Boost is not consistent

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Ctown8
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Boost is not consistent

Post by Ctown8 »

I always feel bad creating new topics but I've been doing a ton of reading on here and over on NASIOC and I still have not found an answer/solution to my problem.

Basically my 92 Legacy Turbo is not hitting full boost all the time, lately (being since Wednesday, today is Friday) when I'm on the highway usually in fourth or fifth gear, the car will only hit up to 5 -7 psi and it feels like its chugging. The higher the RPM the less this problem occurs, 1st, 2nd, and 3rd gear don't seem to have the same issue and before this started happening, usually 4th and 5th were where I would get the best boost ie. quick spool right to 10 -12psi. But now it seems like its struggling in those gears.

The car has a 3.5" turbo back exhaust (which sounds beautiful), diamond coil pack, Group N engine mounts(i think), and according to the guy I bought it from a Revtronix stage 2 tune (he said Revtronix 2, i assume he meant stage 2).

I've owned the car for roughly a month now and its been absolutely full of power until this last week, it definitely has a loss in power but not all the time, when it boosts normally the car feels good and powerful, but when its not boosting well, obviously it feels limited.

I've cleaned the maf twice and reset the ecu both times, this seemed to help but after a certain amount of driving it would seem to act up again and come and go.

I was hoping it was just a bad tank of gas but I filled up again yesterday and its still off and on. Its really frustrating, and I can't seem to find a permanent solution.

My guesses (judged by stuff I've ready) are going to be either the boost solenoid, the waste-gate actuator, the coolant temp sensor (I'm not sure why this one, just what I've read), other than that I'm not too sure.

Looking for suggestions here and hopefully answers.

Also, no CEL's but i have not checked for stored codes... I'm still new to this whole obd1 thing. I do have a usb obd cable though.
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
Ctown8
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Re: Boost is not consistent

Post by Ctown8 »

I'm a bit disappointed I have no reply yet :P but I've been doing more reading and had a new experience yesterday.
Lately my eyes have been practically glued to my boost gauge while on the highway trying to pin point this boost issue, and I noticed that after I had been driving about 110km/h for a few minutes in fifth, the boost seemed to react faster to my feathering the throttle on and off. So i thought of the issue is gone again... so i gave it more gas, enough to hit full boost, it started to climb good and fast up to about 7-8 then it quickly dropped back to 5-6 and started to bog a bit like it does sometimes. Very frustrating, seems like driving differently affects how the boost reacts.

Also a side note, I did the coffee cup mod today, sounds a bit louder, it didn't seem as great as its hyped up to be :P but definitely more whistle, I was hoping for wuuutututu (as Marty and Moog say), guess I'll get that when I do the intercooler.

I'm going to borrow a buddies MBC to see if its the BCS, if i can at least rule out that its not just a defective BCS that would be nice. I redid a bunch of vacuum lines today as well so I'm hoping that makes a difference. I checked for leaks with starter fluid but I found none so I'm hopeful. I'm not too sure what else I can test easily, also I saw some oil residue in the intake (in the ribbed 90) not sure if this is normal or if I may have a bad seal.

Also on the note of the coffee cup mod, do I really need to connect the bottom line? The one that comes of the bottom of the BCS, it was semi cracked off the old intake anyway. I just have it hanging right now, but it wouldn't be hard to hook it up if you guys think I should.

Another note about the coffee cup mod, the low end rpms do seem a bit more... perky haha.

Uhh, I think I'm going to go do my front struts now :(
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
wtdash
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Re: Boost is not consistent

Post by wtdash »

Ctown8 wrote:
Also on the note of the coffee cup mod, do I really need to connect the bottom line? The one that comes of the bottom of the BCS, it was semi cracked off the old intake anyway. I just have it hanging right now, but it wouldn't be hard to hook it up if you guys think I should.
Hi,
This line is part of your vacuum system - incl. the boost control - so it needs to be hooked up, or plugged if using an MBC (plugged on the BCS AND ON THE INTAKE). If yours is just 'hanging' then your BCS isn't plumbed correctly for boost control.

This 'could' be the source of your issue.

Image

GL,
Td
Last edited by wtdash on Sun Feb 15, 2015 7:57 pm, edited 1 time in total.
Turbo Subies:
'87 GL-10 Turbo - SOLD
'90 BJ EJ22T/DOHC & 5speed swap - SOLD
'04 FXT, Forged internals, VF39, STI TMIC, Cobb AP- SOLD
'93 Legacy SS - 5-speed, SOLD :-(
'02 WRX -SOLD
'96 BD-turbo'd-SOLD
'98 SF - NA-T
Legacy777
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Re: Boost is not consistent

Post by Legacy777 »

I agree with Todd, if the vent line for the BCS isn't hooked up to a vacuum source on the intake manifold that very well could be your problem. I'd suggest fixing that. You can try a MBC instead if you want.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
Ctown8
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Re: Boost is not consistent

Post by Ctown8 »

wtdash wrote:
Ctown8 wrote:
Also on the note of the coffee cup mod, do I really need to connect the bottom line? The one that comes of the bottom of the BCS, it was semi cracked off the old intake anyway. I just have it hanging right now, but it wouldn't be hard to hook it up if you guys think I should.
Hi,
This line is part of your vacuum system - incl. the boost control - so it needs to be hooked up, or plugged if using an MBC (plugged on the BCS AND ON THE INTAKE). If yours is just 'hanging' then your BCS isn't plumbed correctly for boost control.

This 'could' be the source of your issue.

Image

GL,
Td
I was just thinking about this, because it probably requires a certain level of vacuum to open or help open the solenoid. gonna go hook this up now! thanks guys. I will give feedback when I'm done!
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
Ctown8
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Re: Boost is not consistent

Post by Ctown8 »

Well I hooked all the vacuum lines up correct now, have not tested it yet, but will later today, also got one more strut in haha that's 3/4 now in a little over a month since I did the first one :P.
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
Ctown8
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Re: Boost is not consistent

Post by Ctown8 »

Drove into the city today, car felt good in town before I hit the highway, the second I "pulled" on/onto the highway I could feel that the car was doing its low boost thing, anyway, I went into the city, drove around for a while, had food, then I started driving home, while in the city the car was still driving funky, but when I got back on the highway it was back to normal, ie. good responsive boost <3 and it was good the whole drive home on the highway. So I got my fingers crossed that the ecu was just learning in the meantime and is now good, but I'm somehow doubtful.

Will update later.
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
wtdash
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Re: Boost is not consistent

Post by wtdash »

Ctown8 wrote:.... the ecu was just learning in the meantime and is now good,
The ECU does take a few 'pulls' / sessions to relearn if something was out of whack or was reset. Hopefully you're back to optimum operation.
GL,
Td
Turbo Subies:
'87 GL-10 Turbo - SOLD
'90 BJ EJ22T/DOHC & 5speed swap - SOLD
'04 FXT, Forged internals, VF39, STI TMIC, Cobb AP- SOLD
'93 Legacy SS - 5-speed, SOLD :-(
'02 WRX -SOLD
'96 BD-turbo'd-SOLD
'98 SF - NA-T
Legacy777
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Re: Boost is not consistent

Post by Legacy777 »

Did you reset the ECU after you fixed the vacuum hoses?
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
Ctown8
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Re: Boost is not consistent

Post by Ctown8 »

I did not reset it, I was in a rush and thought it would just re learn anyway, but I guess I will reset it tonight. Can I just unplug the battery to reset it, or is there a benefit to using the connectors under the dash? Also, if I reset it and its immediately back to normal then that should mean it was the vacuum leak causing the boost issue. If its the same ie. not normal, right after I reset it, then can I conclude its a mechanical failure as opposed to electronic failure?
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
Legacy777
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Re: Boost is not consistent

Post by Legacy777 »

Yes, disconnect the battery to clear all the learned fuel trims. Using the connectors just clears the codes and doesn't reset the ECU.

If after resetting it everything is normal then yes the vacuum line being off was the problem (mechanical).
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm
Ctown8
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Re: Boost is not consistent

Post by Ctown8 »

Thanks, I will reset, monitor, and update later.
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
Ctown8
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Re: Boost is not consistent

Post by Ctown8 »

So I reset the ecu yesterday and drove into the city for a movie, car was driving much better than usual so I was pleased. 1st through third felt normal, but fouth was still sluggish, and fifth basically still had the problem, but if I got the car up to a certain rpm then the boost levels would rise slowly up to normal (normal being 10 - 12). Its kinda odd, and I'm pretty sure its the boost pressure solenoid. I will borrow a friends mbc sooner or later to see if the boost acts normally with the mbc.
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
Ctown8
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Joined: Sat Dec 20, 2014 5:35 pm

Re: Boost is not consistent

Post by Ctown8 »

I purchased an mbc online a couple days ago, so ill wait to get that in the mail, in the meantime I'm going to replace the vacuum lines between the turbo and the bcs. While doing that I'll try putting some seafoam into the solenoid to see if that loosens something up.
1992 Subaru Legacy Turbo 5MT
2000 Toyota Celica GT
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