MC Waste Gate Frequency Valve operational info

[Bernard Littau]

Hi List,

I am debugging a low boost problem, and I am down to the distinct
possibility that the waste gate frequency valve, or its input, are not quite
correct.

I get roughly the same max boost in all three of these cases: 1) no upper
hose on Waste Gate, 2) upper hose OK with stock ECU, and 3) upper hose OK
with 2.0 bar ECU.  When I remove the lower hose of the waste gate, or pipe
the manifold hose directly into the top of the waste gate bypassing the
solenoid, I get serious boost!  Everything else checks out, too.

Do any of you MC'ers out there know how the Waste Gate Frequency Valve is
supposed to operate in terms of inputs and outputs?

I can see the output is a duty cycle between pressure and vent duration that
allows the ECU to vary the pressure added to the top of the waste gate in
order to compel the waste gate to produce more boost by staying closed
beyond the waste gate spring pressure.

I haven't gotten out to the car to examine the input side -- I was hoping
some kind soul had already done this and could save me some steps.  I only
have a DMM, no scope, so I am a bit limited in my ability to track faster
signals.

My fantasy is that the input to the Waste Gate Frequency Valve is a variable
voltage from the ECU that is translated to a duty cycle frequency of on-off
signals to the Waste Gate Solenoid.  I would further fantasy that more volts
would mean give me more boost, please. (ECU's are very polite :-)

It would make sense in my case that the input is reduced in voltage, as the
duty cycle seems to be not aggressive enough to generate the ECU requested
boost.  Old wiring would certainly account for a voltage drop.  Hey, I can
hope I understand all this stuff ;-)

Does anyone have the SAE paper mentioned on Scott's web site describing the
operation of the MC boost control?  I am thinking the info I might wish for
is in that paper.
http://www.sjmautotechnik.com/10vwaste.html#mcsae

Thanks,

Bernard Littau
Woodinville, WA
'88 5ktq