Oxygen sensor gauge reading at wider throttle openings

[markweatherill]

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.

[SVOboy]

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

[markweatherill]

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.

[dcb]

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.

[markweatherill]

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