Failure in Pernkins 4

Hello everyone I have a Perkins 4 mounted on a Ford F 100 truck and bought it thinking that I had a bad valve for a fault that towards the regular, then it takes it to the firefighter and told me that it was an nozzle by caution the 4 and no improvement was changed, the point of the pump was modified and the same was also changed all the filters. The preheating spark plug that is not losing and nothing, valve light and correct. I already visit two bombers and several mechanics and no concrete response, I am a mechanic to be that something can happen to me by that my consultation to other colleagues, now the only thing I have left is to take out the lid and control valves but all agree that it is an unnecessary work, but I think it is the only thing that I have left, it should be noted that the fault is almost impe I appeal to you to see if you can throw an idea to me. Thank you