Date:         Fri, 29 Aug 2008 22:25:29 -0400
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
Comments:     RFC822 error: <W> MESSAGE-ID field duplicated. Last occurrence
              was retained.
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Re: When the O2 sensor cools down...
Comments: To: pickle vanagon <greenvanagon@GMAIL.COM>
In-Reply-To:  <91c8f9760808291743s440a08d0yd270ddf683372cc2@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Engine braking is strictly a function of the closed throttle causing high
manifold vacuum as the engine is being driven by the wheels. Yes, engine
braking is caused by vacuum, not compression.

The O2 sensor cooling is a design flaw. That is why the 2.1 engines use a
heated sensor. Also, the 1.9 liter vans originally had an insulated cover
on the outside of the sensor.

When the engine is over run with the throttle closed, the fuel is
completely cut off until the engine goes below 1,350 rpm. After this, the
O2 sensor is ignored for 25 revolutions. The is why the 1.9 engines often
get that idle surge.

Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
pickle vanagon
Sent: Friday, August 29, 2008 8:44 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: When the O2 sensor cools down...

Usually during engine braking it shows 0 volts for me.  Once the sensor
has
cooled, it needle starts to drift up towards center (.5 volts).  It then
stays around .5 volts no matter what your doing until the sensor warms up
again.

This brings up something else I was wondering: does engine braking work
when
the ECU is not in closed loop mode (for example at startup?)

-Wes

On Fri, Aug 29, 2008 at 7:34 PM, Jim Akiba <syncrolist@bostig.com> wrote:

> what does to voltage go to? does it drop way off?  During engine
> braking it should be quite lean which should show as low voltage on
> the narrowband o2
>
> Jim Akiba
>
> On Fri, Aug 29, 2008 at 6:59 PM, pickle vanagon <greenvanagon@gmail.com>
> wrote:
> > ...what happens?
> >
> > I rigged up a air/fuel mixture meter (just a voltmeter coming off the
O2
> > sensor) a few months back.  On our recent trip across the country, we
> > obviously spent some time driving in hillier country than we usually
do,
> and
> > I noticed something funny.  While engine braking down a long hill, all
> the
> > clear air coming through the exhaust system, while obviously hot, is
> > apparently not quite as hot as the sensor needs to be, so that it will
> > eventually cool down to the point where it no longer provides good
output
> > and behaves like it does right after startup.  After driving for a
> little,
> > it warms up again and output is normal.
> >
> > I'm wondering what the ECU does during this stage.  Does it know to
start
> > ignoring the oxygen sensor if it thinks its output doesn't make sense?
>  Or
> > does it just keep chugging along, thinking everything is peachy, and
> > consequently send too much or too little fuel as the oxygen sensor
fails
> to
> > react dramatically enough to the changes in ratios of the exhaust
gasses?
> >
> > -Wes
> > 1.9l westy
> >
>