Closed/Open Loop

[sfg]

Michael Skolones wrote:
> 
> My Volvo LH-Jet runs in open loop only when the engine is cold (i.e., before the
> O2 sensor warms up sufficiently to operate) and when the throttle is wide open.
> All other operating conditions are closed-loop.  I doubt that it varies much by
> manufacturer, but closed/open considerations probably vary by system type (i.e.,
> Bosch LH Jetronic vs D-Jetronic vs GM TBI vs modern sequential GM vs Holley
> Pro-Jection, etc).  I think the open-loop mode probably uses a stored "fuel map"
> on most systems, though it might be a pretty crude map on some older systems.
> 
> Regarding the O2 sensor, the signal on my LH-Jet varies from low to high with a
> period of about a half-second at idle; though the ECM might be reading the O2
> signal more frequently than this, at least the correction occurs at this rate.
> 
> I'm not sure what you mean by "everything possible".  The ECM is designed to
> modify the fuel injection pulse width and/or frequency in response to inputs
> from the throttle position, temperature, air flow or manifold pressure, exhaust
> O2, etc.  It is quite easy to overwhelm the ECM by unplugging a vacuum line or
> inducing some other fault.
> 
> Mike Skolones
> 
> ______________________________ Reply Separator _________________________________
> Subject: Closed/Open Loop
> Author:  diy_efi at coulomb.eng.ohio-state.edu at Internet
> Date:    10/3/97 4:49 PM
> 
> 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....
> 
> 
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> Subject: Closed/Open Loop
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I gave my old 286 laptop job security with Diacom software. I watch my
'87 TBI 350 Blazer all the time since laptop lives in the car. 
I see Open loop always when cold. Can't say I've looked at WOT....I'll
check for you....sfg
K5=