--- jon@dakota-truck.net wrote:
>
> "Bernd D. Ratsch" <bernd@dodgetrucks.org> wrote:
> >> From: Phil Jenkins [mailto:bugnik@yahoo.com]
> >
> >> Ok, I hook up my scanner with engine off. I have
> 29"
> >> of barometric pressure from MAP sensor. Start
> truck,
> >> at idle I have about 11" showing on the scanner.
> >> 29-11=18" of vacuum. I plug the exhaust and have
> 20"
> >> on the scanner. 29-20=9" of vacuum. Less vacuum
> with
> >> exhaust plugged, higher reading on scanner. Does
> that
> >> sound right? (Pouring some gasoline on the fire.)
> >>
> >> Phil
> >
> > You have 11" manifold vacuum at idle or 11" MAP
> vacuum? 29" BARO is normal
> > though. What is the 20" you're talking about?
>
>
> Neither - the 11" he is referring to is a
> pressure reading (from
> the MAP sensor), not vacuum. The 20" is the
> (pressure) reading after
> he plugged the exhaust. All of the readings he gave
> are direct
> pressure readings from the MAP sensor. Determining
> vacuum from the
> MAP readings can only be done via calculation, which
> is why he
> subtracts them from the barometric pressure to
> obtain the vacuum
> values.
>
>
> --
> -Jon-
>
Thanks Jon, that is exactly what I'm saying.
Phil
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