Turbo control in a GM ECM

[Shannen Durphey]

Ludis Langens wrote:

> Shannen Durphey <shannen at mcn.net> wrote:
>
> > >
> > > >The turbocharged diesels with efi (94-current 6.5) use a pwm control to
> > > >a solenoid in the vacuum line to the wastegate.
> > >
> > > Vacuum?  Vacuum?  During turbo boost?  :-)
> >
> > Yup.  Diesels have no natural vacuum.  GM uses a pump on the front to
> > supply it to the wastegate sol.
>
> The 2.8 MPFI V6 is a gasoline engine.  What I was getting at is: when the
> turbo is running, and the throttle is quite open, there shouldn't be any
> vacuum anywhere in the intake or exhaust system.  Of course, for a wastegate,
> all that matters is relative vacuum.
>

Actually, the vacuum from the vacuum pump is routed through the control solenoid
directly to the wastegate.  It is never connected to the manifold.  And yes, of
course there shouldn't be vacuum if there is boost pressure... unless possibly at
a venturi within the intake passage?  This last is just speculation, and I have no
idea if there is any practical application that does this.

> > > >Boost is measured by a map sensor.
> > >
> > > Yup.  And it also "runs" the engine.
> > >
> > Not on this app.  TPS is in gas pedal (Accelerator Pedal Position), no
> > throttle cable, stepper motor operates injection pump, fuel is delivered
> > based on APP and RPM.
>
> As I said, this engine is gasoline engine and it is a MAP (as opposed to a
> MAF) system.  I can say with 100% confidence that the absolute position of
> the accelerator (via the TPS) is never used to control fuel delivery.  (Unless
> the MAP sensor is broken and a substitute MAP is being computed from the TPS.)
> Short term relative changes in the TPS do affect the fuel delivery - but I'm
> still chasing after those.
>

Interesting.  Those GM classes left me with the impression that TPS is one of the
major players in fuel calculations.  But I have never gotten any specifics about
the programming.  However, I could probably bet you succesfully that there is one
time when TPS has a very direct result on fuel delivery.  During cranking, more
than 80% throttle will cause the ECM to lean out mixture, as much as 50:1 on some
applications.  But I suppose that's an unfair bet.  I see your point, though.  At
a fixed throttle position, fuel delivery is based on MAP, Coolant temp, rpm, and
O2 signal.  TPS is probably checked only for changes, and these greater than a
certain amount.  TPS changes would only cause a temporary enrichment or leaning
out for acceleration or deceleration, respectively.

So more about the turbo maps, please.  Would you say that a person could install a
turbo on a 2.8l Fiero, and assuming he could determine appropriate wastegate
control, have a running machine with no prom changes?

Didn't someone say that all GM proms have turbo calibration maps included?  If so,
does that mean I could rob a turbo from a 2.0l Pontiac and install it on my 2.2l
Chev. without sacrificing my computer?




>                    unsigned long BinToBCD(unsigned long i) {unsigned long t;
> Ludis Langens         return i ? (t = BinToBCD(i >> 1), (t << 1) + (i & 1) +
> ludis at netcom.com                 (t + 858993459 >> 2 & 572662306) * 3) : 0;}