Boat was running good came off plane and port motor did not want to run right started running rough. Then the beeping started 5 beeps 3 seconds long. Looked in my Mercury book and it said. Coil pack failure,Fuel Injector failure,Fuel pump failure,Idle air control failure. Got the boat home plugged it into scan tool coil failure number 2. Replaced coil still ran bad changed mechanical fuel pump,replaced IAC, replaced Map sensor, checked fuel injectors, replaced fuel filters and replaced spark plugs. Took PCM off bad motor put it on good motor it ran great. The only fault code I get is 17 Map Sensor Idle Fault. Looking at the scan tool while running it seems to think it is under boost at Idle. IAC is at 44.6% and Spark advances is at 19.0 degrees Manifold pressure 14.6 psi and fuel pressure is 67 to 70 psi. Good motor at Idle, IAC 0.0 % spark advance is 0.0 manifold pressure 10.1 psi and fuel pressure is 59 to 61. I am thinking maybe a sensor is bad, not sure any help would be greatly appreciated. There is nobody local that works on these motor so trying to figure it out on my own.

Thanks Jack

Not really familiar with that eng but does the MAP sensor have a vacuum hose? If so, I'd check that. May be cracked.

Just an idea as I have no knowledge for 700's does it have spark at #2, check with putting coil wire on spare plug grounded?
compression check
can the scanner read live data from sensors
I have rinda PC version which can record data

It does not have a vacuum line attached to it. It is electric.

All the coils are good check them all have spark. Compression is good. All it tells me is I have 5 volts to sensors.

certainly sounds like a sensor issue, or wiring to the sensor connector, you've ruled out the pcm

Yes I took the Pcm of the bad motor and installed it on my good motor and it runs great. I was thinking sensor also or boost control valve.

Map sensor reads atmospheric pressure key on engine off. So 14.6 psi is correct. 0 is gauge pressure

Barometric Pressure was 14.8 and the manifold pressure at idle was 14.6 my mechanical boost gauge is bouncing all over the place at idle.

is the engine surging ? like a poorly tuned carbed roots blower.......