You can see the injector pulse width change in closed loop but the changes are small. You will have to set the scope up with a lot of time on the screen, with maximum samples, so you can capture the injector and the O2 over enough time to see a couple of O2 cycles. You will also need to deploy some resolution enhance to the O2 signal to clean up some of the noise on that signal so you can see it clearly.
Then you can zoom in and use rulers to measure the IPW when the O2 is high and compare to when it is low. Then you will see the difference.
THE PicoScope Automotive Authority
In North America