4-Wire Oxygen Sensor Installation & Info
Here's the info from the Dealer Alternative site:
A
lot of people are reporting good results from substituting a three (or preferably
four) wire 02 sensor. Having a heater on the sensor maintains a consistent voltage
output, even at idle. This can make idle tuning a lot easier and more consistent.
A four wire sensor adds a signal ground wire along with the heater, again, aids
consistency. Hook the sensor signal ground wire (gray wire) to the ground wire
on the back of the head (the one the modified ecu ground goes to). The two white
wires are power and ground. Polarity doesn't matter on these two. Do not hook
the white wire ground to the same ground point you used for the gray wire, use
the white ground connector under the brake booster. The +12 white wire can be
hooked to the blue connector up on the driver's fender (the one you usually
hook your timing light to). Bill Clifford reports that a Borg-Warner OS126 from
Pep Boys is cheap and effective. We are now carrying a Bosch four-wire sensor
for $59.95.
We highly recommend a four wire oxygen sensor retrofit on the 1.6 Miatas (1.8 already has it) to get more consistent autotuning results and more accurate fuel mixture readout, especially at idle. A four-wire sensor adds a heater and a signal ground to the system. At idle, a single wire sensor may cool off below its optimum 600 degrees. It will still be giving readings, but they may not necessarily bear any semblance to reality. The heated sensor will also get online faster on start-up.