[Diy_efi] O2 says rich, car runs lean..

Frank McCracken frankmccracken
Wed Jun 14 05:07:04 UTC 2006


Michael,
Could you please elaborate on o2 sensor placement? I have my 3 wire sensor
mounted facing up at about a 45deg angle.
Frank.


----- Original Message ----- 
From: "Michael Richards" <michael at fastmail.ca>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, June 13, 2006 9:23 PM
Subject: RE: [Diy_efi] O2 says rich, car runs lean..


> On Tue, 13 Jun 2006 21:01:40 -0700 (PDT), David Rowley wrote...
>
> O2 placement... The sensor needs to be mounted no lower than parallel
> with the ground. It must be before any cats and after any turbos. As for
> how much of the tip is directly in the exhaust stream I've never really
> found that much of a difference. You may be able to use a zip-cut wheel
> on a grinder to make your bung shorter if you think it's a big issue but
> that's dicy for getting a good seal afterwards and you will need to run
> a tap through the hole. A good quality M18x1.5 tap is expensive.
>
> -Michael
>
> > I was looking at the O2 tonight and the bung is welded on the outside
> > of the header collector.  It doesn't look like the O2 is sticking very
> > far into the exhaust stream.  If the O2 tip is not out into the
> > exhaust flow, would this cause it to give it rich reading?  I put a
> > DVM on the O2 (with the negative lead attached next to the O2 sensor)
> > and found that when cold, the O2 sensor voltage measure about .450
> > volts.  As it heats up, the voltage increases to about .875 volts.  If
> > I introduce air (undoing the PCV hose), the reading does not change.
> > I tried this again with another new O2 sensor and got the same result.
> >
> > Is the O2 tip somehow shielded from the exhaust flow causing it always
> > read rich?
> >
> > Thanks,
> >
> > Dave
> >
> >
> > Daniel Nicoson <A6intruder at myo-p.com> wrote:
> > The local parts guy won't have this device.
> >
> > The wide band sensors being referred to that also have NB output are
> > aftermarket units that have their own controller circuit (box).
> >
> > All wide band sensors have their own corresponding control circuit.
> >
> > Google "Wide Band O2"
> >
> > You should see most of the offerings with that search.
> >
> > For a very good technical discussion of all the considerations of NB &
> > WB systems, find the Megasquirt web site and look for their
> > dissertation on the subject of oxygen sensors. Pretty involved the way
> > those guys do a project.
> >
> > Happy reading.
> >
> > Dan Nicoson
> >
> > -----Original Message-----
> > From: diy_efi-bounces at diy-efi.org
> > [mailto:diy_efi-bounces at diy-efi.org]On Behalf Of David Rowley
> > Sent: Monday, June 12, 2006 11:48 PM
> > To: diy_efi at diy-efi.org
> > Subject: Re: [Diy_efi] O2 says rich, car runs lean..
> >
> > First al all, I want to thank everyone for their inputs. I very much
> > appreciate the help.
> >
> > I have never heard of a wide band O2 that also has narrow band output.
> > How does this work? Are there two different wires to select from for
> > output? Under what part number and whom would I find one?
> >
> > I like the idea of trying this, but I have no idea how I would explain
> > what I want to the local counter person at the car parts place.
> >
> > Thanks,
> >
> > Dave
> >
> >
> > Michael Richards wrote:
> > On Sun, 11 Jun 2006 15:45:28 -0700 (PDT), David Rowley wrote...
> >
> > First of all I have to say that tuning with a narrow band O2 sensor is
> > useless. I've been tuning for almost 7 years not and have to
> > constantly educate people about the inaccuracies of narrowband
> > sensors.
> >
> > Second, your readings may be related to the position of the O2 sensor.
> > If you overheat a narrowband they will frequently read rich when in
> > fact you're running lean. This too can sometimes be caused by an
> > ignition timing issue too much retard will over heat the sensor as
> > well. If you accidentally put it after a cat then that too will cause
> > incorrect readings.
> >
> > My suggestion is to replace the narrow band with a wideband that also
> > has a narrow output. This way you can have a proper temp-compensated
> > and accurate O2 reading converted to narrow band plus have a proper
> > mixture display on the dash. The 383 should like somewhere in the 13:1
> > under power and should run just fine in the low 15's under cruise. If
> > you properly balance all 8 cylinders with a pyrometer you can run it
> > leaner without any ill effects for fuel economy.
> >
> > -Michael
> >
> >> I have a chevy 383 motor with Vortec Heads, GMPP hot cam (218-228
> >> duration, roller), Edelbrock RPM Air gap manifold and a Holley 670
> >> throttle body injection unit.
> >>
> >> I have a problem where the car runs and idles great, until it goes to
> >> closed loop mode. When this happens, the ECM starts leaning out the
> >> AFR (the block learn goes down the minimum, 108 in this case) to the
> >> point where it will barely run. Why is the O2 seeing a rich mixture
> >> when it appears it is not? I have tried two O2 sensors with the same
> >> result. Does it have to do the the cam duration and manifold type?
> >>
> >> I have tuned a few vehicles and I have always been able to rely on
> >> the O2 sensor ( with the Integrator and BLM numbers) to get them to
> >> run right, until now.
> >>
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