O2 sensor in SPICA car

["Rich Hirsch" <rhirsch@domain.elided>]

Hi Tim,

>> I would like to put an O2 sensor in my '74 spider to aid in tuning
air/fuel
mixture. For convenience, I would like to use a 1-wire sensor. I took a look
underneath and I'm not sure where would be the best place to mount the
sensor.
The car is still using the OEM 4:2 exhaust manifold. <<

My '78 Spider has a Shankle header. I mounted an O2 sensor near the first
bottom bend
after cyls 2 & 3 come together. I mounted the probe in an anti-fouling 18mm
spark plug adapter.
I just cut off the bottom of the adapter and brazed it onto the pipe. Mount
the probe so it doesn't
point down or you might hit something with it.

I wouldn't use a 1-wire sensor. Use a 3-wire sensor (with heater) instead.
If you don't, you really do
have to worry about where to mount it, as it's only accurate within a
certain temp. range.
I don't think the cost diff between a 1- and 3-wire sensor can justify the
1-wire sensor.
The output from the sensor goes to a (0-1.99v) digital voltmeter I have
mounted in the car. Stoich. is
about 0.5v for the probe, but my meter usually reads from 0.9v - 1.0v at
idle or under power (rich).
When the accel. pedal is released, the voltage drops to less than 0.1v
briefly due to the fuel cutoff switch
(lean) working as expected. It is very sensitive. I've had it installed for
about four yrs now.

Due to the nature of the O2 sensor, you'll never see stoich. (0.5v) for long
as the graph of
probe voltage vs. percent O2 is very steep at stoich--see Bosch,
"Automotive Electric/Electronic Systems", 2nd edit., p.120.

Rich Hirsch
St Louis MO

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