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NEED HELP ASAP. Merc 350 issue

M

mcg121

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I have a Mercury 350 MPI Horizon. 2 days ago it ran for about 10 minutes then shut off and wouldnt start. Sat out in the water for over an hour and it restarted. Noticed it was making a strange sucking sound above 2500 RPMs but made it slowly back to the marina. Thought it was a fuel filter issue but replaced them. Now it starts in neutral for about 5-10 seconds but jumps between 200 and 600 RPMs before shutting off. If i give it any throttle it will shut off immediately. Could this mean the fuel pumps are going out? or might it mean an issue with one of the sensors?

I am on vacation and would like to get this fixed very soon, so any help is greatly appreciated. Thanks.
 
Welcome aboard ! Pull all the plugs and crank the engine... see water shooting out the plug holes ? Maybe just the back ones ? Do a compression test with all the plugs out, throttle fully down on a warm engine. Get back to us !
 
After replacing the filters today, we started it with some throttle and it ran fine for a couple minutes. Then the rpms dropped. After that it only starts in neutral for a few seconds. Yesterday it ran great in neutral for about 15 minutes even with throttle, but when we tried to take it out, it only ran in gear for a few minutes before shutting off. Then just like 2 days ago it had to sit for awhile before we could sart it again. Seems to be getting worse.
 
Check the throttle body base nuts for tightness. Unplug/reconnect each injector...look at it for corrosion at the plug.
 
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