4.3 MPI Diagnostic Readings for no start

I have a 2007 Mercruiser 4.3 MPI Alpha drive that all not start. It cranks but no start. End of last season it ran great. Pulled it out of the water, it sat for a week then went to winterize it. I started , ran really rough for a few seconds, backfired and died. Could not get it to start after that. Took it to a local boat mechanic, he could not Get it started either and advised that we take it to get scanned. He winterized it for us and we put it in storage. Pulled it out of storage and now trying to figure it out. I have access to CDI MEDS software for a day or two. Was wondering what readings I should focus on. Fuel pump primes to 43 psi but bounces between 38-43 while its running then drops to 38 when pump shuts off. Spark looked weak at the plugs so replaced coil, module, dist cap and rotor button. Posts in dist cap were coated with a tan looking corrosion.The CDI software was ran with key in on position. Had the following readings:

ENGINE RPM: 0 RPM
ENGINE LOAD : 59.3%
TPI 1 VOLTS: 0.56 VOLTS
AIR TEMP: 80.6 F
MAP PRESSURE: 14.18 PSI
FUEL LEVEL: 1015
PITOT: 0
SHIFT : 4(NEUTRAL)
OIL PRESSURE: 0.41 PSI
TRIM: 254
BATTERY VOLTS: 11.87 VOLTS
PWR 1 VOLTS: 4.96 VOLTS
TPS% : 0.1%
SPARK ANG BTDC: 8.0
AVAILABLE PWR%100.0%
LAKE/SEA TEMP: -31.0 F
PADDLE WHEEL: 0.00
BARO PRESSURE : 14.19 PSI
SEA PUMP PRESS:0.00
IAC PWM% :0.0%
ECT : 75.2 F

Fuel pump was replaced last year. Fu8el pump relay test on the CDI software passes and I can hear it clicking on and off. The main power relay I can not hear click and it fails the test. But the relay is good when I bench test it. Any thoughts on what the issue could be or what readings seem off would be greatly appreciated. Thank you

If the scanner is talking to the ECU, the main relay is engaged...

the only things in your list that I see is the battery is low...may need cables cleaned or a good charge.

if you have fuel in the injector rail and spark, it should fire...test for spark using a good spark tester...a hot spark is normally blue and will jump at least 1/4"...noid lights are good for testing the injector pulses...

spray some starting fluid into the throttle body, if it kicks, then you know its fuel related,. could be an ecu issue, did the scanner show any fault codes?