Merc 5.0 NO start

[WellcraftSportsman23]

Ok guys here we go. I have a Merc 5.0 EFI that is giving me a hard time.
Everything was running fine last weekend. Last night we got a huge rain storm and I went to the boat to make sure all was well and tried to start the boat. Usually she starts in 3-4 seconds with out fail. Today it took a bit but it did start. I decided to turn off because I heard a squeaky belt. I tightened the belt and tried to start and NOTHING. It was turning over but nothing, no start. I took off fuel water separator and drained and all was ok, I took off flame arrester and watched as the EFI shot fuel into the carb while turning over. Messed with the Coil wire and it broke. Finally got new wire and tried to turn over and still nothing. I got frustrated and gave it full throttle while starting and it turned over but did not run well. Got it to idle but was not sounding good. Turned off and would not start again. What can I do?

 

[Fun Times]

Hi there, since it rained, you may want to try pulling the distributor cap and see if any water/moisture has worked it's way inside.....If that's ok then you'll want to check for consistent spark both out of the coil wire and at the plug wires. The use of a timing light helps make this job easier.

Then you'll need to see how much fuel pressure you actually have...Be sure that battery is in good healthy condition with around 12.6ish volts and around 750+ cold cranking amps to go with it.

Also be sure no water from above the engine can leak down past something such as a bolt, hole, vent, etc. to allow water to fall in/onto the distributor assembly or Throttle body components or wiring connections.

 

[alldodge]

I got frustrated and gave it full throttle while starting and it turned over but did not run well. Got it to idle but was not sounding good.

:welcome: to iboats

As it could need to dry out some more, it could also be coincidence but the IAC may be the issue. If you can get it to start by giving it some throttle (not wide open just some) and it dies or idles rough when brought back to center.