[4][5][6] 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.

During the new lunar year holiday period and other times of peak travel demand, EMU100 could be worked as a consist of three units (total of 15 coaches) per train.

However, as it is a multiple unit trainset with cabs at both ends, there is no important distinction between front and rear in normal operations.

After the occurrence of Touqianxi level-crossing accident, Taiwan Railway changed the front of the car to orange and yellow warning colours (locally known as "owl colours") to remind pedestrians and vehicles ahead to pay attention and not to attempt to cross tracks when the crossing lights are activated.

Due to the long dwell time from passengers getting on and off the train with a single door and the large amount of space occupied by the floor-mounted integral air-conditioning unit, all types of electric trains introduced by Taiwan Railway subsequently have had modular air-conditioning installed on the roof.

However, due to poor operational performance (it was not well-patronized), the business class trial service was terminated on March 31, 1992 and the ET100 vehicles were converted back to the original configuration.

The various Tzu Chiang Tokkyu trains purchased by the Taiwan Railways subsequent to the EMU100 were not generally regarded as quite as comfortable or luxurious as the EMU100.

At that time, Taiwan Railway was in the process of slowly metamorphosing from a premium intercity service to mass transportation.

Due to challenging terrain or traction equipment failure, EMU100 in later years often needed to be pushed by auxiliary pusher locomotives.

For one EP100-type vehicle, the EP112, because several of the ED100-type was written-off after level crossing accidents, the pantograph of EP112 was removed and the number was changed to 50EPD112, allowing EPD112 to be marshalled in place of one of the scrapped ED100-type trailers.

In 2009, in order to commemorate EMU100 being withdrawn from the regular service, the four cars 50EP108, 50EP111, 40ED105, and 40ED106 were painted with the original livery, without the "owl" warning stripes.