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

["Dan Bocek" <dan@di.com>]

> 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?

As soon as the full throttle switch closure is detected (well, actually
it's more like a 3/4 throttle switch) the engine does indeed go into
an open loop mode.  At that point, it indexes a lookup table and outputs
a value to the frequency valve which is appropriate for the current
RPM and boost pressure.
-- 
                                                   
                                                    Dan Bocek
                                                    dan@di.com