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
Message
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)
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