Hello all
have a 502 mpi that I have trouble starting boat when cold - motor runs fine when warmed up just has a hard time getting started.
I checked the fuel pressure from the Schroeder valve, place the key to on mode pressure goes up to about 30 (that’s when fuel pump cuts off) pressure immediately drops back to 0.
I have since started the engine with regulator on and pressure is at 52 psi. I take vacuum line off from fuel pressure regulator and pressure goes up 5-7psi, insert back and pressure falls to 52-53 psi again.

need help is the fuel pump bad or leak in injectors?

You have a leak. Pressure should not bleed off like that.
pressure should be around 35-43 depending on application. Post your serial number and some one will have the spec fo you.

Wot during crank makes ecu go into ‘clear flood mode’ ie: cuts fuel.

So, yeh,?as mentioned could be keak. See if there is fuel going from mechanical pumps yellow vent line into intake. Same from your vst electric pump housing.

If all clear and no signs of raw fuel getting into intake, time to check fuel psi and some sensor readings.

After you fix the fuel pressure issues, then do a leak down and compression test on the motors.

Okay, guess I’m guilty of not carefully reading the OP. Sorry.

VST systems ran at about 36psi and Cool Fuel systems 43psi.

Agree with others on where to check fuel psi dropping fast. If you get to the point of checking Injectors and going to send them out, member ArcticFriends foes this, amongst many things, snd you’d be hard pressed to find someone more hands on knowledgeable with these 502MPI,s. And there’s lots if kniwkedge on these motors here on OSO. At one time, these where in most people’s boats here.