Alarm Going Off for Mercruiser 350 Mag MPI

[Rich990]

Boat: 2015 Regal 2100 - weighs about 4,000 pds
Bravo III
Sterndrive
350 MAG MPI

I have an odd thing happening with my boat. About once every time out, my one beep constant alarm goes off. I stop the engine and restart and the alarm doesn't go off again. I have had this happen a dozen times now. All gauges read normal when the alarm goes off (temp, oil pressure, rpms, voltage, etc.)

Most of the time, it is within the first 15 minutes of my initial engine start when this happens, and all but one time it was when I was fully underway at about 20-25 mph. Twice it was when I had a wakeboarder behind the boat (meaning usually it is just when we are heading out for the day when it happens.)

When the alarm fires, the boat decreases in speed. I usually stop the boat immediately and cut it off. Then restart, and all seems to be good. Anybody with any guesses here? Taking it to a mechanic this week, but would like to hear some thoughts that others might have on this. Here are things I have been thinking about:

* Gear lube alarm. This seems like the logical one because I see a lot of things online about this giving false positives because of a stuck float. However, the engine seems to slow when we get the alarm and I believe that doesn't happen for gear lube based on my what I have read online.

* Injector not firing. Perhaps, this is it. The rpms are normal (below 3000), but I am cruising pretty slowly (20-25 mph) when the alarm goes off. Maybe the rpms would stay low on V8 when you are cruising at that speed?

* Some sensor not working properly. Not sure which one, but this seems to be logical as well.

Anyway, any assistance would be appreciated. Thanks.

 

[Earl Cordova]

There are more sensors on your boat than you can imagine.
You need a code reader, I purchased one several years ago
and it has more than paid for itself.

 

[QBhoy]

The iac failing does similar to this.

 

[Rich990]

I had an iac fail on my last boat, and that was always issues at startup. The boat always starts fine here. Could this be IAC even though the issues usually only occur while underway?

 

[QBhoy]

I had an iac fail on my last boat, and that was always issues at startup. The boat always starts fine here. Could this be IAC even though the issues usually only occur while underway?

Mine beeped every now and then when the IAC failed. Only knew what it was when I looked at the alarms registered on the vessel view smart craft. Changed it. No beeps anymore. Think it was like 2 beeps every few minutes from memory.

 

[alldodge]

I'm with Earl, your motor needs to be scanned for codes.
I would suspect the water pressure sensor or exhaust overheat. Its not the gear lube because that one went to a 2 beep and not constant

 

[Earl Cordova]

I'm with Earl, your motor needs to be scanned for codes.
I would suspect the water pressure sensor or exhaust overheat. Its not the gear lube because that one went to a 2 beep and not constant

I just replaced my water pressure sensor for the fourth time in 16 years.

 

[c1steve]

Impeller could be weak, causing low water pressure. The Merc Guardian system is reducing your RPMs to 2,500. Best to get a code reader.

 

[OllieC]

I just recently posted a thread. I had what I thought to be an alarm, but what was happening was I was stalling out and then the ECM was going through it’s restart process by sounding a single alarm, and then the fuel pump goes on. At higher rpms it would beep, and then the rpms would lower. After spending $2k on a new ECM, turned out it was the crankshaft position sensor. It did not throw any codes. $100 at Napa. Just a thought. Mine is a 2005 5.0 mpi - should be the same crankshaft position sensor.
Wasted all Summer trying to figure it out and paid two techs, one with a scanner who saw nothing.

 

[OllieC]

Any news?

 

[Rich990]

Thanks everyone for their response. I don't think this would IAC because it only beeps once (constant alarm), but you never know. I am waiting to hear back from the mechanic. Unfortunately, anytime you take to a mechanic here (Lake Gaston, NC), it is usually at least a two week wait.

Water sensor issues make the most sense to me, but I really appreciate everyone's feedback. I wanted opinions because several times I have taken boats in and the mechanics have been unable to find the issue over the years, and at least I can ask if these things have been checked. Hoping this is a few hundred dollar issue, not thousands. Thanks again. I will let everyone know when the mechanics come back with a response.

 

[alldodge]

several times I have taken boats in and the mechanics have been unable to find the issue over the years

Sounds like there are no true mechanics in your area, just parts changers
I feel your pain and hope it can be fixed

 

[QBhoy]

To be Fair…for about $200 you can get a gadget that will tell you exactly what is going on.

 

[Fun Times]

Check your ignition power sources/wiring for loose connections starting at the key switch as it may be turning off and on the ignition randomly which is usually a one beep reset mode and if so, it wouldn’t show a code on the scanner tool…But would drop RPM.

 

[Rich990]

To be Fair…for about $200 you can get a gadget that will tell you exactly what is going on.

Hmm. My mechanic said his device cost $6000. I did see this online, but it looks like you might need to buy the software for your specific engine. https://autoplicity.com/11229985-si...eDbNRy3IAjqIWaYK1XzIq88_GR_gfPkcaAhQVEALw_wcB

 

[alldodge]

Don't know about the $200 but
Techmate Pro $599
Diacom $749
Will need adapters 94029 $249 and 94032 $59 for either the above

 

[Fun Times]

Or the lower cost way to help monitor either MPI codes / basic problem descriptions would be buying / installing certain Smart Craft gauges or Merc Mobile Vessel view ran by your iPhone, etc..,< Depending on year of MPI engine model.

 

[Rich990]

So it turns out that my impeller was in really bad shape (totally falling apart.) The mechanic replaced the entire housing because it had caused some scoring, etc and caused other damage. Because of the location of the impeller, it took him 5.5 hours. It was a small fortune. Anyway, I didn't think it could possibly really be the impeller because the temp gauge was always good. I thought it was going to be the sensor. The mechanic said that the boat was still cooling properly but I likely would have had more major problems if I waited any longer. Thanks all for everyone's help. Maybe I'll buy one of the devices in the winter after the sticker shock from this goes away... but that's a lot of cash for device and I'll likely need the mechanic to actually fix it anyway.

 

[alldodge]

Glad your fixed but 5.5 hours to replace is a bit much. Doesn't take me that long and I have to hank upside down to get

 

[Rich990]

Thanks everyone for your help on this. I'll let you know if fixing the impeller resolved the alarm issue once I have boated with it a few times.