Date: Thu, 1 Aug 2002 08:40:48 -0700
Reply-To: Mark Keller <kelphoto@HIGHSPEEDPLUS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <kelphoto@HIGHSPEEDPLUS.COM>
Subject: Re: automatic performance
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Adam,
Probably a mis- adjusted fuel injection system. My 91' behaved this way
too. In fact my wife wouldn't drive it because of the "lag" from when
you hit the throttle to when something actually happened.
Any way I solved it by doing the air flap AFM adjustment that deals with
spring tension. I wrote about last year, archives should have it
For the best result consider, double checking the timing, and vacuum
hose connections, some vans screw up the pressure regulator and
distributor hose connection and they come from different sources. Also
cleaning the wiper arm on the AFM , beneath the black cover. The cover
is off for this whole procedure.
Check again the following that the idle and WOT switch is functioning
unplug at the connector and with the engine off , just read the ohms as
you operate the throttle. Should be continuity at full closed and full
open. I think a .005 th feeler gauge at the idle stop screw is the
tolerance, i.e. it should stay continuity until the throttle is open
that far. The adjustment is the two allen screws below the throttle
body housing. ONe locks the adjusting mech in place, loose it, the
other makes the adjustment.
If you want to skip all of this cause you have tinkered with it in the
past proceed, otherwise consider doing it. Also if you email me, I'm on
digest, I work with you to getting your van nice and snappy off the
line.
In case the archives don't suit you at the moment here is the main idea
is:
Go open loop , i.e. disconnect the O2, connect a digital Voltmeter to
the O2 black lead on a long wire, I used microphone cable, so that you
can view the mixture in volts while driving. The test target is to have
.5 volts or so at 3000 Rpm plus while driving, steady cruise, level-ish
ground etc. yes is will move around some but it will stay relatively
stable enough for you to determining whether the system is general lean,
.4 volts or less or rich .6 volts or higher. The values for the O2 Seem
to be .3 and .7 volts. The best lean of .15 and best power of .86 are
targets taken form Probst Book on Bosch Fuel injection., keep your
level cruise target to .5 or .6 volts. The injection system has a curve
built into it for acceleration and deceleration and the vacuum to the
pressure regulator is what keeps it all happy.
Adjustment is by changing the spring tension on the AFM flap. No need
to remove the wire gizmo that locks the gear in place, just lift up the
wire, move the gear, I THINK it was CCW 10 teeth for mine, put reference
scratch on you starting position.
This takes a tweaking or spiral engineering, to close in on a good
setting. BTW, I was extremely pleased with how well the open loop fuel
injection system control the mixture, in fact the Van runs better, but
the O2 is needed to protect the Cat for getting an over rich mixture and
melting should something go wrong during normal operation. YOu might as
well locate a hill, and then go up at 4400 RPM and see if the fuel pump
/ pressure regulator keep you mixture at above .5 volt during the
climb. This test the system for a possible lean out, when you really
need a power mixture, A. cooling, B. Power. Anything below the .3
mixture is unacceptable. If the spring tension is giving good mixture
at all other driving condition with the EXCEPTION of a full power WOT
hill climb of at least a minute or so, then I would look at the fuel
deliver system, pump and or regulator. Keep in mind this is done
without the O2 sensor connected to anything but the Volt meter.
Anyway, Having done that, go back home and set your basic idle at 840
Rpm, idle motor disconnected at it's plug. Use the large flat head
screw on the throttle body, putting a dot on the screw and the body for
reference before beginning helps keep your orientation.
Idle air bypass adjustment- Next remove the 10 mm or plug on the top of
the AFM, mine had been done before so there was already a 7/64 ths dia..
hole there to screw a #8 sheet metal screw into. Do that, wiggle the
thing out. Get a 6 mm allen wrench, put some 3M body caulk around the
wrench, as an air gasket, I just leave my in instead of replacing the
plug. Ok all of that was so you could look at the voltmeter and adjust
the Idle air bypass screw. Again look for .5 volt, yes it will float
around, but it should hang between .3 and .7 volts
Of course once the IDLE Air by pass is set, the idle will be off some,
re adjust the idle screw, now the idle bypass screw, until they both are
at the target setting.
Go back out and drive the van and your throttle response should be
amazing!!!
Sincerely,
Mark Keller
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