Engine Alarm help

My 5.7EFI Bravo III was just fixed with a new raw water pump. I took the boat out when after idle speed for awhile I went on WOT when the engine went on half RPMs ( I think this is a safety item I can't find in the service manual book anywhere) and the alarm went off. I thought it might have been a plastic bag caught on the water intake. I shut it off and then turned it back on and returned to ramp. It ran fine so I continued on my trip at all speeds for about 2 hours. Boat ran great. Temperature gages where 150 to 175 degrees. I returned to the ramp when I decided to put it in neutral and rev up the engine. The alarm when on again. I took boat out flushed the sea water and flow was very good coming out of exhaust? What could it be? My alarm or belts to loose or what?

Check easy stuff first... is belt tight enough? Correct water pump?

bad water flow sensor? something put it in Guardian Mode. low oil pressure?

will recheck water flow system and I hope it is not low oil pressure and if it is I hope it is only the oil pressure sender switch. Will let you know what I find.

Just came back with the boat on another test run. Again, just after I ran for about 15 minutes in a no wake zone and I started to go faster the alarm when on and the boat RPM went down I guess I have a Guard Mode system. I stopped the engine and looked inside the hatch and all was good, Oil level was fine on both the engine and outdrive. The Temp gage was between 150 and 175 max and oil pressure was at 39/40psi all the time. Started the boat and ran for another 45 to 60 minutes at all speeds and no problem. Before I took the boat out of the water I changed the engine oil and filter and noticed that the oil filter was full with oil so I guess that means that the oil pump is working. Any ides what to look at next? Did the guy put in the proper temp gage ?

Just completed my 3rd. test run and all was fine until I came back to the ramp. I wanted to see what would happen if I stopped the engine and then restarted it. Well, It started fine and ran for a few minutes so I turned it off again and restarted it. this time went I started to go in gear the speed reduced RPM and the alarm went off. I am waiting for my tech to get his scanner back so we can check the codes. Any ideas would be helpful. The temp gage and oil gage were looking good during the hole day.

Sorry for the late reply. The scanner did not show any codes. We still don't know where the problem is.

Checked to see what codes in system but no codes showed up. I guess I have to start over again and try to get the scanner connected when I take the boat out in the water and see what happens.

Power limited operation is usually an indicator of the "guardian mode"....This by itself doesn't mean you have a trouble code set...what it means is the computer has detected one or more conditions considered potentially damaging to the engine. Depending upon the engine and the program in the ECU, the self-protection feature gets more complicated with technology.

If there is nothing obvious, the easiest way to resolve that class of issues is to get the scan tool and check the suite of sensors that invoke guardian mode....once the power reduction starts, it shouldn't be too hard to find the problem.

The factory service manual is the first stop to get enough insight to start the troubleshooting...

I guess I'll have to take the boat out in the water and see if I still get the alarm and engine in guardian mode. My service guy did not take the boat to the water. He just ran it in the shop and checked to see if he got any alarm so he could read the code. He did not get anything on the scanner. He however did check the wires and said he cleaned the fittings that were green and cleaned the ground wire.
I guess nee the scanner and mechanic on the boat and hope I can get the problem when the scanner is connected. 'llty running the oa I the water tomorrow and see if his cleaning the fittings did anything.

Took the boat out for a test run today. It worked fine except the alarm went on after about 15 minutes running the boat. The alarm went on for only a few seconds then went off. Did not go on reduced power. Ran the boat for another hour stopped had lunch then went back to the ramp with no problems. It must be just a week connection somewhere since it only happened 1 time today and just for a few seconds.I guess I'll have to wait until it happens more frequently

Just an update of what I have. My 1997 SeaRay 240 (OK022420) has a 5.7LXEFI Throttle Body Fuel Injection system with a Bravo lll outdrive. I'm not sure if I have a MEF1 or MEF2 or something else. New engine long block installed 2007. I was a little to late in changing the BRAVO Water pump impeller for it's annual check before the pump went out on me. I had a mechanic change the impeller pump since I can't do that stuff anymore. He also flushed the system and changed the thermostat.
After that work is when I started having the problem. I thought he might had pulled a wire or damaged a sensor somehow.
My latest run this week had the alarm go on for about 4 seconds then turn off with no engine reduced RPM this time. Keep running the rest of the day with no problem.
It's not that easy to ask a boat repair mechanic to borrow his equipment, so I'm willing to have a mechanic check the system and pay for his skills, but I want to make sure the problem happens when he is there. There is a service mechanic on the water close to where I put my boat, so I will probably use him the next time I have the problem if I can't do it myself. Since, the last trip had only the alarm go on then off in a few seconds, I'm leaning to a loose wire or bad connection somewhere. When I had the boat in the shop last week the mechanic said he cleaned some of the connections that were green and dirty.
I'm pretty sure it should be a wiring issue now so I think I will head in that direction. My first check will be the wires connected below the thermostat that he replaced.

Will do

I am really confused now.We ran the engine with all alarms disconnected and the engine still went what seams a guardian mode for a short time. Could it be a backfire?It only did it 1 time. I didn't hear and pop or bank it just lost power. We put it in idle and then it ran fine after that. Will put in new spark plugs and check wire.
If it had anything other then the 3 alarm checks would the alarm go on if there was a bad fire?

Hook up the scan tool and take it for a ride. You will see what is out of line.

Just an update. Changed the spark plugs and found some clogging in the fuel injection screen. Replaced the screens and ran it today and had no problem. The scan tool did not help with anything. I'm still confused on why the alarm went on for a few seconds when here appears to be no problem with water flow, outdrive oil or lube oil. Maybe there was no guardian mode but just a cogged up screen.Boat ran great today and will do it again on Sunday.... Ii hope.

GossDarn.Did it again took the boat out 2 times
and within 15 minutes run time the alarm went on and boat went to low RPM. Shut off engine and restarted and it ran great the rest of the day at all rpm's and speed. What do I do next???

i also have a bravo iii, I am not an expert, however I did have similar problems. my impeller went bad, all of the impeller flaps completely gone, just a stem and impeller debris all over the place, which caused water circulation issues and my backflow exhaust flaps melted also. I could run up to 10 minutes on muffs and on the water at low rpm. then an temp. alarm.

you changed you water pump and impeller and tstat and flushed your raw water system and continue to get random intermitted alarms. maybe check your temp. gauge, how long do you leave the engine running after and during the alarm? allow the engine to run during the alarm a little and see if temp gauge moves hotter. that will tell you if its water flow related. and you might not get a code.

if it were electrical or damaged mech. you would always have the problem i would think or something big is about to fail like an oil pump that would give you an alarm.

you have a water flow issue and maybe a debris has clogged and gets stuck in random positions causing the alarm. i had to undo every water hose and back flush and forward flush the hoses and water chambers. Maybe recheck that all of the new parts are good and back flush your water system with hoses disconnected maybe your flush was weak.

if the boat worked fine last year then what has changed. look there.

The system was totally check after the new impeller and tstat was put on.The alarm and reduced engine rpm whet on only 1 time after I ran for about 15 minutes. After I shut the engine off and restarted it it ran great for the test of the day. Engine temp is very good all day long.

ok, lets go with the idea that all new parts are in working condition mechanically, and oil pump is also mechanically good. next is to look at a loose or better yet a dirty corroded contacts. disconnect and connect every fitting, check battery for full charge, check all inline fuses for a good clean connection. maybe a selco book to help you find your connections.

what is the depth of water you are running in when you get the alarm? is there a lot of vegetation in the water or muk and slit?

The connections were the first things check by a certified mercruiser mechanic.After that I put in 2 new batteries (cranking and aux) I use both batteries in the on position all day long.
I got to get it to do this problem more often so we can zero in on where the problem is coming from. It's just funny that it started after the water pump and tstat were replaced.
The water flow system was completely flushed out and all the impeller stuff was found.

What is the serial number on the engine and what year is it?

engine #OK022420 1997 5.7 EFI Bravo lll outdrive
Do I really have guardian mode or not on my engine?

Almost had a grest day. Boat ran great. No alarm or reduced power. Whatever is the problem I didn't have it this week. The only problem I had was towing the boat back home a bearing went out on me and I will have it fixed next week, Good thing I have a duel axil trailer and I was able to get it home.