The fuel efficiency on my 99 Nissan Almera 1.6L MTX has always been a bit below what I would expect, and the idle has gotten a bit rough lately, so I started poking around with a scope to see what I could figure out. I recently replaced the O2 sensor, and I noticed that at idle it was pegged lean, even though there was no evidence of any vacuum leaks. After a bit more poking around I noticed that the O2 signal was actually all over the place at idle, and that revving the engine for 10-15 second could force it into a different state. These are all at 500ms/div and 200mv/div.
For example here it's pegged rich with fast oscillations:
And here it's pegged low with oscillations:
You can see how there is an overall pattern of lean / rich fuel control going on but with breaks / oscillations in the larger curves.
And even when revving the engine at high speed I can see quick oscillation in the larger fuel control oscillations like those circled:
Since the spark waveforms looked fine I looked at the injectors voltage waveform and what I saw looked like a closing pintle bump that is jumping around between two spots almost constantly. These are 1ms/div and 10v/div. Sometimes it's like this:
And often it moves off to the right like this and would be almost indiscernible if it wasn't for the small voltage spike:
The thing is that this is really the first time I've looked at something like this and I'm not even sure it I'm actually looking at the closing pintle hump or not. Also, when the radiator fan comes on the pintle hump stabilizes in the first position.
All four injectors exhibit this waveform behavior and I've read that this indicates sticky / dirty injectors which may need replacing.
However, since I lack experience, I'm not sure if what I think I'm seeing is actually what I'm seeing, why the rad fan coming on would stabilize the pintle hump, and whether or not there may be some other explanation for the crazy stuff I'm seeing on the O2 sensor at idle.
I don't currently own a low current amp probe, so I can't check the when the pintle is opening.