No subject

resistor to the ECU ... I think I may have gotten one of Paul's first
attempts, and frankly I never installed it because of my concerns ... so I
can't even say for a fact it was an R-Z mod (but I will dig it out an look
this weekend) but I do seem to recall it was more than a single resistor.

The thing is that simply adding a resistor would not normally cause any
change assuming a high impedance circuit ... so I guess that means the
circuit the pressure transducer is hooked up to may not have a high input
impedance ...

The reason people use a resistor with the zener is that a zener diode will
sink as much current as it can to try to keep the voltage across it
relatively constant once it reaches its zener "knee" ... the resistor is
usually there to protect the voltage source ... in this case the pressure
transducer.

All that said ... even if the single resistor does modify the sensor output,
the fact of the matter is that the ECU is operating under a mistaken
impression that the engine is operating at a different point than it is in
fact operating at ... which may not be a problem, but seems
counter-intuitive to me.  I'll continue to prefer a method where the ECU
response is based upon a knowledge of the true operating state of the engine
...

I see some folks talking about computer controlled valves to fool the
pressure transducer ... if you think about it this is a mechanical analogue
to the zener diode.  This method does not need to be that sophisticated so
as to require computer control ... I've heard people have some sort of
pop-off valve that simply releases pressure above a certain point.  I'm
wondering if you didn't attach the controlled port of a standard adjustable
pressure regulator to the manifold pressure port on the ECU if you couldn't
do the same thing ...

Steve Buchholz
San Jose, CA (USA)

> > >and will advance timeing across the board.  I have modified mine so I
can
> > >set the value a bit higher as the timing with 475 ohm tends to be a
> little
> > >to much advance, especially on a hot day under load.  A fixed value
> closer
> > >to 600 ohm may be a better bet.
> > >
> ... Paul's mod to the ECU was a resistor/zener mod, not simply a resistor.
> The zener clamps the input to the A/D so that the ECU never thinks it sees
a
> pressure above that point and thus does not activate the overboost
shutdown
> mechanism.  Many people swear by this mod, claiming many miles of trouble
> free service, but personally I would not recommend doing it.  As long as
all
> is well it may be fine, but be sure to keep all of the car in tip top
shape
> at all times, because if you get something like a tear in the WG diaphragm
> things may change in a hurry.