My fuel pressure is reading about 16. The other engine is 37. When I turn the key I can still hear the fuel system priming itself. What may be the problem??? Mechanical or electrical pump??? I would appreciate any help...

Has anyone had this problem occur with a mercury 525 efi and what was the cause?

Not sure about 525's, but the 496 has two pumps. One is a boost pump located near the separator. It supplements the main pump on the lower port side of motor. Noraml PSI at the rail is 38-43 psi. A bad boost will drop it into the sub-20 psi range. Been there done that.

If it were a 496 I'd say the boost has/is crapped out?

I changed the filter and shortly there after noticed the problem. I will look at the possibilty with that pump. I appreciate your opinion...

You may have a bad fuel pressure regulator, I had this happen on my 502 MPI, dropped one to 18 psi at best. If a boost pump is weak you should still have good pressure with key on or at idle.