Closed/Open Loop

[Mark Nowakowsky]

Hi Corey & Alicia,

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?

To the best of my knowledge a system will go into closed loop once the O2
sensor reaches about 600 F. During an "average" drive to work, the system
will stay in closed loop for the duration of the drive.  Only after an
extended idle will the system sometimes go into open loop and that's only if
the O2 sensor is a two wire (no heater) type. The three wire O2 sensor has
an internal heater to maintain 600 F + temperatures and will maintain closed
loop if exhaust temp goes below 600 F.  These are normally further down the
exhaust.


> 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".

On an average GM system a new O2 sensor will swing from one end of its range
to the other (.1-.9v) about 1-3 times a second.


> 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?
>

Yes, that's why it's a "closed loop" and  the ecu has total control over the
fuel and ignition systems.

> Many thanks in advance....

    (:



Mark Nowakowsky
mailto:mdnowak at connect.ab.ca
http://www.connect.ab.ca/~mdnowak/index.html