Space charge formation processes were investigated on silicone and acrylic elastomers by the pulsed electro-acoustic (PEA) method. Homo charge injection was observed in silicone as anticipated on one hand. Hetero charge injection was unexpectedly observed in acrylic elastomer on the other hand. This peculiar behavior might be related to material composition and additives. Multiple successive hetero charge injection and even homo and hetero charge double injection were observed in the acrylnitrile and acrylic elastomers used. A multiple injection process is interesting to be explored further. Hetero charge injection is an apparent phenomenon that needs more theoretical consideration.