I think I know the answer.
 

502 MPI. If the vacume hose comes off the fuel pressure regulator will it cause it to run rich. I was smelling a very rich condition and hart to restart. Acted like it was flooded which I think is what was happening. I think I knocked the hose off when I took the thermostat out for winterizing. Havent had it back out yet to see if putting hose back corrected problem.

Jerry.

true enough but not enough to do what you say... if i remember correctly w/o the manual in front of me there is only a 3 or 4 psi dif ... from 43 to 39 . i was chasing a problem one day and ran the motor with it both ways extensively with gages on it and it made effectly no difference at all... fix it by all means but if its rich at idle i figure its something else.... suggest you firt make sure the water and air temp sensors are plugged in and working properly. this is where the scanner will save your ass.

As far as I know the the vacuumhose will transfer the intake manifold vacuum to the fuel pressure regulator ie up to 15 psi at idle and at acceleration basically nothing.

Stevesxm: Thanks for the reply. I read about a shorted injector that gave you fits so you have had a learning experience with this system. I thought I might have a bad diaphram in my VST causing the problem but when I found the hose of I figured that was it. Althou the hose is a bit soft so I wonder if the regulator may be leaking some. Or the hose may be just getting old. I got a new piece of hose for it and will check for fuel in the hose next time out. I may take a hand vacume pump along and see if it holds vacume. Is the regulator hard to replace. Have not had one off the boat engine. Many times on cars. I may have to invest in a scan tool at some point also. Puts things to rest much easier.

Jerry.