Ben Swann benswann at comcast.net
Thu Jan 29 00:04:43 EST 2004


It is far too long to remember all the specifics of my 5ktqs BPV plumbing idiosyncracies.  But I do remember the audible "whoosh" sound as a side result of it not being plumbed right, even though the improper plumbing was not where the bypass was directed to, but more of where the control line was.  I also recall that the boost was limited to around 1.4 but if I really tried hard, could push it to about 1.7 bar .  I was not doing good things to my turbo then, now that I understand what was happening as essentially I was putting the turbo in a closed loop causing it to spin excessivly while blowing off excess boost generated through the wastegate.

This may not be the problem at all, only it seems to much dejavu in what you described in comparison to what I experienced then.


"Ben Swann" <benswann at comcast.net> wrote:
> Before reading some of the other replies, I was thinking Bypass valve problem.  Your comment about the noise tells me something is not right.  Also, I recall when I first implemented a bypass operation on my now departed '87 5ktqa(QLCC chipped), I had a mysterious low boost - 1.4 (could maybe top at around 1.6 maybe 1.7 when pushing it hard).  After insisting my install was correct, I ultimately found it was not.  The vacuum control port I was using was not correct.  Some throttle bodies have 2 ports and one produces correct vacuum and the other some partial vacuum.  Anyway I should not have been using any port on the throttle, but a true manifold vacuum source - that resolved the problem and could get the desired boost I needed(over 2 bar0, and I am thankful I did not overspin my turbo, as apparently, bypass was kicking in too soon.
> Don't know how this may help, but have an inkling something may be wrong with what you did when changing the BPV.  
> If not then you likely have some leak that is occuring under pressure, and limiting your boost

Hi Ben,

Well, actually since this car had a BPV already, I just 
unhooked it all at the valve end of things, and never had to 
mess with the other end of the vacuum hose.  After I rule 
out the signal hose to the BPV, I'll verify that connection.

However, that said I would think that the whoosh I hear when 
I shift either wouldn't be there, or wouldn't coincide with 

Why does the comment about the BPV sound make you (and others) think something isn't right?  Isn't it supposed to 
make a noise when I shift?  Granted it shouldn't be loud 
since I have an airbox, and it isn't loud, but the timing of 
the whoosh seems normal to me.

Specifically, my bypass valve has the small vacuum signal 
port facing forward, not up.  This was how it was when I go 
the car, and seems to make sense since the pressure from the 
turbo outlet is acting on the side of the diaphragm.

I bet (and hope) that it is the BPV signal hose.  I can't 
wait to find out! :D

If the question was missed, do I need to use a cloth braided 
hose to replace the BPV signal hose?



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