Golf MK5 2.0 TDI crank but not start, if start no problem, help
 

Hi, I'm Federico and I have a Golf MK5 2.0 TDI and I have a problem that haunting me for a couple of years. I tried practically everything with my mechanic but we could not solve the problem.
I hope some of you help me.
This is the fact:
The car (when it start) run perfect, no problem in the engine or elsewhere, I've done a lot of km with no problem.
If the engine start in the morning there is no problem, I can run the car all day with many stops and the engine always start without problem.
But sometime when I left the car at night and I come back in the morning to start it, it doesn't want to start. The engine crank but not start.
The weird thing is that, if I use some ether or I start in a downhill, it start immediately and it run normally.
It almost seems to have reached a certain rpm to start (and first you say, the starter motor has already been changed with a new "upgraded" version).
There no error code in the diagnostic, and as I said when the engine start the problem gone and the car is perfect.
We check the cam sensor, the temperature sensor, oil sensor, in short almost all the engine sensor and all seem to be fine.
We change the ECU with a new one copying the data from the old, we remove the immobilizer, we test the low pressure pump and we can try to change (for a week) the medium pressure pump, we clean and restore the injector but nothing work.
I'm running out of ideas and the problem is still here.
If anyone have any idea please help me, I appreciate.

(My last idea, but is something desperate, is that there is a kind of starting procedure, probably software, that the ECU use only when it start the car after a stop period, and something in this procedure goes wrong and the engine not start. But as I say, it's a teory):

Have similar problem on my 1.9 Tdi , never tried to start downhill, but some times it wont start and it turns up radiator fan full speed.
I have inspected it mechanical and i didnt find nothing. Check timing belt maybe slipped , check wiring , check instrument cluster , check ecu maybe soaked in water under wipers.

Solved for me
 

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