The Metroliner cars, worn out from nearly two decades of heavy use, began to fail frequently. In April 1985, Amtrak began studying the possibility of removing electrification west of Paoli. On-time performance decreased from around 85% in 1985 to below 60% in early 1988. On January 25, 1988, Amtrak began towing the Metroliner cars with AEM-7 locomotives rather than running them under their own power, although the cars had their pantographs up to power lighting and heating systems. A wreck of the "Night Owl" four days later two took AEM-7 locomotives out of commission, exacerbating a shortage of electric power available to Amtrak. On February 1, Amtrak converted all "Keystone Service" trains to diesel power and terminated them on the lower level of 30th Street Station, as diesel-powered trains were not allowed in the tunnels to Suburban Station. The change was listed as "temporary" on timetables starting on May 15, 1988 and lasting into 1990. After dieselization and the lengthening of schedules, on-time performance jumped up to consistently over 90%.