Find a diagram of YOUR engine year and look for sensors. It has an IAT (Intake Air Temperature) sensor- check its resistance and see how that compares with the spec. That sensor is used to increase the fuel economy and if it measures outside of the normal range, it may cause problems but in this case, I would check the Fuel System sections of the manual.
I found the manual below-
www.manualslib.com
I found the manual below-
User Manuals: Pcm 5.7L MPI - EX 343 Marine Engine
Pcm 5.7L MPI - EX 343 Marine Engine Pdf User Manuals. View online or download Pcm 5.7L MPI - EX 343 Marine Engine Owner's Operation And Maintenance Manual
www.manualslib.com