Skoda Fabia 1.9tdi, ATD engine

hello good.

I have a problem with a Skoda Fabia 1.9 TDI, ATD engine. The car is normal and when you start it hot it costs two or three times more than normal time to start.
I have checked with diagnosis machine and gave a camshaft sensor failure, which is solved and has not reappeared.
After repairing this and checking that I kept failing I have proven the usual things, without finding any failure.
I have tried changing pieces that usually fail such as drums, starter engine, injector joints, Tª sensor, etc. And the failure persists.
I have checked the signals of the spinning captors with the oscilloscope and are correct, as well as those of the injectors.
The truth is that it is no longer occurred to me to check.

If someone has happened to him, something similar would be so kind to tell me that it could be what fails.

All the best.