weird o2 sensor readings? (mc'd urq)

Sun Jul 6 22:11:03 EDT 2003

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

     <<<->>>=<<<->>>=<<<->>>=<<<->>>=<<<->>>=<<<->>>=<<<->>>
The solution is obvious.  We all have to become dumber. -Jon Rappoport

So crucify the ego, before it's far too late
To leave behind this place so negative and blind and cynical,
And you will come to find that we are all one mind
Capable of all that's imagined and all conceivable. - TooL, Reflection
      <<<->>>=<<<->>>=<<<->>>=<<<->>>=<<<->>>=<<<->>>=<<<->>>