Just a thought, have you declared your volume and pitch variables as floating point with '#'? (i.e. Global engvolume#=0.5)
If you haven't then the variable will be an integer and will have no effect when you alter it by fractional amounts. This will also explain why the debug shows zero values.
If you haven't then the variable will be an integer and will have no effect when you alter it by fractional amounts. This will also explain why the debug shows zero values.