Volkswagen TDI (badge, not an engine)

TDI is a badge, not an engine — Turbocharged Direct Injection, Volkswagen Group's word for its turbodiesels since the 1989 Audi 100. It is on three to eight cylinders, on 1.2 to 4.2 litres, and across Volkswagen, Audi, Škoda, SEAT, Cupra, Porsche, Bentley and Dodge in this catalogue.

⚑ The badge spans three completely different fuel systems, and which one a car has decides almost everything about it.

• Distributor injection pump, the earliest, one pump feeding all cylinders.
• Unit injectors — Pumpe Düse, PD — from 2000. There is no fuel rail at all: each injector is its own pump, driven off the camshaft, so the camshaft and its followers carry a load an ordinary diesel's do not. Cam wear and the injector wiring loom inside the rocker cover are the PD's signature, and neither exists on the engines either side of it.
• Common rail, on the V8 from 1999 and on most of the range since 2009, with piezoelectric injectors.

So a part number, a fault code reading, an injector test or a service procedure quoted for "a 2.0 TDI" is worth nothing until somebody establishes the year, and the two systems have almost no parts in common.

⚑ The EA189 is the emissions-scandal engine — around eleven million cars — and it matters diagnostically rather than legally: a recalled car is running different software from the one it left the factory with, so its behaviour, its regeneration intervals and much of what is written about it online describe two different cars.

The designation is what to establish, and it is on the engine and in the build sheet. The families this catalogue carries under this badge — EA188 (the PD 1.9 and 2.0), EA189, EA288, the EA896 and EA897 V6s, the EA898 V8 and the R5 TDI five-cylinder — each have their own page here, and the differences between them are the ones that matter.