Hydrogen ICE can achieve carbon neutrality and is adaptable to medium and heavy-duty vehicles, for which electricity is not always a viable option. It can also be developed using high-quality conventional diesel/gasoline engine technology. Furthermore, it allows for the conversion of existing engines to hydrogen ICE, making it highly marketable. The reliability and durability of MPI hydrogen ICE is better than that of DI, and MPI has an advantage over DI in terms of cruising range because the low-pressure injection of hydrogen reduces the remaining hydrogen in the tank. Improving MPI output is, however, an important subject, and achieving this requires suppressing abnormal combustion such as pre-ignition. In this study, an inline four-cylinder 5L turbo-charged diesel engine was converted to a hydrogen engine. Hydrogen injectors were installed in the intake ports and spark plugs were installed instead of diesel fuel injectors. A two-stage turbo system was adopted to improve the engine output as turbocharging is required for MPI hydrogen engines in a wide range of engine speeds. The effect of piston combustion chamber shape, compression ratio, valve timing, and injection timing were optimized. As a result, the engine achieved 2MPa BMEP and 103% of the low-speed torque of the base diesel engine. Finally, the medium-duty truck using the newly developed hydrogen ICE was also presented in this paper.