Volkswagen R5 TDI (2.5 five-cylinder)

Volkswagen's 2.5 five-cylinder TDI — in the Transporter T5 and the Touareg.

It is a unit-injector (Pumpe Düse) engine, which is the distinction that decides its diagnosis: there is no common rail and no rail pressure to read. Each injector contains its own pump, driven off a dedicated camshaft lobe, and injector faults are mechanical and cylinder-specific.

⚑ Its defining problem is the camshaft and the injector rockers. The extra load of driving the unit injectors wears the cam lobes, and the failure presents as rough running and poor starting rather than as a noise. On a high-mileage T5 it is a standard inspection rather than an exotic diagnosis, and the wear is visible with the cover off.

The EA188 four-cylinder PD engines share the principle and have their own page here; the injector and camshaft story is common to both.

A five-cylinder is inherently unbalanced in a way that requires a balance shaft, and its characteristic sound is not a fault.