You have an air leak somewhere and they can be very difficult to fine, very close inspection of all the joints is requirded. Regards Peter

If you leave it parked facing steeply downhill you may find that the fuel will leak out where the problem is.

There appears to be no leaks

The old non commonrail diesels had a transfer pump in the injection pump that pulled the fuel from the tank by vacuum, I think the original idea was to stop the smell that early diesels had because of leaks. The early Hdi's had a pump in the tank but I believe some have now gone back to the vacuum system which is why leaks are difficult to find as the system is under vacuum while running, which is why I suggested parking it on a slope, to create some pressure.

If the fuel filter needs replacing that will add to the problem and its very often in that area the air gets in.