O2 Sensor Open/Close Loop

[Robert McElroy]

	Well, I have been listening for awhile, and have read many of the =
previous posts about O2 sensors, so I'll add my opinion as long as you =
remember it is worth only as much as you paid for it.

	Most O2 sensors are accurate over only a limited range of A/F ratios =
(actually they are very nonlinear once you start moving away from =
stoich., and thus it becomes more difficult to get an accurate value for =
A/F ratio.)  When your engine is accelerating hard (many ways to sense =
this, one indication of which is WOT), the actual A/F ratio is closer to =
(actual A/F ratio varies greatly) 13:1 than 14.7:1 (stoich.)  Besides, =
the primary use of an O2 sensor (in most of the systems that I have =
examined) is to provide better part-throttle gas mileage and reduce =
part-throttle and idle emissions that occur due to non-stoichiometric =
A/F ratios (CO, NOx, etc.)

	The reasoning is that most street engines are at idle and part-throttle =
for the overwhelming majority of their operation.  Therefore, cleaning =
up the part-throttle and idle emissions and improving the part-throttle =
gas mileage would yield the greatest benefit.


My ECM is in closed loop mode at idle and part throttle. At wide open
throttle is goes into open loop mode ( it stops reading the O2 sensor ). =


WHY?

Mark Mason.