I'm not sure about the Pathy, but I dealt with a Chevy HHR that had an adequately working pump (running 45psi at idle instead of 50-60psi) but the fuel pressure regulator (thats built into the pump) was faulty and would let the pressure drop the second the pump turns off.
So, you turn the key on and the pump primes. Shortly there after, until you start the vehicle, the pressure goes to zero. Try to start, no fuel pressure, car wont start. If you timed it perfectly/quickly, you could link a prime and a start together and get it to limp alive.
The bad deal with the chevy was that *Everything* was built into the pump. FPReg, filter, sending unit, etc. Thing cost almost 300 bucks. But...made solving the problem really easy because everything that could have caused the condition was replaced in one unit.
I'm not saying this is your problem or solution, but its my recent experience.