it, my symptons almost exactly mimic what everybody experiences with the "studder under hard accelaration". The one that Subaru has a reflash for. Seems to me like the engine is just opening and closing throttle under WOT. Weird.

Dunno why nobody suggested it yet... I'm going to take the car to subaru and have on of my buddies do the dealer reflash for "hesistation while hard accelleration". Otherwise known as the studder problem. Here's to hoping it fixes my issue.

 

Let us know if that's the fix! In the future, please feel free to search the FAQs lol