Some history:
Silverliners were used from the PRR era (Amtrak did not take over the service until 1972, incidentally) until around 1978, when Amtrak rented Jersey Arrows for the Clockers and Silverliner Service. The Arrows were returned to NJ beginning in late 1980; the Metroliners (branded as Capitol Liners) - which a decade before had been determined unsuitable for Harrisburg service - took over in 1981. As the Capitol Liners began to increasingly fail in the mid 80s, they were pulled by AEM-7 locomotives (and sometimes E60s) on many runs, with the pantographs up for hotel power. Locomotives were assigned for all runs starting January 25, 1988 (which included ten minutes added to the schedule due to the slower E60s).
But, the wreck of the Night Owl on January 29 took two toasters out of service, and Amtrak assigned F40s with no Suburban Station service on February 1. Although Amtrak had wanted to fully dieselize the line for several years, E60s were re-added within a few days, though 30th Street remained the terminal. Some of the E60s and Capitol Liners were modified for push-pull operation in 1988, with plans to convert them to HEP. By mid-1988, the line had a motley assortment of electric and diesel power used; modified Capitol Liners were used as cab cars
Unfortunately, my primary source for this was published in 1988, so what happened after that isn't clear. I'm not sure when Amfleets replaced the Capitol Liners as coaches, nor when electric service ended entirely.