Re: 505 Turbo wastegate actuator toughts

Joe Grubbs (jsgrubbs@ipass.net)
Wed, 05 Aug 1998 19:08:20 -0400

>
> Note that if I had the N9TEA circuit, I wouldn't be wasting my
> time trying to figure a way to do what the N9TEA would do if
> it had a maxxed out wastegate. I may in fact hunt down a N9TEA
> ecu, but there are other concerns. In particular, if the wastegate
> is adjusted say for 1 Bar. The electrovalve does it's thing and
> boost has to be dropped. Pressure however is at .85 and the
> wastegate doesn't open (the electrovalve only let the
> pressure reach the. Ok, then let's adjust it to .8 then? ok but now
> the wastegate triggers as it goes over .8 as the electrovalve
> opens, pressure drops to something unknown. This thing runs
> open loop as there is no pressure sensor to ride on the max
> boost and is not as efficient.
>

I might be misunderstanding what you are saying--It doesn't quite
work the way I think you have described--Here is breakdown of
how the whole adaptive boost control system works--

The wastegate allows exhaust gas to bypass the exhaust turbine,
ofcourse. The electrovalve on the N9TEA is placed inline with
the hose to the wastegate actuator.

There are three connections on the electrovalve--
Pressure from intake (after turbo)
Pressure to wastegate actuator
Bleed to atmosphere (which goes to intake hose just after airflow
meter)

When you crank the car up, and hit the gas pedal, the electrovalve
is pulsed by the ECU. The pulse openes and closes the bleed orifice.
As this point, the electrovalve is bleeding a lot of pressure, i.e.,
there is very little pressure acting upon the wastegate actuator.
When the ECU deems it necessary to reduce boost pressure, it reduces
the "on-time" of the electrovalve, causing more pressure to reach
the wastegate actuator. This increase in pressure causes the wastegate
to open, thereby reducing boost pressure.

Disconnecting the electrical connection to the electrovalve
causes the N9TEA to act like an N9T or N9TE--but boost pressure
will be pretty low, because NO pressure is being bled--all of it
is going to the wastegate actuator.

BTW, closed and light throttle conditions result in no signal
to the electrovalve--I guess to reduce wear on the solenoid.

Joe