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Message
Rusty, the O2 sensor in itself does not
cycle, but only in response to changes in the oxygen content of the
exhaust. The reason that "cycling" is seen in automotive applications is
the EFI CPU of the auto is "hunting" for the optimum ratio for emissions approx
14.7 air/fuel ratio. So if it senses too high an oxygen contents (varies
from 0.45 volts or thereabouts to 0.0 volts) it increases the fuel content which
likely overshoots the desired ratio so then the computer senses this overshoot
through the o2 sensor and so quickly corrects the mixture by decreasing the fuel
content. This seesawing between over and under the desired voltage (approx
0.45) causes the O2 sensor to send out a "Sawtooth" wave form of voltage varying
from under 0.45 volts to over 0.45 volts and under certain conditions and
probably approach 0.0 to 1.0 volts in swing.
In the automobile use Lead will quickly decrease
the sensitivity of the O2 sensor to the point that it is relative useless for
the emission control purpose since it is trying to maintain an optimum by
quickly sensing and responding to an over or under oxygen voltage signal.
In our application we more or less use it as a trend indicator Rich, Lean, Going
Rich, Going Lean. Millisecond response time is not required for our
reaction time {:>).
In our use, the O2 sensor simply sends out a
voltage proportional to the O2 content it sees and since there is no computer
feed back it stays relative stable (unless you change an engine parameter or
mixture) or changes slowly.
Ed Anderson
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
Sent: Friday, April 02, 2004 1:31
PM
Subject: [FlyRotary] Re: Rusty's O2 / EM2
problems.
Rusty,
>>... A properly functioning oxygen sensor
will show a
>> rapidly fluctuating output voltage between
approximately 0.1 and 1.0 volts.
>> The time taken for the voltage to
change from 0.1 V to 1.0 V (referred to as
>> the lean to rich
response time) should be about 300 milliseconds. A similar
>> time
should be measured when the voltage changes from 1.0 V to 0.1 V
(rich
>> to lean response time).
>
> Can anyone
explain why the voltage is supposed to cycle between .1V and 1.0V
>
? Tracy said the EM-2 doesn't do any averaging, but just captures
the
> voltage in a snapshot when it's time to measure that
channel. If that was
> the case, it would seem that a "properly
operating" sensor would cause the
> EM-2 to be erratic.
It *really* depends on the EM2 sampling rate. I
would
hope that in 300 mS, the EM2 would have taken at least five
samples, but maybe not ...
The O2 cycling is due to
the processing delay of the
computer; the sensor gets read, and the
computer sees
that the engine needs more (or less) fuel, so it adjusts
the injector timing; by the time that that particular
expended charge
gets to the O2 sensor, the computer has
taken more readings, inducing a
small amount of "overshoot".
Then, seeing that, it compensates in
the other direction.
As long as it stays in the range that produces
more than .1v
and less than 1.1v, the engine judged to be running
efficiently. Ideally, at a stable RPM, the oscillations
would
"settle" to somewhere near the middle of the range,
but processing delay
assures that this is all but
impossible.
That's my understanding
...
Dale R.
COZY MkIV #1254
Considering that my O2 sensor exhibits similar behavior as yours
and I also measure downstream EGT temps (after turbo) right beside the O2
sensor and only see temps in the 700F range, I can't help but think that maybe
the low temps are possibly the cause of the problem.
My EGT probes are about 10 inches from the port, and the
O2 sensor is about 40 inches farther downstream. I'm confident
that I can get the temps to 800F at the O2 sensor, but I may not have the
day I installed the sensor. I was seeing temps in the 1000 to 1100 range
at low rpms, but the other day, when tied down, I was reaching 1600's at
full throttle. That was with the old sensor though. I'll probably
be doing some more running tomorrow, so we'll see what I get. I also
have the old mixture gauge installed as well as the
EM-2.
Here is an excerpt from that
site:
How To Test Oxygen
Sensors?
Using an appropriate connecting device, connect the
sensor output to your oscilloscope; do not disconnect the sensor from the ECU.
Run the engine at approximately 2000 rpm. A properly functioning oxygen sensor
will show a rapidly fluctuating output voltage between approximately 0.1 and
1.0 volts. The time taken for the voltage to change from 0.1 V to 1.0 V
(referred to as the lean to rich response time) should be about 300
milliseconds. A similar time should be measured when the voltage changes from
1.0 V to 0.1 V (rich to lean response time).
If the sensor output is
constant or the response time is too slow the sensor should be changed.
Can anyone explain why the voltage is supposed to
cycle between .1V and 1.0V ? Tracy said the EM-2 doesn't do any
averaging, but just captures the voltage in a snapshot when it's time to
measure that channel. If that was the case, it would seem that a
"properly operating" sensor would cause the EM-2 to be erratic.
Hopefully, tomorrow's testing will reveal some more
useful info.
Rusty (looking to fly again this
weekend)
>> Homepage:
http://www.flyrotary.com/
>> Archive:
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