The PCM controls the ground side of the injectors. You would need to find out when there is no pulse, if you are loosing power or ground. A likely cause IS the PCM. We have had problems on the Cavalier where water gets into the connectors and into the PCM itself. It's pretty obvious, very corroded. There was actually a recall on these where we inspect the PCM for corrosion and add a shield to water out of it.
Thanks! We will check this and I will let you know what we find.