Starts cold no problem, but after engine warms up and I go into a store for 10 or 15 minutes, when I come out it won't start again. When its working properly I can hear the fuel pump relay click and the pump prime for a couple seconds before I start it, but after the engine is warmed up the relay won't prime and the car won't start. If I am patient and sit in the car for another 20 minutes or so, the pump finally primes and it starts again.

I've checked and cleaned contacts on the relay and fuse as well as the fuse holder. I checked and cleaned the secondary fuel pump and filter. I checked the fuel pressure regulator - no gas in vacuum hose. What could be causing this problem? Also, there's no vacuum sound when I remove the fuel cap... shouldn't there be?

A friend told me he had the same problem and he just installed a switch on the dashboard between the fuse to the pump in order to manually activate it, but I'd rather solve the problem than create a work-around. Any help here would be greatly appreciated