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

[Daniel Nicoson]

Regardless of the tangent this thread took on WB vs NB, I'd like to thank
Tom for a great post on troubleshooting narrow band sensors.  Many of us
still have to meet smog and although I use a DIY-WB for my WOT tuning, I
depend on proper operation of my NB sensors to tune for smog at the low
power area's of operation.

I have printed the information below to .pdf for storage on my own hard
drive for the day I have similar problems.  Hopefully I don't see that day
but if so I can recall if from my HD archives.

Thanks Tom.

Dan Nicoson

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of Tom Visel
Sent: Sunday, June 11, 2006 7:34 PM
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] O2 says rich, car runs lean..

Look at your oxygen sensor voltage, preferably with an oscilloscope,
though even a scan tool or a high-impedance DVOM would do, as long as it
doesn't do too bad a job of "smothering" away the sensor's natural
jitters with its averaging function.  Some meters that have a bar graph
at the bottom will let the bar graph twitch while the numbers get
averaged out to something smooth and useless.  A bar-graph ricer gauge
will do also; the cheaper ones are better for this purpose because they
let the original signal show through without cleaning it up for prime time.

What you are looking for is movement of the sensor voltage - is it
jittering rich/lean or rich/richer, or is it parked at some voltage?  If
it is parked at some rich (>450 mV) reading and staying there, odds are
the sensor is dead.  If it is reading over 1 volt, odds are you have a
bad ground for the sensor, and stray electrons are making their way home
on the oxygen sensor line.  This is more prevalent on vehicles with
headers, due to the gasket trickery that often makes for a less than
perfect ground at the flanges.  Heated oxygen sensors have even more
problems like this, because the 12 volts supplied to the heater needs
its own GOOD ground, and it will use whatever other wire is available if
the heater ground wire is bad.  This is more of a problem on fresh
custom builds and vehicles with older sensors.

To quick-test your oxygen sensor ground, unplug the alternator while
watching the O2S output.  Did it improve?  If so, bad ground.  More
electrical load = more strain on grounds.  Another method of testing is
to run a jumper cable from the battery negative post to the housing of
the O2 sensor to act as an extra ground.  If that improves the signal
quality, you know your grounds need work.

BTW, your oxygen sensor can be switching rich/lean at the sensor - going
from .25 to .75 volts, say - and a bad ground will turn that into a
signal that varies from .6 to 1.1 volts, which the ECM would interpret
as all rich, all the time.

HTH!
TomV

David Rowley wrote:

>Hi all,
>
>  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.
>
>  Has anyone out there seen anything like this?
>
>  Thanks,
>
>  Dave
>
>
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