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turbo diagnostic steps for low psi?

mikus

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Joined
Jan 11, 2007
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2,763
Location
Aurora IL

Hello - first, please bear with me.. I've searched & read up and have some ideas, but I'm hoping to leverage those with someone who has 'been there' (I'm car-savvy but very early into the turbo learning-curve)

Is a 1991, 145K and totally stock except 2g manifold. On test, I'm making max ±6psi from the turbo.. and it takes a while to get there, it's a slow & steady from 3000 to about 5500rpm 6psi.

I will diagnose over the weekend, & am looking for help understanding what is most/least likely culprit. Seems like these are some candidates I should look at. whaddya think?
- leak in system (pressure test at turbo, at TDC)
- turbo going south (inspect shaft play, blade damage, cavernous cracks)
- BOV or WG issues (i'm very foggy on these 2, need help)
- cat is clogged (is this really that likely a cause?)
- other?

Thanks in advance for your input!
 

Hertz

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Jul 29, 2002
Messages
13,501
Location
Chicago, IL
WG issue: the wastegate could be stuck open, or the area around the WG opening is cracked (very likely). Do you have a manual boost controller? Even with some good cracks, I was able to get my old 14b up to 15psi, so I would suspect a boost (piping) leak first.
 

mikus

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Jan 11, 2007
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Aurora IL
no MBC... it's a safe bet to assume I have nothing that's non-stock or cool in any way. 'cept a JDM cupholder.

Suggesting then, a MBC would allow me to adjust for the addtl air lost from a WG crack? thanks Ryan
 

OldHairyBastard

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Apr 27, 2005
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Northern Chicagoland Area
Were you able to find out what was causing your boost issue yet?

Doug
Quote:
WG issue: the wastegate could be stuck open, or the area around the WG opening is cracked (very likely). Do you have a manual boost controller? Even with some good cracks, I was able to get my old 14b up to 15psi, so I would suspect a boost (piping) leak first.

 

Hertz

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Joined
Jul 29, 2002
Messages
13,501
Location
Chicago, IL
Mine? Nope. Haven't looked yet. I'm going to start with checking the timing. I'm suspicious of the tone the motor makes at > 3500rpm. EGTs don't suggest that the timing is off, however.

Then I need to go fill my air tank and do a pressure test.
 

steve

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Sep 11, 2003
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18,897
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NJ
Ooh fancy. Haven't used it yet though. /ubbthreads/images/graemlins/wink.gif

img.php
 

try to release the exhaust pipe from first flange before cat, go around and wake up the neighborhood (much better if done at midnight), if problem continues,you might need new bearings in your turbo. Good luck.
 

mikus

Well-known member
Joined
Jan 11, 2007
Messages
2,763
Location
Aurora IL
I found a great general link for the next person searching on this topic:
link
seems to cover the basic diagnosis well
 

You have an aftermarket boost gauge? The stock boost gauge is kind of funny how it reads vac/pressure.

I have the same problem with my 1G right now. My problem is the seals are blown on my turbo and the blow by is insane. The stock turbo wastegates tend to rust as well and get stuck open.

I would build a pressure checker and go from there.
 
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