Too much of a good thing(boost)

RYAN ALAN HOITINK rahoitink at
Mon Mar 31 20:57:11 EST 2003

Hello all, I have been trying to figure out a
problem I have had for a couple of months now.  One
day a boost problem showed up on my '87 5ktq.  First
off, let me say that I have a QLCC chip, 1.6 bar
spring, adjustable wastegate spring seat, and bypass
valve installed between the IC->Intake hose and
turbo cold side intake hose.  This combination
worked very well until shortly(not immediately)
after I modified the wastegate to be adjustable.
The condition is such that if I apply more than
about 1/2 throttle in most gears, the boost will
quickly rise and go right up to the 1.95 bar fuel
pump cutout.  Especially in 2nd and 3rd gears.  In
trying to diagnose the problem, I disconnected the
WGFV->Wastegate vacuum hose, not plugging the
wastegate or hose.  This had the effect of limiting
the boost to 1.6-1.7 bar, so I assumed that the
spring was doing its job and opening up the
wastegate at the prescribed boost level.  This led
me to conclude that the WGFV, its electronics, or
one of the lines leading to it was the problem.  So
I thought, why not just eliminate it and go with the
Schrappnel Knobben(tm)?  Which is what I did
tonight, using the Sears valve that's recommended on
Ben Swann's "boostin" webpage write-up by Paul
Timmerman himself.  I connected the input for the
valve to one of the nozzles on the top/rear of the
intake manifold, and the output to the top nozzle on
the wastegate.  The arrow on the valve points toward
the wastegate.  I blocked off the vacuum line that
led from somewhere in front on the passenger's side
to the WGFV, and connected the line that led from
the intake to the wastegate to the other line that
led from the intake(right next to it).  I assumed
that this was effectively creating a closed loop,
and provided more or less the same result as
plugging it.

Here's the problem... I get the same result as when
I had the WGFV attached... even when I turn the
pressure regulator all the way down! (in the "-"
direction)  I thought that with the regulator all
the way down(5psi min), the top of the wastegate
would actually see less pressure than if it were
vented to atmosphere, and that the wastegate would
open sooner.  This problem is really annoying, and
forces me to drive with a light foot.

I know that the WG diaphragm is in good condition,
as it holds pressure/vacuum.  The only thing that I
can think of is that there may be a problem with the
line going to the lower half of the wastegate.   The
line is physically in good condition, but could it
be plugged?  Would that cause this result?  The
thing that really baffles me is that the wastegate
seems to work fine when I vent the top half to
atmosphere, so I don't think it could be that the
wastegate is stuck.

I've been to SJM's website, and gone through the
tests, and everything seems to check out fine.
Especially now that I have the WGFV eliminated and
manually adjustable pressure regulator installed,
what could be the problem?

Any help would be appreciated.



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