Originally Posted by GAS GUY
I have a good vacuum signal going in from the engine but the inlet pickup side of the pump had nothing so the diaphram in the pump body is not working.
You are correct that it could be the diaphragm. But it could be a flapper valve.
If either valve is not working -- either not sealing or not opening -- the pump would show the symptom you describe: no vacuum on the inlet side. The pump could be simply "breathing" through one side or it could be stuck and acting as an air shock absorber.
Please excuse a post full of speculation.