Date:         Mon, 17 Mar 2003 13:35:04 -0500
Reply-To:     Jay L Snyder <Jay.L.Snyder@USA.DUPONT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jay L Snyder <Jay.L.Snyder@USA.DUPONT.COM>
Subject:      How Does Timing Affect Idle Mixture?
Content-Type: text/plain; charset=us-ascii

I was doing some AFM tuning this weekend on my 1.9 Digijet with the Bob
Donald's Euro ECU.  I love the power, but miss the mpg.  I installed one of
Ken Lewis's O2 Sensor Displays under my dash.  This is an excellent tuning
aid and a very neat tool to have.  (See http://neksiwel.20m.com/)  By
adjusting the AFM spring, I was able to get the mixture a little leaner and
my gas mileage has returned while retaining the power of the new ECU.  I
got 21.3 mpg on Sunday.  Previously the best  I could do with this ECU was
around 18 to 19 mpg on the highway.   (The stock ECU, for comparison, would
sometimes get me 22s on long trips.)
Back to my main question.  I have my timing advanced to 5 BTDC, which is
about 10 degrees advanced from stock.  I have been running this way for
quite a while and this was even suggested by Bob Donalds.  With the O2
sensor disconnected, I am having trouble getting the idle mixture adjusted.
It is running  lean even with the idle mixture screw all the way in.
(When the O2 sensor is re-connected, the mixture is corrected.) The problem
is on cold starts, the O2 sensor doesn't do anything for about a minute or
so until it heats up, so cold starts are a little funky.  If I retard the
timing back towards the stock setting of 5ATDC, will this have a richening
effect o the idle mixture?  It seems that tightening up the AFM spring has
added to this idle mixture problem.  I didn't see the lean idle mixture
before this weekend.   Is the AFM flap supposed to be moving around at
idle?  I am thinking it is now held shut by the higher spring tension.  My
AFM is 18 notches tighter than when purchased new.   The display still goes
to full rich (1.0VDC) when the pedal is touched and goes full lean when the
pedal is backed off.  It is still getting plenty of gas, and  I think there
may be a few more mpg left in it yet.  I need to get the idle sorted out
first.  First, I will back the timing off to TDC (split the difference) and
see if that helps the mixture.  If not, back off the AFM spring a few
notches.   Any other ideas?
My guess is:  Retarding the timing will force me to open up the idle screw,
which will in turn allow the mixture screw to have more of an effect.

                                                                        Jay
Snyder



This communication is for use by the intended recipient and contains
information that may be privileged, confidential or copyrighted under
applicable law.  If you are not the intended recipient, you are hereby
formally notified that any use, copying or distribution of this e-mail,
in whole or in part, is strictly prohibited.  Please notify the sender
by return e-mail and delete this e-mail from your system.  Unless
explicitly and conspicuously designated as "E-Contract Intended",
this e-mail does not constitute a contract offer, a contract amendment,
or an acceptance of a contract offer.  This e-mail does not constitute
a consent to the use of sender's contact information for direct marketing
purposes or for transfers of data to third parties.

 Francais Deutsch Italiano  Espanol  Portugues  Japanese  Chinese  Korean

            http://www.DuPont.com/corp/email_disclaimer.html