Date: Wed, 10 Aug 2011 18:39:53 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Help! Hesitation on the road!
In-Reply-To: <CA+So782cdt=X4dkXx0du5s6j-6qC_00GZYmaQrKDRtuQUeTg-g@mail.gmail.com>
Content-Type: text/plain; charset="us-ascii"
That harness has limited success in solving the problem and part of that
solution is the effect of modifying the AFM output. VW was wrong.
The O2 sensor circuit is the only circuit that actually calibrates to a
signal, a real voltage, not a resistance change. When the signal is weak or
there is a noise or ground problem the ECU will continue to richen the
mixture until it sees that signal. A bad ground reference or a shorted input
lead will even override the effect of disconnecting the sensor. The ground
reference is the brown wire that travels in the distributor harness. Often
it is connected to a screw at the base of the oil breather. The plastic does
not make a good connection. Move it and if the wire in the crimp is brown
replace a crimp ring terminal. For wire testing do the following:
Disconnect the O2 sensor and peel back the outer wire sheath to expose the
outer shielding. Yes this is a coaxial wire.
Key on-Engine off, with a sensitive or digital voltmeter measure between the
outer shield and a good reference point on the chassis. Should be real close
to 0 volts.
Measure from center (signal) wire to same reference. Should be .5 to .6
volts.
Measure from center to shield. Should be same as center to ground.
Any stray voltage on that shield gets added to the voltage setting the O2
sensor circuit is looking for. So let's say you see .25 volt on the shield.
The ECU will not reverse and lean out the mixture until the O2 sensor puts
out ~1.0 volt. Since normal regulation is somewhere between .2 and .8 you
can see where this can mess things up.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
george jannini
Sent: Wednesday, August 10, 2011 4:16 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Help! Hesitation on the road!
I Googled...
VW technical service bulletins regarding driveability complaints read as
follows- The first details problems with Digifant engines and the second one
supercedes the first, acknowledging problems with Digijet Waterboxers as
well.
--- Begin quote ---
Technical Bulletin Group: 24 Number: 92-01 Date: February 29, 1992
Subject: Vanagon Intermittent Misfire Model(s): All Vanagon Digifant Fuel
Injection Engines
CONDITION After driving for 1/2 to 2 hours at a constant speed, vehicle
experiences lack of power, cuts-out or stalls, often accompanied by bucking
or jerking of the vehicle. In ALL cases, the vehicle will restart
immediately.
This symptom may not re-occur for several weeks/months. Inspection by the
dealer results in nothing conclusive. Some air-flow meters may experience a
vibration resonance of the metering potentiometer wiper during extended
constant driving. This resonance causes the air-flow meter to supply an
intermittent signal to the Digifant ECU. The ECU will then default to a
"no-load" condition and reduce the injection time.
SERVICE Harness, Part No. 025 906 302, is available to resolve this
condition. * remove electrical connector from air flow sensor (see Figure
24-174) * install converter assembly, Part No. 025 906 302, between harness
and air flow sensor NOTE If customer complaints persist after performing the
above repair, contact your Zone Product Support Specialist (TSM in Canada)
____________________________________________________
Technical Bulletin Group: 24 Number: 92-02 Date: April 30, 1992
Subject: Vanagon Drivability Complaints Model(s): All Water Cooled Engine
Vanagons SUPERCEDES TECHNICAL BULLETIN 24-92-01 (February 29,
1992)
CONDITION After driving for an extended period of time at a constant speed,
the vehicle may, on occasion, experience a deterioration of performance
which may be accompanied by a hesitation or surging. In many cases, after
turning off the engine and subsequent re-start or without having taken any
action, the symptoms disappear. These symptoms may not recur for several
weeks or months.
SERVICE To resolve this condition, wire harness Part No. 025 906 302,
should be installed. This harness provides improved signal voltage
stabilization. * remove electrical connector from air flow sensor * install
wire harness, Part No. 025 906 302, between main harness connection and air
flow sensor connection.
--- End quote ---
