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

[David Rowley]

I have the O2 in header collector (long tube headers) and there is no cat.  Where should it be placed?  Where are the bad places to put it and why?  How would you go about balancing the cylinders?
   
  Thanks again,
   
  Dave
  

Michael Richards <michael at fastmail.ca> 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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