Mitsubishi 4D56 (4D5 family, 2.3 and 2.5)

Mitsubishi's 2.5 diesel — the engine of the L200, Pajero and Pajero Sport for thirty years, and one of the most widely copied and licensed diesels in the world.

Its defining failure is the balance shaft belt, and it destroys engines. A second, smaller belt drives the balance shafts behind the timing belt. When it fails it does not simply stop working — it gets drawn into the timing belt, which then jumps or breaks, and on an interference engine that is the end. Many owners and workshops delete the balance shafts for exactly this reason, and on any 4D56 the first question is whether that belt has been changed with the timing belt or removed altogether. A timing belt done without the balance belt is the shape of the failure, not a saving.

The later common-rail DI-D versions add injector trouble. They are sensitive to fuel quality and to injector seal condition, and a rough-running DI-D is very often the injectors or their seals rather than anything mechanical.

Beyond those it is a simple, slow, extremely long-lived engine that is still being built under licence — which is why a fault documented on a 1990s Pajero describes vehicles far newer and far away.