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Re: O2 sensor, now Frequency Valve info

RDH asked
> I've often wondered about that -- the "sensor" (aka microswitch) feeds 
> into the engine computer. Does the computer truly go "open loop",TEXT > 
> "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 
> "target" mixture setting, using the Freq Valve to maintain the desired
>  WOT mixture, say 13:1, rather than so-called-Ideal 14.7:1.

>Ned said,
>Full throttle gives a fixed duty valve reading of 64% if memory serves.
>Cold running is slightly higher.

>>Dan Bocek said
>>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.

I checked the frequency valve duty cycle at full throttle and as Ned 
indicated it is around 65%  Negative Duty cycle. At idle the duty cycle 
normally cycles between 45 - 55 % but if you create a vacuum leak by 
pulling out the dipstick the duty cycle changes to 80% to compensate for 
the lean condition. I once found some cracked crankcase breather hoses 
on my 86 5000CST when I was testing out an oscilloscope and noticed the 
duty cycle was over 90% at idle. The O2 sensor readout was also pegged at 
the lower limit (0.1V). 
Scott M.