2002 Mercruiser 350 Mag MPI showing high temp and engaging guardian system

[AGraham]

Hi, we have a 2002 Ski Centurion with the 2002 Mercruiser 350 Mag MPI engine. We have been having a heck of a time with it and need some help. We had troubles with it cutting out at waterski speed and shutting off then engaging the guardian system. So over the winter my husband changed out several things and it ran great with no issues for several times out this season. Then this week it started doing it again and we had it scanned by a repair guy and the code was that it was getting too hot but with all inspections it didn't really seem to be too hot. We have replaced several things over the past week; thermostat, distributor cap, throttle position sensor and the iac valve. You can run it to do wakesurfing if you accelerate slowly without it beeping however if you accelerate too fast or go faster than about 12-15 it shuts down and beeps. The only other thing we can thing to change is the water pressure sensor and my husband is going to take another look at the impeller. We are really frustrated and not sure what to do next any suggestions are most appreciated!!! Thank You!!

 

[Scott Danforth]

Did you service the raw water pump?

 

[AGraham]

Did you service the raw water pump?

My husband is going to pull the impeller and check it. Is that what you meant?

 

[Searay205]

What kind of outdrive or is it inboard. Don't forget to look at what could be blocking or impeding flow TOO the pump on the suction side. Kinked hose, air leak, etc.

 

[AGraham]

It is an inboard. My husband has pulled every hose and changed out the impeller, pulled the other water pump and checked and cleaned it. He has also put in a new IAC as well as a new thermometer, throttle position sensor, both temp sensors, oil pressure sender and distributor cap. The only other thing we can think of is the water pressure sensor. Anything else anyone can think of that would be causing it to overheat?

 

[Fun Times]

It is an inboard. My husband has pulled every hose and changed out the impeller, pulled the other water pump and checked and cleaned it. He has also put in a new IAC as well as a new thermometer, throttle position sensor, both temp sensors, oil pressure sender and distributor cap. The only other thing we can think of is the water pressure sensor. Anything else anyone can think of that would be causing it to overheat?

Have you been able to verify the engine is actually overheating still especially when the beeping is happening? What does the Temp gauge read?... Search online "infrared temp gun" which this tool would also help tell you what the engine temperatures are too.

Bear in mind that there's also a chance the scan tool may have told you the engine once got hot but then the situation may have corrected itself someway and the technician read you a passed fault code from the scanner to where you're not dealing with an actual or false overheat situation at the moment... Typically with the ECM type i believe you have you'd erase faults and see if it comes back.

With that mentioned i "believe" your engine model has a fuel pressure sensor but to know this for sure we'll need the engine serial number.
If you have this fuel sensor then you may have to low of fuel pressure which you'll need to connect a fuel pressure gauge up the fuel rail schrader valve (think tire air valve) and see what the fuel pressure is under way / engine load as this sensor would sound the warning horn too if it's on your engine model.

 

[AGraham]

Have you been able to verify the engine is actually overheating still especially when the beeping is happening? What does the Temp gauge read?... Search online "infrared temp gun" which this tool would also help tell you what the engine temperatures are too.

Bear in mind that there's also a chance the scan tool may have told you the engine once got hot but then the situation may have corrected itself someway and the technician read you a passed fault code from the scanner to where you're not dealing with an actual or false overheat situation at the moment... Typically with the ECM type i believe you have you'd erase faults and see if it comes back.

With that mentioned i "believe" your engine model has a fuel pressure sensor but to know this for sure we'll need the engine serial number.
If you have this fuel sensor then you may have to low of fuel pressure which you'll need to connect a fuel pressure gauge up the fuel rail schrader valve (think tire air valve) and see what the fuel pressure is under way / engine load as this sensor would sound the warning horn too if it's on your engine model.

Thank you for the detailed reply. You may be correct that the overheating codes were old codes. The last time I had the engine scanned (400 hours and 5 seasons ago) I vaguely recall there only being 2 legacy overheat codes stored on the ECM. This is also reinforced by the fact that the dash guage was reading hot between 200-220 while the computer diagnostic was consistently reading 154 in real time during a "fake lake" test at various RPMs (incidentally the Guardian alarm never went off during the fake lake test). I only continued to research the "overheat" scenario because the mechanic and I both felt like the exhaust manifolds and water supply hoses that go to the top of the thermostat housing felt hotter to the touch than they should. Clearly that is subjective and non-conclusive. Your suggestion that fuel pressure could be an issue also has me thinking. With only a couple of exceptions, the Guardian alarm has been triggered when accelerating from "just in gear" to full throttle to pull a slalom skier up out of the water, during a waterski run with sustained speed above 30 mph or more recently when accelerating gradually above 15mph. When the Guardian alarm sounds in the first scenario (waterski start) or the third (gradual acceleration thru 15 mph) there has been a momentary hesitation/roughness that passes thru. In the earlier stages of the issue, the boat would continue to run with the Guardian alarm sounding (even continuing to pull a skier at 32-34 mph (assume this is because Guardian only applied limited restriction to power output). More recently, as the issue has become more constant, the boat will completely shut down as the Guardian alarm triggers). Would a fuel pressure sensor error that triggers the Guardian not produce a code that would be detected/stored by the ECM? Granted, the mechanic and I were both focused more on temperature related data points during the "fake lake" test, but we watched it for quite awhile (at least 20 minutes of run time) and there were no unusual readings. The S/N for our engine is 0M311184 (Mercruiser 350 MAG MPI Ski (2002))

 

[Fun Times]

Thanks for the serial number as it helps find the right engine model you're working with especially since 2002 was right near a big transition year of engine model change. With the help of the serial number, it shows your engine does not have the fuel pressure sensor i believed your engine to have had so please disregard my first thoughts of theory of a low fuel pressure sensor sounding the warning while reading your symptoms as that can't happen with your engine...The model design before yours had the fuel sensor i was thinking of.

I'll suggest considering with the amount of $$$ you're spending on parts that hope to work, it might be time to consider either buying or renting a marine type scan tool.

I just found someone renting the software to plug into a laptop on Ebay for $70.00 but $400.00 deposit you get back for 7 day rental..., https://www.ebay.com/itm/284931466798?hash=item42573d262e:g:2VEAAOSwJNdi-B6m&amdata=enc:AQAHAAAAoBybZjE8lf86SYL6BhLZpBsdQ77PayFAE6YTvUaddDrnuWUyTf0FUJf7MlhK893YrtL6aTiLlBQiIfntsGZYKtYpQ2IPD8ycihQvdYjkfhuo7dDuAPjvr/qkKQowkLQHXWqfjzC4QdKeKwDQgf0/HM3REhVO9Zt+4+UJWoy20Ot9bjqMc1PFDlV+xkNSrqHyE8I6HvbJ+lK5yzjb0j6lad8=|tkp:Bk9SR4CW6NXUYA

Or depending on budget allowed, consider buying direct from Rind technologies in Chicago..., 773-736-6633
Here should be the list that would work on your engine system,

MerCruiser3 – Rinda Technologies Inc.

The techmate Pro is a popular one to have, https://www.rinda.com/rindashop/shop/techmate-pro/techmate-pro-94706

Either way you'd need this adaptor to read your ECM if desired to consider this route, https://www.rinda.com/rindashop/shop/adapter/94006

Here is your engine parts that fit your serial number for you if needed, https://www.mercruiserparts.com/350-mag-mpi-ski-0m317000-thru-0w689999

I doubt this would be your issue you're having but your engine falls within some of it via serial number and engine model so i'll leave this bulletin here for you to at least know about it's existence..., https://manualzz.com/doc/23430314/service-bulletin---marinemechanic.com

Also make sure you are not losing any 12 volt power anywhere under power as that could sound the warning horn too and cause a hesitation type symptom. Gently wiggle wires including the wires at the back side of the key switch.

Hope this helps some, good luck.

 

[AGraham]

Thank you for all of the great info, I really appreciate it. We are continuing to troubleshoot, and are going to try one more part, a water pressure sensor to see if that makes a difference. Given that we have had it scanned already and gotten the overheat codes I think the next thing we may do is have someone come down and look at it while it is in the water as it does not recreate the problem on the fake lake. Hopefully we can get to the bottom of this soon!

 

[nola mike]

Is it not possible to wipe all codes from these ECMs, or are legacy codes forever available to see?