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

[David Rowley]

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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