Re: O2 sensor readout (Air/Fuel ratio indicator)

[rdh@genrad.com (Robert D. Houk)]

   > I have done some testing with a portable 4 - gas (O2, HC, CO, CO2) 
   ...
   On many cars, Audis among them, full throttle is a special sensed condition
   that disables the closed loop and provides enriched mixture for maximum power.
   On my 4000SQ, this is a microswitch on top of the throttle body.

I've often wondered about that -- the "sensor" (aka microswitch) feeds into
the engine computer. Does the computer truly go "open loop", or does it in-
stead switch its internal "target" closed-loop point? I.e., in true "open
loop" the computer would nominally switch the Freq Valve "off" (or "on", I
never can remember how many nested pressure actions and counter-actions are
going on out there), although it might instead simply switch to a pseudo-
"open loop" mode running the Freq Valve at 25% (or 75%, or ???). On the
other hand, if it stays "closed loop", then it would simply switch the "tar-
get" mixture setting, using the Freq Valve to maintain the desired WOT mix-
ture, say 13:1, rather than so-called-Ideal 14.7:1.

Anyone know fer sur?

					-RDH