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Engine issues 377 Mag

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Last June went from Ft. Lauderdale to Bimini in 3-5 foot seas.  About halfway over I got an extremely loud constant beep from my Smartcraft display, with a message

showing " limited power".  Stopped and shut engine down, restarted, had no further problems for a few days.  Occurred again, mechanic said it was a bad sensor, and nothing $350

would not correct.  Same thing is happening again, and it will be a few weeks till they can hook it up on the tester.....  Anything I can do but wait.  Only happens over 3,000 RPMs.

All fluids are good... 2013 264 Sunesta 377 Mag Bravo 3.  I had one suggestion of batteries...Would old batteries effect...... 2013 batteries, but still work fine

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Wow. I would not be making that trek to Bimini in 3-5’ seas in a sunesta. 

We would need to know what the fault code is to help. A constant beep is gonna be an overheat or exhaust temp to high or possibly low voltage or one of the major fault codes. 

Low voltage can cause issues with sensors. Have the batteries load tested. Have the alternator bench tested as well. 

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It can be a alternator with worn out slip ring brushes.  They show a problem by not pressing hard enough. That causes some light BUT continuous blackening of the slip rings.  

It can be a very slow, going bad, with enough current at higher rpms. Had 2 alternators with that condition. Some brushes are just too soft.

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Over 3000 rpm, that is the clue.

Low water pressureor flow causing elevated exhaust temperatures gets my vote.

Worn impeller/water pump scoring or the dreaded bravoitis. I vote the latter.

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18 hours ago, RRRR said:

Last June went from Ft. Lauderdale to Bimini in 3-5 foot seas.  About halfway over I got an extremely loud constant beep from my Smartcraft display, with a message showing " limited power".  Stopped and shut engine down, restarted, had no further problems for a few days.  Occurred again, mechanic said it was a bad sensor, and nothing $350 would not correct.  Same thing is happening again, and it will be a few weeks till they can hook it up on the tester.....  Anything I can do but wait.  Only happens over 3,000 RPMs.

All fluids are good... 2013 264 Sunesta 377 Mag Bravo 3.  I had one suggestion of batteries...Would old batteries effect...... 2013 batteries, but still work fine

Unfortunate that the digital SmartCraft gauges in your boat won't provide block water psi numbers; sadly that function was never turned 'on' from VeeThree. Of all the engine sensor info I'd want want to look at, that would be the one along with temperature...

Sensor the mechanic is talking about is most likely the water pressure sensor located on the power steering cooler directly behind the distributor cap. Think it takes a 1" deep socket to re & re. Let us assume for a moment you're actually getting proper water block pressure. This sensor could be giving a low psi reading to the ECM causing the 'hard' alarm to come even though the engine may not be overheating. Mercury part # 8M6000623 and this job you could do yourself if you wanted to take a chance on the part. That cooler is made of brass, so don't over tighten the new sensor.

Older water pressure sensors had a white body and water would get into the circuitry resulting in incorrect info going to ECM. I haven't run across many problems with later black body style sensors in fresh water at least. Your engine almost certainly has the black version.

Worn seawater pump and/or impeller is also quite likely. What are the engine temperatures when this problem occurs?

Lastly, low voltage could be the problem, but ECM should have the horn emit a 'soft' alarm with beep...beep as a kind of early warning before going into a hard constant alarm. While under way, you should see roughly 13.8 - 14.2 for voltage on digital LCD read out on tachometer.

 

Image result for 8M6000623

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Thanks Shepherd, looking into those things tomorrow.....................will post results

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Engine has 185 hours, impeller changed at 150 hours.  

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It was 3-5 in his dreams!

Going back I could not say as my boat got stuck in Bimini.

But maybe it was 3ft tops on the way over

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4 hours ago, RRRR said:

Engine has 185 hours, impeller changed at 150 hours.  

The number of hours on an impeller is not the only indicator . If the boat sat for a long period of time the impeller can take a set and will not move as much water as it should. 

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17 hours ago, Phillbo said:

The number of hours on an impeller is not the only indicator . If the boat sat for a long period of time the impeller can take a set and will not move as much water as it should. 

So true. Also, you can pick up some sand or worst case a trash bag and trash a brand new impeller in seconds. I added a simple pressure gauge at the power steering cooler water circuit just next to the OEM pressure sender so I can monitor impeller health at a glance.

http://s526.photobucket.com/user/wingnutmfs/media/BoatDump/bilge pump_zpspy2lem7r.jpg.html

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