Fw: Justa O2 Note

[EFISYSTEMS at aol.com]

In a message dated 98-10-13 10:13:47 EDT, you write:

<< Subj:	 Fw: Justa O2 Note
 Date:	98-10-13 10:13:47 EDT
 From:	nacelp at bright.net (Bruce Plecan)
 Sender:	owner-diy_efi at efi332.eng.ohio-state.edu
 Reply-to:	diy_efi at efi332.eng.ohio-state.edu
 To:	diy_efi at efi332.eng.ohio-state.edu
 
 May have been overheard at the grocery store this am.
 Bruce
 
 >->My understanding of the chemistry is that it has to go lean so there is
 >->excess oxygen that the catalyst picks up, then rich so it can use that
 >->oxygen to take care of the HC and CO.  It has to average stoichiometric
 >->to keep things in balance.
 >-
 >-I'd always assumed that because they're using a cheap narrow-band o2
 sensor
 >-who's output right *at* stoch is a bit uncertain, they just compensated by
 >-jumping across the boundary a lot, with the thinking that they'd get
 >-"pretty close" to stoch on average.
 >
 >They may have started using this control strategy due to the limitations
 >of the narrow-band oxygen sensor, but now they definitely cycle back and
 >forth to keep the catalyst happy.  The excursions are very small, but they
 >act in conjunction with the oxygen storage capability of the catalyst to
 >allow a balance between oxidation of HC and CO, vs reduction of NOx.
 
 
 This is very true,,,I just spent the last six days datalogging a 99 chev
truck and have seen the AFR vary from 14 - 15:1 while in closed loop and is
intentional to reoxygenate the exhaust stream to further burn HC's since air
pumps would mess up the O2 sensors.....
-Carl Summers