Peugeot XUD (1.8 and 1.9)

PSA's indirect-injection diesel — 1.7 as the XUD7, 1.9 as the XUD9 — and one of the most widely borrowed engines of its era. Beyond the 306 and 405 it went into the Suzuki Vitara and Baleno and the Hyundai Lantra, so a fault documented on a Peugeot describes those cars exactly.

It is famously long-lived and famously slow, and the durability is what makes the rest matter: these engines routinely outlast the vehicles around them, so the question on any example is what has been done to the fuel system rather than how far it has gone.

Which injection pump it has decides most diagnoses. The Lucas/CAV pump is the weak one: it wears internally and sheds fine debris into the fuel, which then blocks injectors and can take the replacement pump with it. A rough-running XUD with a Lucas pump wants the whole fuel side cleaned rather than one part replaced. The Bosch pump is the more durable of the two and fails less dramatically when it does.

It is an interference design, so a snapped belt bends valves — and on an engine this old and this cheap, belt history is the thing most often unknown and least often assumed.