Fuel pump or PCM?

I have a '92 f-150 inline 6 EFI with 221,000 miles. It is on it's 3rd fuel pump now and worried it may need a 4th. Here is the problem: if i turn the key on and the fuel pump primes normally (5 sec.), it will start fine. If the fuel pump runs non-stop when the key is turned on, it will not fire up and the engine just spins over. I have pulled the PCM and checked for corrosion, replaced the ignition module, coil, and MAP sensor. Any ideas would be helpful.:banghead: