Well, if anyone'* interested, here'* what I learned yesterday.
The '93 factory shop manual'* code 44 diagnostics showed a 3-wire o2 sensor and had no mention of replacing the sensor itself
. I know for a fact that my '92 and '93 both have a 1-wire sensor.
So I looked in the '92 factory shop manual'* code 44 diagnostics, and it showed the correct 1-wire sensor and mentioned the replacement of the sensor.
I disconnected the o2 sensor and measured the voltage to the connector while the engine was running. It measured 390 mV, and this is within the expected range as per the diagnostics, so the ECM signal and ground reference were ok.
Then I reconnected the o2 sensor and measured the voltage again, while the engine was running and the sensor was at normal temp (hot). The voltage fluctuated slightly between 220mV and 400mV or so. So the ECM was correct in reporting the lean error.
I went to replace the sensor and found that it wasn't threaded tightly into the exhaust manifold! Since I was going to replace it anyway, I did that and measured the voltage again. Now the voltage fluctuated quite a bit between 300 mV and 850 mV or so.