duty cycle readings ?

[Orin Eman]

We just have a little confusion as to how often the ECU adjusts the
duty cycle vs how often the O2 sensor signal changes.  The ECU will
adjust the duty cycle about 10 times a second.  Depending on how
old the O2 sensor is, it may well take several adjustments before
the mixture changes enough for the O2 sensor to respond.  I believe
SJM would have been talking about the O2 sensor signal changing
once or twice a second.
 
> in closed-loop, the duty cycle changes b/c the o2 signal is going up and 
> down. The rate of change for the duty-cycle is about the same as the change 
> in the o2 signal, although there is prolly some delay b/c of the ECU 
> electronics. So if the o2 sensor signal just happens to be bouncing around, 
> [which I know it does, I've seen it on an afr gauge], the duty cycle will 
> too...no problem w/ your ECU. In open-loop however the D.C. should be 
> fixed. If the o2 sensor is more than 30k miles old, I'd change it, or less 
> miles if you burn oil or have a rich mixture. Oil and rich mixtures build 
> up deposits on the sensor, making them short-lived. I think heated o2 
> sensors have a longer life, something like 60k for newer designs. That may 
> explain why you get a difference of in duty cycle frequency compared to SJM 
> info.

Usually, an old O2 sensor reacts slower than a new one, not faster.
So, in this case, I think it's just confusion about which signal
changes at which rate.

Orin.

> 
> 
> At 04:15 AM 12/16/2000 , you wrote:
> >Hi all.
> >I am posting this question 3rd time. No response yet. Hope never dies.
> >
> >According to SJM ECU changes duty cycle in closed loop 1-2 times per
> >second.  I see that duty cycle is changed much more frequently (10
> >times, maybe more). In DMM screen I see blur. I wonder is my ECU doing
> >wrong things? But it sweeps in spec: 45-50%. In several minutes it
> >shifted to 40-50% but it is another why?.
> >
> >OXS voltage mesured by DMM is between 15mV and 2.2V. Does someone has
> >any idea why it can be more than 1V according to spec? (I did not
> >disconnect OXS wire while measuring voltage).
> >
> >Do I need to plan OXS changing?
> >
> >Thanks.
> >
> >Konstantin Bogach
> >200tq 89
>