Oxygen sensor gauge reading at wider throttle openings
 

I have one of those O2 sensor gauges. It displays a light show of LEDs bouncing back and forth when the engine is running.
Well, at wider throttle openings and low vacuum, the gauge just goes out. At that point I notice a lack of power. In this vehicle it's typically when I'm trying to maintain speed on a hill. Easing off the throttle results in the power coming back and the LEDs come back on.
I guess the ECU is going into open-loop and using a lean fuel map (or something) but why would the O2 sensor appear to stop working?
Vehicle is a Nissan with the GA15DE engine by the way.

Is it a narrowband o2 sensor? If so, the gauge is basically meaningless. :)

The gauge only shows that the sensor is working, I realise I'm not going to get meaningful air/fuel readings off it. It was installed to replace a 1v voltmeter I was using before.
But it does show, by the lights all going out, that 'something' happens under the above mentioned conditions.
I guess I need to look at the injector pulses to see what they're doing. I have a vintage dwell meter but never hooked it up yet.

Well, the gauge is probably telling you that the engine is stuck on lean under high power demand, for some reason, so it isn't entirely useless :) Try a bottle of injector cleaner in the tank.

Could this be a bad fuel pressure regulator, I wonder, causing simple fuel starvation at very low vacuum?