Effects

I have been experimenting with effects and for some reason some type of effects work fine and some don't show up at all.I know there is supposed to be smoke coming out of the factories, but not on my machine, no matter what settings I try. But the engine start smoke, smoke trail, etc. work fine.I compiled a few bgls with effects. fx_steam1.fx for example works fine but fx_SmokeStack.fx or fx_SmokeStack2.fx does nothing.Does anyone have any experience what causes effects not to show up at all ?Thanks,Matthias