On May 8, 5:21=A0am, "Mortimer" <m...@[EMAIL PROTECTED]
> wrote:
> "Mike" <m...@[EMAIL PROTECTED]
> wrote in message
>
> news:idtUj.2680$Cn4.1797@[EMAIL PROTECTED]
>
>
>
> >> How much fuel does an engine use when you are going downhill with
your
> >> foot off the throttle, using engine braking? I'd expect it to be
about =
as
> >> much as with the engine idling.
>
> > Most don't use any fuel as the computer shuts the injectors off on
decel=
..
> > You can see this on a scan tool by monitoring injector pulse width
which=
> > will go to zero.
>
> >> Is the fuel consumption the same if you coast downhill with the
engine =
on
> >> but the clutch pressed and/or the transmission in neutral?
>
> > =A0It would be higher in that case as the injectors would be supplying
f=
uel
> > to the engine.
>
> Ah, so if you go downhill with your foot off the throttle and the car in
> gear, fuel consumption will be zero because the computer will reduce the
> injector pulses to zero, but if you do the same with the car in neutral,
> there will still be fuel being injected at the idling rate? I hadn't
> realised that the computer could distinguish between these two cases.
>
> So in a modern car, my grandpa's old fuel-saving technique (a left-over
fr=
om
> driving during WWII!) of slipping the car into neutral as he was slowing
> down on the approach to a junction would actually be counter-productive!
Totally wrong.
The engine at highway speed will be turning 2-3000 rpm. That
compression ALONE will retard your speed and cost you FAR more in fuel
economy because you will be forced to come back on the gas earlier to
maintain speed.
I am not talking about slowing to a stop...I am talking about
integrating coasting into your driving as a hybrid already does.
Listen, I've driven a Prius over many miles, city and highway. There
were some times I went 3 miles on no fuel by being as aggressive as
possible with the battery and having good downhills and not
jackrabbiting at lights.
On certain downhill sections of highway, certain ramps, the Prius goes
into neutral and shuts its engine off. I used to do the same neutral
thing w/ my Passat and saw actual acceleration by gravity at highway
speeds, whereas I had to use SIGNIFICANTLY more fuel to overcome
engine pumping losses while in a drive gear. Almost every car has an
instantaneous consumption meter...at least VWs do.
If you coast down a hill and roll out in neutral, you are using idle
fuel. If the car is in gear, you will not gain as much speed on the
downhill and your engine will brake you on the flats, requiring MUCH
earlier throttle.
Jeezus, this stuff isn't revolutionary.
Trav
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