manual boost controllers, and ECU functions

[Robert Deis]

On Mon, 29 Jan 2001, Ken Keith wrote:

> I was wondering what it is that the ECU on, for example, and MC-1 
> motor really does.  I think it basically controls timing, by retarding 
> it if it detects knock, and also controls the frequency valve (?, or 
> something) to keep the mixture as close to stoich as possible.

Yes, from what I've read thus far.  It also controls boost via a solenoid
valve (not sure the name of the valve).
 
Under normal ops, the wastegate opens under a certain pressure set by the
spring.  There's some vacuum tubing that comes into play here, but it's
constant.

When warranted, the ECU opens a solenoid valve that allows manifold
pressure to help hold the wastegate closed- thereby assisting the spring
and raising the boost.

When the specified level is reached, the valve is closed, the assist goes
away, and the wastegate opens.

The ECU can modulate the valve to hold any boost level it wants.

> I guess my question is, what does a chip do besides raising the 
> overboost fuel cutoff?

It can raise the boost.  Other details I'll leave to Audi experts..

> Another question, would an SJM chip affect how quickly target 
> boost is reached?

I doubt it, becasue a stock ECU should do this:

>  I mean, does it hold the wategate completely 
> closed until the target boost is achieved, and only then begin to let 
> it open to keep the turbo from overspinning?

as well.  It just has a lower set point.
 
> If not, it seems like this boost controller setup would be beneficial, 
> even for chipped cars.

You could bypass the ECU controller and raise your boost without the chip-
but I dunno that thats a good idea...

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  Rob Deis                  "Let the people know beforehand what the law
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