The 1989–1993 5.9L Cummins engine kicked off the 12-valve legacy. This inline-six diesel uses a mechanical VE rotary injection pump for simple, reliable fuel control. It has a cast-iron block, a forged steel crankshaft, and strong internals built to last.

Known for its durability and easy upgrades, this engine is a favorite for towing, off-roading, and performance builds. It delivers solid, no-frills power and is easy to work on.