JP '98 GT-B TT - Second Turbo occasionally doesn't boost

[Legacy GT-B]

Hi there, I'm kinda new to the Subaru scene. I finally got a chance to upgrade from my Nissan Bluebird to a JDM 1998 Subaru Legacy GT-B in January. Unfortunately, I haven't had money to get her an alarm, so she's been sitting in the driveway for the last four months, apart from a short drive every week. Pretty soon after I bought her, the check engine light started going on randomly, which I finally got the money for to get checked out two weeks ago. It turned out to just be the knock sensor, which I got replaced last week. All is fine with the car, except sometimes after the VOD boost feels lacking. When that happens, the primary turbo boosts just fine, VOD comes on, and it feels like the primary turbo is boosting is after that, instead of being knocked back in my seat it feels like a gentle push. Any ideas what could be causing the lack of boost?

[Robbks]

hundreds of ideas..

first, reset the ECU
http://www.mrtrally.com.au/performance/howresetecu.htm

because the car has probably gone into limp mode due to the bad knock sensor, the ECu will limit boost on the secondary turbo.

Next start with reading this...
http://www.veloce.pwp.blueyonder.co.uk/ ... opprt2.htm (http://www.veloce.pwp.blueyonder.co.uk/Twin%20Turbo%20Operation/ttopprt2.htm)
it will give you the majority of the info on how each part of the system operates

then, how to make your TT work properly...

-One by one, remove, inspect, clean and re-install or replace every vac line on the car
the vac lines tend to get clogged with oil deposits and this stops the system from working correctly.
Take care to look for restrictors in the lines.
the line that connects to the wastegate on the primary turbo has one, as does line #2 at the solenoid box. these are essential for proper operation of the system
-If any of the lines are perished, replace them.
-I use "Upper-Engine Cleaner" to do this with. throttle body cleaner can be used also

-Next is to remove the Black Box of Death (BBoD)/ solenoid box on the strut tower.
-one by one, clean out all the vac lines, inspect them, inspect the joiners/ tee-pieces for good condition
-also, remove the solenoids from the box and flush them out with cleaner aswell. remove the vent caps from them and clean them too.

after doing this, and checking everything is where it should be, test the actuators (Intercooler valve, wastegate, Exhaust Changeover Valve) by sucking/ blowing on the vacuum lines that operate them. they should be able to hold a vacuum if they are in good order.

next, locate the green diagnosis connectors up under the dash and connect them
turn the ignition to ON and you should hear all the solenoids clicking, the fans switching on and off and the actuators activating.

Finally, do an ECU reset
http://www.mrtrally.com.au/performance/howresetecu.htm
and see how it goes.

if the problem persists, then there may be other issues, but at least you know the vacuum/ solenoid system is in good order.

there are a few other modifications and changes that can be made to the vacuum system to bypass some of the actuators and some adjustment to the ECV rod that helps to minimise the VoD

[Legacy GT-B]

Shit, that's a lot of work just to make sure the solenoid system is working, guess it's the price of owning a twin turbo. If I'd known going in that it was that complicated, I would've just bought a Forester or saved up a bit more for a version 4 Legacy GT-B lol

Thanks for the info, though!

[Robbks]

Or do what i'm doing, convert it to single turbo......

[Reuben]

Single turbo sounds good :P

Also, does the car have a pod filter? If so, revert to a stock intake for the love of god! If not, hmmmmm.


And lastly, go say hi to the chaps over at clubsub.org.nz

[Legacy GT-B]

Nope, she doesn't have a pod filter as of yet, though I was planning on getting one at some stage. Apologies for lack of updates, I've only been using her as my daily driver for the last two months or so, blame it on me being a slack motherfucker. I've finally got some spare change to sink into my car, so I bought a new head unit last weekend. Turns out I need new speakers as well, some of the originals are blown. Anyways, I just need to sort the secondary stage boost sorted, which doesn't appear to be co-operating at all any more, it's more noise than power at all times now. Good thing Auckland traffic doesn't allow me to boost above 3.5 grand much, anyway. I'm torn between going to Winger Subaru to get the solenoids sorted or going to Fredco just down the road, any experience with either of them, anyone?

[Robbks]

DIY clean and flush of EVERYTHING vacuum and TT related first.
go to your local Subaru Spare Parts dealer and get a Can of Upper Engine Cleaner and clean them all with that.
including all the pipes across the manifold

[Reuben]

Noise, no boost, poor performance. Smacks of a blown secondary.

You have 2 options.

Go to winger greenlane, and say:
"Hi, I'm a clubsub newbie, they sent me here. I've got some secondary problems, can you please do a 2 min test drive to see what's up?"
OR
Go to Highbrook automotive, and say:
"Hi, I'm a clubsub newbie, they sent me here. I've got some secondary problems, can you please do a 2 min test drive to see what's up?"

Both places should treat you right, i'd say highbrook would be the friendlier place to go.

[Legacy GT-B]

Well, I'm an idiot. Secondary still boosted as it should yesterday, the only time I've tried to go above 3.5 grand in the last week, so it can't be blown completely yet. I figured if it's blown I couldn't fuck it up any worse than it was, so I might as well try and see where I was at. Will do a clean of the vacuum system as soon as I get a can of upper engine cleaner, hopefully that will narrow the problem down. Just wondering, if any of the lines of the BBoD are leaking, where would I find spares for them? Seeing as Subaru aren't the only ones with sequential twin turbos, would any old car speciality shop stock them?

On a more positive note, she used to idle really badly since I started using her as my daily until two weeks ago, especially when on the turbo timer, but since I've been taking her to tech in town and back she's been idling really well. Guess that's one less problem to solve, at least :grin:

[Reuben]

You may just have been an idiot indeed. Let's hope that's the case, as it's cheaper to fix than a blown secondary!

Put simply, secondary is only fully kicked up above 4000rpm, and you need to be flat tack to use it.

Have a read of this, you drive a TT now, you need to know how it works!

viewtopic.php?f=59&t=10991 (https://sl-i.net/FORUM/viewtopic.php?f=59&t=10991)