I have a 1990 3.1L MPI and for some reason it is loosing fuel pressure I can test it and it hits 45 but drops to 0 as soon as the pump shuts off.

you have one of a few things going on. could be a stuck open injector, a bad regulator or even the check valve in your fuel sending unit....

Probably the check valve in the sending unit. I have worked on alot of those 3.1's. i hate em!!! My advice is fix it the sell it.

Probably the check valve in the sending unit. I have worked on alot of those 3.1's. i hate em!!! My advice is fix it then sell it.

No kidding on that engine being a piece of crap, whoever heard of a hollow camshaft? So as a result, they have a tendency to break in half or threes