Date:         Sat, 21 Sep 2002 21:48:31 -0700
Reply-To:     Mark Keller <kelphoto@HIGHSPEEDPLUS.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mark Keller <kelphoto@HIGHSPEEDPLUS.COM>
Subject:      Basic Fuel Mixture was Measuring oxygen sensor output...bad air
              flow meter? AFM question
Comments: To: Jbclem <jbclem@EARTHLINK.NET>
Content-Type: text/plain; charset=us-ascii; x-mac-type="54455854";
              x-mac-creator="4D4F5353"

Hi John,

Well, I read your post and thought I'd add a thought.  One is that the
complete formula for initial injector pulse goes by: the Temp II,  the
AFM,  the hall output, distributor rpm signal-- BUT the ECU assumes the
fuel pressure is right.

So where to start. We first lets make sure that your are talking about
an engine that has completely warmed up, and your getting this reading
at 3000 rpm or better on the road.  At idle, the AFM spring tension is
not the adjustment to lower or raiser mixture.  The idle air bypass is
the adjustment for idle level mixture, and should be set after the
spring tension is finished.


The TEMP II in my opinion is a high failure item, and at $15 get
replaced often, I get 8 months before I sense the thing is getting
sloppy on cold starts.  I prefer the VW brand as they seem to close loop
faster from a cold start-up than the after market ones.  No difference
in my experience as to durability or accuracy.  I also recommend adding
the ground strap from the AFM to the head covered by service bulletin.
BTW the service bulletins are full of suggestion for grounds and wiring
harnesses to be in perfect condition.

To recondition my electrical connections I use Tarn-x clean the
oxidation off of them.  Fill a small spray Paint Cap sized container
with the tarn-x, dip the connector into it, then rinse well.  I then
coat the connector with OX-Guard or other electrical grease designed to
prevent oxidation.

If you haven't check the fuel pressure, it's also a possible failure
point.  I've; briefly Clamped the the fuel pressure regulators return
hose, with a pair of needle nose pliers , while watching a gauges  and
let the pressure go to 60 -75 psi and let go.  The book pressure is
29-36 psi;  low with vacuum, high without vacuum applied.  These are
target values and I'd say  the 7 lb range is more important than whether
your high or low of the target But the pressure value should change with
and without vacuum, and this may be your problem.

On the other hand, if all else fails, you can move the wiper arm on the
afm back a little.  I've moved mine back on the account I run a 50 psi
basic fuel pressure for a little extra scat!  Just look at where the
wiper is when the van is idling. and then experiment from there.  Good
Idea to point a magic maker dot where it used to be for reference.

This is a start.  I've written detailed versions of this brief overview
the archives. Just look under my last name

Sincerely,

Mark Keller
91 Carat