although full service was inaugurated on 15 august 1978, within a month the emu100 units had been temporarily sidelined due to air conditioning trouble and various component issues. the 50-ton motor power coach (50ep100), which contained the 25 kv ac main transformer, was too heavy and caused bogie suspension stress issues, and was a safety concern when operating at high speeds. after four month of intensive troubleshooting involving tra mechanical section and the original equipment manufacturers, the vehicles were re-launched on 2 january 1979 in revenue passenger service. it was not until 1 july 1979, when the west coast mainline electrification project had reached substantial completion throughout its entire project length, had tzu-chiang been able to reach its full potential of operating at 120 km/h. taking 4 hours and 10 minutes between taipei and kaohsiung, the emu100 broke prior service speed records set by the "white steel train" dr2700 diesel multiple unit operating as the kuang-hwa express, and became tra's newest-generation premier express.