In a single (no feather) you move the pitch control to full coarse in order to reduce drag and give you the best glide distance.
It used to be a demonstration as part of the Constant Speed Unit endorsement (it's a separate endorsement in Australia) to set up a glide, and then pull the pitch control back to point out the surge of extra speed.
Lack of fuel flow, assuming a flow gauge is fitted, would be the major indictaor.
Only if the engine has failed because you have run out of fuel.
