not pumping?

I have a Chem-Tech 100 30gpd chlorine metering pump. The injector was blocked with scale so it was cleaned and replaced. Could not get the pump to prime. So, replaced both the discharge and the suction valve seats and balls, new injector and pump diaphragm. The pump will prime at the valve and will also pump when the injector is removed from the pipe with no pressure. Once in the pipe and well pressure turned on it stops pumping. The pump still runs, but no fluid movement that I can see in the tubes and water smells like eggs still. Do I need a new metering pump? Help!