Date:         Tue, 8 Sep 1998 16:55:53 -0500
Reply-To:     Darrell Boehler <midwesty@TAOS.MIDWEST.NET>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Darrell Boehler <midwesty@TAOS.MIDWEST.NET>
Subject:      afm tuning
Comments: To: vanagon list to post <vanagon@vanagon.com>
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Hi Volks,
        At bbta (busses by the arch) Bill Dummitt  found a  van running very
rich. The  main spring in the afm( air flow meter) was adjusted too weak
ccw. This caused a rich mixture in open loop( o2 sensor disconnected)  and
in closed loop the ecu would not / could not  correct for it.  Actually one
ecu out of 3  would correct the  mixture.
    I had adjusted afm  main springs on L-Jetronic but never had to on a
digifant.  I have seen some discussion on this today so would like to add my
experience and would like anyone to correct  any errors,  problems or bum
dope they see.
    I feel your engine and other tune up items should be / must be  in
proper conditions before performing the afm adjustment.

Adjustment. (start with a warm engine)
1 pop the top from the afm
2 unplug the o2 sensor (forces open loop) attach lcd volt meter to the o2
wire.
3 start the engine and allow the o2 sensor to warm up and start getting an
output, 1-2 minutes maybe longer for digijets and L-jetronic.  It will most
likely and should be above 0.5 volts (at this point one  can tweak or
stabilize the mixture by varying the afm wiper position)
4 with the rpm at about 3k rpm adjust the afm main spring tension until the
meter reads 0.7 volts cw is leaner  (lower voltage) The main spring tension
is adjusted by turning a black gear type wheel. Pull the  wire detent out of
the gear or loosen  it so the wheel can be turned. Mark/ scratch  the gear
so the original position can always be returned to if necessary.
5 now with the van at idle adjust the   afm bypass screw so the meter now
reads 0.7 volts at idle.

This should result in a properly tuned afm. Connect up the o2 and observe
that the meter is now bouncing above and below 0.5volts indicating the
digifant , L-Jetronic, or digijet is now controlling the mixture to
perfection.

Darrell Boehler
Makanda Illinois