A fast transverse instability with beam loss has been observed in the 800-MeV Los Alamos Proton Storage Ring (PSR) when the injected beam intensity reaches 2 to 4/spl times/10/sup 13/ protons per pulse. Previous observations indicate that the instability is most likely driven by electrons trapped within the proton beam. Theoretical study has shown that beam leakage into the inter-bunch gap leads to electron trapping. Recent experiments were carried out by using the newly installed "pinger" and by varying the machine transition gamma to explore further the "e-p" instability and the nature of the instability. This paper summarizes some of these recent experimental results and theoretical studies.<<ETX>>