Iesel engine. but most of it is operating manually. maintenance and repair centers mostly have used the manually device which depended on the hand of operator to operate it therefore there are inaccuracies in tests. The injector tester device was modified from manual operation to mechanical operation to achieve the uniformity of the injection pressure during the injector test. https://www.roneverhart.com/Western-Digital-Ultrastar-DC-HC550-WUH721816ALE6L0-0F38460-16TB-7-2K-RPM-SATA-6Gb-s-512e-ISE-3-5in-Hard-Drive/