weird o2 sensor readings? (mc'd urq)

[Todd Phenneger]

Michael,
  I have a similar problem but I have power when lean, it just
scares me to be leaning out.  My car will lean out for about 1/2
second when I floor it then it will go back up and the power
comes on.  If I push the accelerater smoothly over say 1-2
seconds to the floor it will not lean out and has much more
power than if I simply floor it.  I am suspect of my fuel pump
and will be re-checkign my statick Fuel Pressure again but am
not sure.  I have tried a couple differetn CIS units and all
have the same effect.
  ANyhow, I would call JC WHitney and order that Fuel PRessure
Tester or get one locally. :-)
  l8r
     Todd

--- "Michael S. Williams" <mike at borderlinemotorsports.com>
wrote:
> At 9:57 PM -0400 7/6/03, Nate Stuart wrote:
> >  > so, here's where the weirdness started... the display was
> showing
> >>  about .400-.600v at idle, and would drop quickly under
> load, to
> >>  almost zero....  so, i pulled over and turned the mixture
> screw about
> >>  1/2 turn clockwise (i know that's alot)... enough to cause
> the
> >>  frequency valve to shut off at idle... got back in the
> car, and at
> >>  idle, itwas reading about .800-.900v... ok... SEEMS
> closer... but
> >>  assoon as i got on the gas, it would drop...
> >
> >You cannot use a multimeter to tune a closed loop O2 system.
> The O2 sensor
> >voltage does not stay at a steady point, instead it
> fluctuates back and
> >forth very quickly from lean to rich readings, as the ECU
> adjusts the
> >mixture. I have yet to see a multimeter that
> refreshes/samples fast enough
> >to even come close to properly displaying an O2 sensor
> output, especially
> >under load/high RPM, where the cycle rate is very fast. Do
> not tune the
> >engine based on the multimeter readings. You're not going to
> be able to
> >ever get the 'correct' O2 reading this way, as the ECU will
> continually be
> >adjusting the mixture anyway.
>
> ok... i figured, though, that it wouldnt be jumping from 0-1
> volt
> constantly, but within a smaller range...  otherwise those a/f
> gauges
> would be going from blank to fully lit constantly...
>
> iwas under the impression that the voltage signal would start
> to
> stabilize a bit under load, hence the desire to have a .9-.95
> volt
> reading...
>
> >  > but here's the strange thing.  the car had a LOT more
> power, and the
> >>  reading dropped BELOW 0v, into 'negative' voltage, about
> -.02 or
> >>  so....  and finally, when i turned off the car, the
> voltage reading
> >>  stayed there, and was around .550v
> >
> >Yup, things like that will happen, it's usually because the
> meter is not
> >capable of measuring the fluctuating signal correctly.
>
>
> ok
>
> >
> >>  but, like i said, the power is closer to where it is
> supposed to be,
> >>  it isnt using coolant, the compression is almost exactly
> the same
> >>  across all 5 cylinders, the o2 sensor is brand new, the
> idle/wot
> >>  switch is new, the temp sender for the isv is new, the
> michelin man
> >>  hose is new, i checked and rechecked the intake hosing,
> inspected the
> >>  vacuum lines.....nothing....
> >
> >It may have been that you were running lean before, for some
> reason, so
> >your adjustments may have helped, but they are probably not
> where they
> >should be. Wait until you get that real A/F ratio gauge. At
> the very least
> >that will have a fast enough display to show you roughly
> where your
> >mixture lies.
>
> i understand it fluctuates, but i was also under the
> impression that
> the fluctuation was within a sub-range of the 0-1 volt
> reading, which
> is where stoich is, and that's where the a/f ratio gauges
> indicate
> green/blue/whatever
>
> >Also, double check the Bentley for the proper baseline
> >setting of the CIS system, it's really a lot simpler than you
> are making
> >it out to be.
>
> >  If I recall correctly you just need to measure the OXS
> >valve's duty cycle at warm idle, and turn the mixture screw
> until the duty
> >cycle falls within a specified range. It's been a while since
> I've ever
> >mucked with this (yay for programmable efi ;), so I may be
> way off of the
> >procedure, but it is in the Bentley. If you need I can dig it
> up sometime.
>
>
> trust me, i tried that.  i set it to be 'exactly' within specs
> of the
> bently at 50%  dc +-8%.  it had no power above 3k rpm. then i
> listened to listers advice that i had in the archive and set
> it at
> 35-40% for a richer mixture.  that helped a little, but not
> very
> much.  then i tried 20%, again, helped more, but not very
> much.  now
> it is somewhere around 4% pegged, because the frequency valve
> doesnt
> even turn on at idle it is so rich, and FINALLY im gettinga
> little
> bit of power...
>
> so there's something going on in there that i havent found
> yet...
> that's why it seems im making it more complex...
>
>
> >
> >>  the one thing i dont have on hand is a fuel pressure
> gauge, but im
> >  > gonna order one, since it seems like it's a good idea to
> have anyway,
> >>  esp w/ the cis....
> >>
> >>  anyone have any thoughts?
> >
> >Yeah, that definitely doesn't hurt to have with a CIS car, as
> everything
> >is based off of the system pressure.
> >
>
> yup...
>
> thanks for the advice...
>
> and i have read about the benefits of the efi, trust me, it's
> on my
> mind right now...heh...
> --
> MswmSwmsW
>
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> Rappoport
>
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