FAC and FAD

I have an old rifle that i dont use it any more and i disassemble it regrease it and add some oil in the compresion chamber. I heard that adding more than it should in the pump chamber can cause a detonation FAD(fuel air detonation) instead of FAC(fuel air combustion). The rifle uses a leather pump head and absorves most of the oil. When i shoot i see hell a lot more smoke than i used to see when using it long ago. Are there any specific things i should be aware of so there would not be any acidental detonation in the chamber? Is this "detonation" in air rifles realy dangerous?