Date:         Wed, 1 Sep 2004 22:11:46 -0700
Reply-To:     Craig Oda <craigoda@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Craig Oda <craigoda@GMAIL.COM>
Subject:      Re: O2 sensor problems
In-Reply-To:  <b3a1e7ad040831235254f3c65c@mail.gmail.com>
Content-Type: text/plain; charset=US-ASCII

Thanks to the people on the list, I belive that I have resolved the
problem.  I've taken the van out for a 20 mile test run across stop
lights, city streets and the 280 hwy, billed as one of the most scenic
highways in the US.

For the benefits of others I'll describe the problem and solution.

Symptoms:
Occasionally no power at stop lights for about 3 seconds or more.  Van
would kind of crawl along at about 1 mph until the power kicked in
after a few seconds.  In addition, van was running rich.  Unburnt gas
smell.   Van ran fine with the O2 sensor unplugged.

Diagnosis:
O2 sensor is telling ECU that the engine already has too much gas and
to cut down on the gas to the injectors.  (Thanks to Paul for this
diagnostic).

Complication::
Normally, I would turn the fuel/air mixture adjustment screw on the
AFM to lean out the mixture.  However, in my case I had previously
messed up the AFM settings because I had previously opened up the AFM
and adjusted the wheel that tightens and loosens the clock spring.  (I
had a different problem last month with sooting of my previous O2
sensor that I had misdiagnosed and resulted in my foolishly opening up
the AFM and adjusting the spring incorrectly.)

Solution:
I took the cover off the AFM and tightened the ratchet wheel about 3/4
of a revolution. This is a lot.  Most people would probably need to
adjust it about 3 notches.  I really messed up the settings earlier.
I used a digital voltmeter connected to the O2 sensor to get a reading
of about 0.45V.   Someone earlier told me to get the reading at a few
thousand RPM.  I screwed the fuel/air mixture screw all the way  back
in, then unscrewed it out a couple of turns.  At this setting, I
tightened the ratchet wheel inside the AFM until the voltage reading
matched up.  I then sealed up the AFM with silicone rubber.

The van appears to be running fine now with a smooth idle right at
800rpm good throttle response after the stoplights and no smell of
unburnt gas.

If the problem does not reappear, I'll be moving on to fixing some
minor electrical problems with interior lights and installing a
permanent aftermarket tach.

Thanks again to the people on this list.


-- Craig

On Tue, 31 Aug 2004 23:52:50 -0700, Craig Oda <craigoda@gmail.com> wrote:
> Ever since I got my transmission back in, the van is running great.
> I'm driving the old beast to work every day, taken it to Linda Mar
> beach and to the SF zoo.
>
> The engine idles fine and hasn't died yet.  Transmission fluid (AT) is
> stable, no apparent leaks.
>
> I've got a couple of issues with the van that I want to solve
> eventually and I'm hoping some list members can help me out.  Due to
> lack of knowledge on my part, I often make the van run worse when I
> try to fix a problem with my 1.9L waterboxer with Digijet FI.
>
> The van is running rich.  It doesn't affect drivability, but I can
> smell the unburnt gas from the exhaust.  The fuel air mixture screw on
> the Air Flow Meter is all the way out, counter clockwise.  In a
> previous attempts to adjust the fuel air mxture, I messed around with
> the spring inside of the AFM and I can't get it back to the original
> setting.  (I didn't mark it.  :-(.  To lean out the mixture, should I
> tighten the spring or loosen it?
>
> In addition to running rich, I have weird behavior when the O2 sensor
> is connected.  If I disconnect the sensor, the van runs fine.  So, I
> disconnect the sensor when I want to make sure I get to work or to the
> park.  I'm on O2 sensor number 3.  It's a brand new sensor with less
> than 5 miles on it.
>
> When I press the throttle after a full stop at a light, the van will
> sometimes not accelerate for about 5 seconds.  Seems like a heck of a
> long time when cars are backed up behind me.  If I keep the
> accelerator floored, the van will eventually start to move.  This
> problem only occurs when the O2 sensor is connected to the ECU.  When
> I disconnect the O2 sensor from the ECU, the problem disappears.  I've
> run the van over 1000 miles since I had the problem with the old O2
> sensor sooting up.  I think that I've cleared the soot from the
> exhaust system.
>
> I have a voltmeter hooked up to the O2 sensor with the display for the
> meter mounted on my dash.  When driving, the volts will sometimes drop
> down to zero, indicating either a super lean mixture or something
> funky going on with my O2 sensor.  When the engine loses power, the
> voltmeter is saying that the fuel/air is super lean.
>
> Under normal driving, the voltmeter says that the engine is running rich.
>
> There are some other minor problems with the van, but I'm trying to
> trace the source of this problem first.
>
> Thanks.
>
> -- Craig
>