Your basic fuel/air adjustment is out of whack.  With the O2 sensor engaged
the ECU can make some compensation.
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Tom Young                       '81 Vanagon
Lafayette, CA 94549         '82 Westfalia
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----- Original Message -----
From: "insyncro" <insyncro@HOTMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, February 07, 2004 8:45 AM
Subject: Re: ECU question, w/ O2 disconnected

> I disconnected the O2 and right off the bat it ran rough at idle and blew
> black smoke while at highway speed with the same amount of hesitation.
> Where to next?  AFM?
>
> dylan
> ----- Original Message -----
> From: "Dennis Haynes" <dhaynes@OPTONLINE.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Saturday, February 07, 2004 11:19 AM
> Subject: Re: ECU question
>
>
> > This type problem is almost always related to the O2 sensor circuit.
> > Does your sensor have the heat shield/deflector in place? Is the wiring
> > good? Is the O2 sensor heater working? The ECU tries to go closed loop
> > at ~120 and 1 minute running. If the O@ sensor output is not sufficient,
> > the ECU will keep richening the mixture to get the signal. If not
> > working, yet, it will go rich enough to choke the engine. Disconnect the
> > sensor for a test. If the problem stays away, then the problem is there.
> > When the sensor is disconnected, the leakage of the input circuit of
> > about .5 volt fools the ECU into thinking the mixture is ok so it does
> > not make any adjustment.
> >
> > Dennis
> >
> >
> > -----Original Message-----
> > From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
> > Of Dylan Friedman
> > Sent: Saturday, February 07, 2004 10:07 AM
> > To: vanagon@GERRY.VANAGON.COM
> > Subject: ECU question
> >
> > Hello List,
> > The patient is an 87 Syncro van, that has some hesitation after warm up.
> > I
> > have checked the grounds, ICV & ICU, temp sender and the AFM.  Still no
> > change.  If I turn off and reset the computer all seems to be fine for a
> > short period of time, but starts slight hesitation soon after.
> >
> > My question is concerning the ECU computer.  How often do they good bad?
> > What is the best way to check it?
> >
> > Can I rule out fuel delievery problems because it runs fine after a
> > reboot?
> >
> > Thanks
> >
> > dylan
> >