Closed/Open Loop

[Michael Skolones]

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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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