Closed/Open Loop

[Shannen Durphey]

Corey & Alicia Beaverson wrote:

> Can someone tell me how often a particular efi system will go into
> closed loop on say, an "average" drive or whatever. Does it vary a whole
> lot from manufacturer to manufacturer? And when the system is in open
> loop,....is this when a stored fuel map is used to set the a/f ratio? If
> so, are there alot of different fuel maps stored in the ecu for varying
> conditions i.e. WOT, startup, cold engine and etc?
> On a different note,  when a system is in closed loop, how often does
> the ecu get a value from the O2 sensor on the "average system". Also is
> it safe to say that when in closed loop, the ecu will do everything
> possible to keep the a/f ratio at a predetermined value or not?
> Many thanks in advance....

  In my experience, closed loop occurs under different conditions even
between cars of the same make.  Older GM efi vehicles switched from open to
closed when coolant temp reaches 120 deg f, and 30 seconds has elapsed since
startup and O2 signal voltage varied from .59 volts by a certain amount.
Service literature says vehicles switch to open loop during WOT,  when
various sensors fail, and when O2 sensor stops sending voltage signals.
This latter condition depends on sensor position in the exhaust, exhaust
temperature, heated or non-heated sensor.  Older V8 engines tend to go out
of closed loop during any extended idle.

As emissions standards get tougher, cars will go into closed loop faster and
remain there longer.  '96 and newer GM has heated O2 sensors in three or
four positions. Even monitors misfires and catalyst activity.

ECM always uses stored fuel map to deliver fuel...uses O2 signal during
closed loop to adjust fuel delivery more or less than stored value.

Very safe to say ECM does everything in it's power to keep fuel at
predetermined level during closed loop.