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Steven Soknacki
Tinkerer
Ontario
'92 SC400 and '94 GT-T Limited

Posts: 97
Reg: 07-2006

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Friday, April 29, 2011 - 05:24 am, by:  Steven Soknacki (Sc_coupe) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Another week, another problem...

I've been commuting to and from school finishing up finals over the past few days, and haven't really got on the power as much. I noticed that it started seeming laggy around town - especially in 1st and 2nd where it will not build positive boost nearly as early as it should. I have not lost boost - it will reach a steady 0.75 bar as always. However, when I apply the throttle, it stays on vacuum for too long, hesitates to build boost around 0.25bar, then shoots up to 0.75. As a result, it does feel like I have lost power. It used to feel like the turbos wanted to go right after taking off - not so anymore.

What I don't understand is if it was a vacuum related-issue, why will it still make and hold full boost? Wouldn't it be reduced if I was losing pressure somewhere? Nevertheless, I've checked all lines thoroughly to no avail. They were all checked by a reputable shop less than two weeks ago as well.

Also, no smoke on start, idling, or after being on it. No change in noise from the turbos, and no difference in peak pressure. From the threads I've read most who lose an exhaust wheel report seeing lower boost than normal. I read Veronica's thread and held a screwdriver to the turbos and had my brother rev the car a bit - and no ungodly vibrations from either turbo, both were about the same.

My previous issues were ISCV-related, and for a bit it would idle low and dump fuel causing it to have gone through some excessively rich running periods since I've owned it. So could a clogged stock cat cause problems like this? The exhaust did feel unusually hot the other day...

Will try and ECU reset but it's a long shot.

Mods that may affect things:

Stock cat, 3" Exhaust back from there.
Blitz SBC (Set at 0.75 bar)
Blitz Access ECU
ARC BOV (new vacuum line, checked clamps)

Car is a '94 and has done ~140000kms. Turbos have always made a bit of noise since I purchased it, but nothing that seemed excessive compared to other 1JZ cars I have been in.

So what is it?

Wastegate issue? Sticking/cracked? Or do you think an exhaust wheel may have chose to part ways with a shaft? I don't have time to start pulling things apart at the moment but may start to this weekend. It's going into a shop on Monday.

Any help is appreciated.

-Steve
Ross Pesina
TryHard
Vic
Soarer T, Soarer TT, Supra TT,

Posts: 375
Reg: 08-2006

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Friday, April 29, 2011 - 01:45 pm, by:  Ross Pesina (Ross79) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

It's definately not a lost turbine wheel as you would have noticed a massive loss in power everywhere. From from you have written it's just an increase in lag.

I'd be checking all your vac lines for a leak. It could be wastegate remaining slightly open which would increase lag until the volume of air at higher revs overcomes that.
It could be a leaky bov. I'd start with vac lines as it's the cheapest and easiest thing to check.

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