Nissan CD20 is 3 cylinders

As they are, I raise the case to see if anyone can give me some idea, the engine is Nissan Sentra CD20, with hydraulic dumps, started starting failing in 3 cylinders, loosening the pipe of the injector 4, and purge it on and accommodated and for the whole day it did not fail anymore, I took the firefighter I checked the injectors and pump and they are well Poquito I stayed more serene but we started and started in 3 cylinders and no matter how much we loosen the injector 4 -cylinder injector pipe, they told me that it can be a hydraulic baded that has no strength so it does not open the valves of the 4 and therefore it does not compress, can it be? How can you try a hydraulic botner outside? Any other idea?

You just talk about taes I also imagine if they were a lot and so that one will observe the oil the dirt could be